feature: Added Domain Model pattern (#1795)

* domain-model pattern

* fixed optional get before check isPresent

* readme minor changes

* change currency representation with joda money

* changed names of test methods

* fixed code smells

* Update domain-model/README.md
Co-authored-by: NIlkka Seppälä <iluwatar@users.noreply.github.com>

* Update domain-model/README.md
Co-authored-by: NIlkka Seppälä <iluwatar@users.noreply.github.com>

* updated readme and diagrams
Co-authored-by: NIlkka Seppälä <iluwatar@users.noreply.github.com>

domain-model/README.md

+---
+layout: pattern
+title: Domain Model
+folder: domain-model
+permalink: /patterns/domain-model/
+categories: Architectural
+tags:
+ - Domain
+---
+## Intent
+Domain model pattern provides an object-oriented way of dealing with complicated logic. Instead of having one procedure that handles all business logic for a user action there are multiple objects and each of them handles a slice of domain logic that is relevant to it.
+## Explanation
+
+Real world example
+
+> Let's assume that we need to build an e-commerce web application. While analyzing requirements you will notice that there are few nouns you talk about repeatedly. It’s your Customer, and a Product the customer looks for. These two are your domain-specific classes and each of that classes will include some business logic specific to its domain.
+
+In plain words
+
+> The Domain Model is an object model of the domain that incorporates both behavior and data.
+
+Programmatic Example
+
+In the example of the e-commerce app, we need to deal with the domain logic of customers who want to buy products and return them if they want. We can use the domain model pattern and create classes `Customer` and `Product` where every single instance of that class incorporates both behavior and data and represents only one record in the underlying table.
+
+Here is the `Product` domain class with fields `name`, `price`, `expirationDate` which is specific for each product, `productDao` for working with DB, `save` method for saving product and `getSalePrice` method which return price for this product with discount.
+
+```java
+@Slf4j
+@Getter
+@Setter
+@Builder
+@AllArgsConstructor
+public class Product {
+
+    private static final int DAYS_UNTIL_EXPIRATION_WHEN_DISCOUNT_ACTIVE = 4;
+    private static final double DISCOUNT_RATE = 0.2;
+
+    @NonNull private final ProductDao productDao;
+    @NonNull private String name;
+    @NonNull private Money price;
+    @NonNull private LocalDate expirationDate;
+
+    /**
+     * Save product or update if product already exist.
+     */
+    public void save() {
+        try {
+            Optional<Product> product = productDao.findByName(name);
+            if (product.isPresent()) {
+                productDao.update(this);
+            } else {
+                productDao.save(this);
+            }
+        } catch (SQLException ex) {
+            LOGGER.error(ex.getMessage());
+        }
+    }
+
+    /**
+     * Calculate sale price of product with discount.
+     */
+    public Money getSalePrice() {
+        return price.minus(calculateDiscount());
+    }
+
+    private Money calculateDiscount() {
+        if (ChronoUnit.DAYS.between(LocalDate.now(), expirationDate)
+                < DAYS_UNTIL_EXPIRATION_WHEN_DISCOUNT_ACTIVE) {
+
+            return price.multipliedBy(DISCOUNT_RATE, RoundingMode.DOWN);
+        }
+
+        return Money.zero(USD);
+    }
+}
+```
+
+Here is the `Customer` domain class with fields `name`, `money` which is specific for each customer, `customerDao` for working with DB, `save` for saving customer, `buyProduct` which add a product to purchases and withdraw money, `returnProduct` which remove product from purchases and return money, `showPurchases` and `showBalance` methods for printing customer's purchases and money balance.
+
+```java
+@Slf4j
+@Getter
+@Setter
+@Builder
+public class Customer {
+
+    @NonNull private final CustomerDao customerDao;
+    @Builder.Default private List<Product> purchases = new ArrayList<>();
+    @NonNull private String name;
+    @NonNull private Money money;
+
+    /**
+     * Save customer or update if customer already exist.
+     */
+    public void save() {
+        try {
+            Optional<Customer> customer = customerDao.findByName(name);
+            if (customer.isPresent()) {
+                customerDao.update(this);
+            } else {
+                customerDao.save(this);
+            }
+        } catch (SQLException ex) {
+            LOGGER.error(ex.getMessage());
+        }
+    }
+
+    /**
+     * Add product to purchases, save to db and withdraw money.
+     *
+     * @param product to buy.
+     */
+    public void buyProduct(Product product) {
+        LOGGER.info(
+                String.format(
+                        "%s want to buy %s($%.2f)...",
+                        name, product.getName(), product.getSalePrice().getAmount()));
+        try {
+            withdraw(product.getSalePrice());
+        } catch (IllegalArgumentException ex) {
+            LOGGER.error(ex.getMessage());
+            return;
+        }
+        try {
+            customerDao.addProduct(product, this);
+            purchases.add(product);
+            LOGGER.info(String.format("%s bought %s!", name, product.getName()));
+        } catch (SQLException exception) {
+            receiveMoney(product.getSalePrice());
+            LOGGER.error(exception.getMessage());
+        }
+    }
+
+    /**
+     * Remove product from purchases, delete from db and return money.
+     *
+     * @param product to return.
+     */
+    public void returnProduct(Product product) {
+        LOGGER.info(
+                String.format(
+                        "%s want to return %s($%.2f)...",
+                        name, product.getName(), product.getSalePrice().getAmount()));
+        if (purchases.contains(product)) {
+            try {
+                customerDao.deleteProduct(product, this);
+                purchases.remove(product);
+                receiveMoney(product.getSalePrice());
+                LOGGER.info(String.format("%s returned %s!", name, product.getName()));
+            } catch (SQLException ex) {
+                LOGGER.error(ex.getMessage());
+            }
+        } else {
+            LOGGER.error(String.format("%s didn't buy %s...", name, product.getName()));
+        }
+    }
+
+    /**
+     * Print customer's purchases.
+     */
+    public void showPurchases() {
+        Optional<String> purchasesToShow =
+                purchases.stream()
+                        .map(p -> p.getName() + " - $" + p.getSalePrice().getAmount())
+                        .reduce((p1, p2) -> p1 + ", " + p2);
+
+        if (purchasesToShow.isPresent()) {
+            LOGGER.info(name + " bought: " + purchasesToShow.get());
+        } else {
+            LOGGER.info(name + " didn't bought anything");
+        }
+    }
+
+    /**
+     * Print customer's money balance.
+     */
+    public void showBalance() {
+        LOGGER.info(name + " balance: " + money);
+    }
+
+    private void withdraw(Money amount) throws IllegalArgumentException {
+        if (money.compareTo(amount) < 0) {
+            throw new IllegalArgumentException("Not enough money!");
+        }
+        money = money.minus(amount);
+    }
+
+    private void receiveMoney(Money amount) {
+        money = money.plus(amount);
+    }
+}
+```
+
+In the class `App`, we create a new instance of class Customer which represents customer Tom and handle data and actions of that customer and creating three products that Tom wants to buy.
+
+
+```java
+// Create data source and create the customers, products and purchases tables
+final var dataSource = createDataSource();
+deleteSchema(dataSource);
+createSchema(dataSource);
+
+// create customer
+var customerDao = new CustomerDaoImpl(dataSource);
+
+var tom =
+    Customer.builder()
+        .name("Tom")
+        .money(Money.of(USD, 30))
+        .customerDao(customerDao)
+        .build();
+
+tom.save();
+
+// create products
+var productDao = new ProductDaoImpl(dataSource);
+
+var eggs =
+    Product.builder()
+        .name("Eggs")
+        .price(Money.of(USD, 10.0))
+        .expirationDate(LocalDate.now().plusDays(7))
+        .productDao(productDao)
+        .build();
+
+var butter =
+    Product.builder()
+        .name("Butter")
+        .price(Money.of(USD, 20.00))
+        .expirationDate(LocalDate.now().plusDays(9))
+        .productDao(productDao)
+        .build();
+
+var cheese =
+    Product.builder()
+        .name("Cheese")
+        .price(Money.of(USD, 25.0))
+        .expirationDate(LocalDate.now().plusDays(2))
+        .productDao(productDao)
+        .build();
+
+eggs.save();
+butter.save();
+cheese.save();
+
+// show money balance of customer after each purchase
+tom.showBalance();
+tom.showPurchases();
+
+// buy eggs
+tom.buyProduct(eggs);
+tom.showBalance();
+
+// buy butter
+tom.buyProduct(butter);
+tom.showBalance();
+
+// trying to buy cheese, but receive a refusal
+// because he didn't have enough money
+tom.buyProduct(cheese);
+tom.showBalance();
+
+// return butter and get money back
+tom.returnProduct(butter);
+tom.showBalance();
+
+// Tom can buy cheese now because he has enough money
+// and there is a discount on cheese because it expires in 2 days
+tom.buyProduct(cheese);
+
+tom.save();
+
+// show money balance and purchases after shopping
+tom.showBalance();
+tom.showPurchases();
+```
+
+The program output:
+
+```java
+17:52:28.690 [main] INFO com.iluwatar.domainmodel.Customer - Tom balance: USD 30.00
+17:52:28.695 [main] INFO com.iluwatar.domainmodel.Customer - Tom didn't bought anything
+17:52:28.699 [main] INFO com.iluwatar.domainmodel.Customer - Tom want to buy Eggs($10.00)...
+17:52:28.705 [main] INFO com.iluwatar.domainmodel.Customer - Tom bought Eggs!
+17:52:28.705 [main] INFO com.iluwatar.domainmodel.Customer - Tom balance: USD 20.00
+17:52:28.705 [main] INFO com.iluwatar.domainmodel.Customer - Tom want to buy Butter($20.00)...
+17:52:28.712 [main] INFO com.iluwatar.domainmodel.Customer - Tom bought Butter!
+17:52:28.712 [main] INFO com.iluwatar.domainmodel.Customer - Tom balance: USD 0.00
+17:52:28.712 [main] INFO com.iluwatar.domainmodel.Customer - Tom want to buy Cheese($20.00)...
+17:52:28.712 [main] ERROR com.iluwatar.domainmodel.Customer - Not enough money!
+17:52:28.712 [main] INFO com.iluwatar.domainmodel.Customer - Tom balance: USD 0.00
+17:52:28.712 [main] INFO com.iluwatar.domainmodel.Customer - Tom want to return Butter($20.00)...
+17:52:28.721 [main] INFO com.iluwatar.domainmodel.Customer - Tom returned Butter!
+17:52:28.721 [main] INFO com.iluwatar.domainmodel.Customer - Tom balance: USD 20.00
+17:52:28.721 [main] INFO com.iluwatar.domainmodel.Customer - Tom want to buy Cheese($20.00)...
+17:52:28.726 [main] INFO com.iluwatar.domainmodel.Customer - Tom bought Cheese!
+17:52:28.737 [main] INFO com.iluwatar.domainmodel.Customer - Tom balance: USD 0.00
+17:52:28.738 [main] INFO com.iluwatar.domainmodel.Customer - Tom bought: Eggs - $10.00, Cheese - $20.00
+```
+
+## Class diagram
+
+![](./etc/domain-model.urm.png "domain model")
+
+## Applicability
+
+Use a Domain model pattern when your domain logic is complex and that complexity can rapidly grow because this pattern handles increasing complexity very well. Otherwise, it's a more complex solution for organizing domain logic, so shouldn't use Domain Model pattern for systems with simple domain logic, because the cost of understanding it and complexity of data source exceeds the benefit of this pattern.
+
+## Related patterns
+
+- [Transaction Script](https://java-design-patterns.com/patterns/transaction-script/)
+
+- [Table Module](https://java-design-patterns.com/patterns/table-module/)
+  
+- [Service Layer](https://java-design-patterns.com/patterns/service-layer/)
+
+## Credits
+
+* [Domain Model Pattern](https://martinfowler.com/eaaCatalog/domainModel.html)
+* [Patterns of Enterprise Application Architecture](https://www.amazon.com/gp/product/0321127420/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=0321127420&linkId=18acc13ba60d66690009505577c45c04)
+* [Architecture patterns: domain model and friends](https://inviqa.com/blog/architecture-patterns-domain-model-and-friends)

domain-model/etc/domain-model.urm.puml

+@startuml
+package com.iluwatar.domainmodel {
+  class App {
+    + CREATE_SCHEMA_SQL : String {static}
+    + DELETE_SCHEMA_SQL : String {static}
+    + H2_DB_URL : String {static}
+    + App()
+    - createDataSource() : DataSource {static}
+    - createSchema(dataSource : DataSource) {static}
+    - deleteSchema(dataSource : DataSource) {static}
+    + main(args : String[]) {static}
+  }
+  class Customer {
+    - customerDao : CustomerDao
+    - money : Money
+    - name : String
+    - purchases : List<Product>
+    ~ Customer(customerDao : CustomerDao, purchases : List<Product>, name : String, money : Money)
+    + builder() : CustomerBuilder {static}
+    + buyProduct(product : Product)
+    + getCustomerDao() : CustomerDao
+    + getMoney() : Money
+    + getName() : String
+    + getPurchases() : List<Product>
+    - receiveMoney(amount : Money)
+    + returnProduct(product : Product)
+    + save()
+    + setMoney(money : Money)
+    + setName(name : String)
+    + setPurchases(purchases : List<Product>)
+    + showBalance()
+    + showPurchases()
+    - withdraw(amount : Money)
+  }
+  interface CustomerDao {
+    + addProduct(Product, Customer) {abstract}
+    + deleteProduct(Product, Customer) {abstract}
+    + findByName(String) : Optional<Customer> {abstract}
+    + save(Customer) {abstract}
+    + update(Customer) {abstract}
+  }
+  class CustomerDaoImpl {
+    - dataSource : DataSource
+    + CustomerDaoImpl(userDataSource : DataSource)
+    + addProduct(product : Product, customer : Customer)
+    + deleteProduct(product : Product, customer : Customer)
+    + findByName(name : String) : Optional<Customer>
+    + save(customer : Customer)
+    + update(customer : Customer)
+  }
+  class Product {
+    - expirationDate : LocalDate
+    - name : String
+    - price : Money
+    - productDao : ProductDao
+    + Product(productDao : ProductDao, name : String, price : Money, expirationDate : LocalDate)
+    + builder() : ProductBuilder {static}
+    - calculateDiscount() : Money
+    + getExpirationDate() : LocalDate
+    + getName() : String
+    + getPrice() : Money
+    + getProductDao() : ProductDao
+    + getSalePrice() : Money
+    + save()
+    + setExpirationDate(expirationDate : LocalDate)
+    + setName(name : String)
+    + setPrice(price : Money)
+  }
+  interface ProductDao {
+    + findByName(String) : Optional<Product> {abstract}
+    + save(Product) {abstract}
+    + update(Product) {abstract}
+  }
+  class ProductDaoImpl {
+    - dataSource : DataSource
+    + ProductDaoImpl(userDataSource : DataSource)
+    + findByName(name : String) : Optional<Product>
+    + save(product : Product)
+    + update(product : Product)
+  }
+}
+Product -->  ProductDao
+Customer -->  CustomerDao
+Customer -->  Product
+CustomerDaoImpl ..|> CustomerDao 
+ProductDaoImpl ..|> ProductDao 
+@enduml
\ No newline at end of file

domain-model/pom.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    The MIT License
+    Copyright © 2014-2021 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <artifactId>java-design-patterns</artifactId>
+        <groupId>com.iluwatar</groupId>
+        <version>1.25.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>domain-model</artifactId>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.h2database</groupId>
+            <artifactId>h2</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.joda</groupId>
+            <artifactId>joda-money</artifactId>
+            <version>1.0.1</version>
+        </dependency>
+    </dependencies>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <configuration>
+                            <archive>
+                                <manifest>
+                                    <mainClass>com.iluwatar.domainmodel.App</mainClass>
+                                </manifest>
+                            </archive>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>
\ No newline at end of file

domain-model/src/main/java/com/iluwatar/domainmodel/App.java

+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.domainmodel;
+
+import static org.joda.money.CurrencyUnit.USD;
+
+import java.sql.SQLException;
+import java.time.LocalDate;
+import javax.sql.DataSource;
+
+import org.h2.jdbcx.JdbcDataSource;
+import org.joda.money.Money;
+
+
+/**
+ * Domain Model pattern is a more complex solution for organizing domain logic than Transaction
+ * Script and Table Module. It provides an object-oriented way of dealing with complicated logic.
+ * Instead of having one procedure that handles all business logic for a user action like
+ * Transaction Script there are multiple objects and each of them handles a slice of domain logic
+ * that is relevant to it. The significant difference between Domain Model and Table Module pattern
+ * is that in Table Module a single class encapsulates all the domain logic for all records stored
+ * in table when in Domain Model every single class represents only one record in underlying table.
+ *
+ * <p>In this example, we will use the Domain Model pattern to implement buying of products
+ * by customers in a Shop. The main method will create a customer and a few products.
+ * Customer will do a few purchases, try to buy product which are too expensive for him,
+ * return product which he bought to return money.</p>
+ */
+public class App {
+
+  public static final String H2_DB_URL = "jdbc:h2:~/test";
+
+  public static final String CREATE_SCHEMA_SQL =
+      "CREATE TABLE CUSTOMERS (name varchar primary key, money decimal);"
+          + "CREATE TABLE PRODUCTS (name varchar primary key, price decimal, expiration_date date);"
+          + "CREATE TABLE PURCHASES ("
+          + "product_name varchar references PRODUCTS(name),"
+          + "customer_name varchar references CUSTOMERS(name));";
+
+  public static final String DELETE_SCHEMA_SQL =
+      "DROP TABLE CUSTOMERS IF EXISTS;"
+          + "DROP TABLE PURCHASES IF EXISTS;"
+          + "DROP TABLE PRODUCTS IF EXISTS;";
+
+  /**
+   * Program entry point.
+   *
+   * @param args command line arguments
+   * @throws Exception if any error occurs
+   */
+  public static void main(String[] args) throws Exception {
+
+    // Create data source and create the customers, products and purchases tables
+    final var dataSource = createDataSource();
+    deleteSchema(dataSource);
+    createSchema(dataSource);
+
+    // create customer
+    var customerDao = new CustomerDaoImpl(dataSource);
+
+    var tom =
+        Customer.builder()
+            .name("Tom")
+            .money(Money.of(USD, 30))
+            .customerDao(customerDao)
+            .build();
+
+    tom.save();
+
+    // create products
+    var productDao = new ProductDaoImpl(dataSource);
+
+    var eggs =
+        Product.builder()
+            .name("Eggs")
+            .price(Money.of(USD, 10.0))
+            .expirationDate(LocalDate.now().plusDays(7))
+            .productDao(productDao)
+            .build();
+
+    var butter =
+        Product.builder()
+            .name("Butter")
+            .price(Money.of(USD, 20.00))
+            .expirationDate(LocalDate.now().plusDays(9))
+            .productDao(productDao)
+            .build();
+
+    var cheese =
+        Product.builder()
+            .name("Cheese")
+            .price(Money.of(USD, 25.0))
+            .expirationDate(LocalDate.now().plusDays(2))
+            .productDao(productDao)
+            .build();
+
+    eggs.save();
+    butter.save();
+    cheese.save();
+
+    // show money balance of customer after each purchase
+    tom.showBalance();
+    tom.showPurchases();
+
+    // buy eggs
+    tom.buyProduct(eggs);
+    tom.showBalance();
+
+    // buy butter
+    tom.buyProduct(butter);
+    tom.showBalance();
+
+    // trying to buy cheese, but receive a refusal
+    // because he didn't have enough money
+    tom.buyProduct(cheese);
+    tom.showBalance();
+
+    // return butter and get money back
+    tom.returnProduct(butter);
+    tom.showBalance();
+
+    // Tom can buy cheese now because he has enough money
+    // and there is a discount on cheese because it expires in 2 days
+    tom.buyProduct(cheese);
+
+    tom.save();
+
+    // show money balance and purchases after shopping
+    tom.showBalance();
+    tom.showPurchases();
+  }
+
+  private static DataSource createDataSource() {
+    var dataSource = new JdbcDataSource();
+    dataSource.setUrl(H2_DB_URL);
+    return dataSource;
+  }
+
+  private static void deleteSchema(DataSource dataSource) throws SQLException {
+    try (var connection = dataSource.getConnection();
+        var statement = connection.createStatement()) {
+      statement.execute(DELETE_SCHEMA_SQL);
+    }
+  }
+
+  private static void createSchema(DataSource dataSource) throws SQLException {
+    try (var connection = dataSource.getConnection();
+        var statement = connection.createStatement()) {
+      statement.execute(CREATE_SCHEMA_SQL);
+    }
+  }
+}

domain-model/src/main/java/com/iluwatar/domainmodel/Customer.java

+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.domainmodel;
+
+import java.sql.SQLException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+
+import lombok.Builder;
+import lombok.Getter;
+import lombok.NonNull;
+import lombok.Setter;
+import lombok.extern.slf4j.Slf4j;
+import org.joda.money.Money;
+
+/**
+ * This class organizes domain logic of customer.
+ * A single instance of this class
+ * contains both the data and behavior of a single customer.
+ */
+@Slf4j
+@Getter
+@Setter
+@Builder
+public class Customer {
+
+  @NonNull private final CustomerDao customerDao;
+  @Builder.Default private List<Product> purchases = new ArrayList<>();
+  @NonNull private String name;
+  @NonNull private Money money;
+
+  /**
+   * Save customer or update if customer already exist.
+   */
+  public void save() {
+    try {
+      Optional<Customer> customer = customerDao.findByName(name);
+      if (customer.isPresent()) {
+        customerDao.update(this);
+      } else {
+        customerDao.save(this);
+      }
+    } catch (SQLException ex) {
+      LOGGER.error(ex.getMessage());
+    }
+  }
+
+  /**
+   * Add product to purchases, save to db and withdraw money.
+   *
+   * @param product to buy.
+   */
+  public void buyProduct(Product product) {
+    LOGGER.info(
+        String.format(
+            "%s want to buy %s($%.2f)...",
+            name, product.getName(), product.getSalePrice().getAmount()));
+    try {
+      withdraw(product.getSalePrice());
+    } catch (IllegalArgumentException ex) {
+      LOGGER.error(ex.getMessage());
+      return;
+    }
+    try {
+      customerDao.addProduct(product, this);
+      purchases.add(product);
+      LOGGER.info(String.format("%s bought %s!", name, product.getName()));
+    } catch (SQLException exception) {
+      receiveMoney(product.getSalePrice());
+      LOGGER.error(exception.getMessage());
+    }
+  }
+
+  /**
+   * Remove product from purchases, delete from db and return money.
+   *
+   * @param product to return.
+   */
+  public void returnProduct(Product product) {
+    LOGGER.info(
+        String.format(
+            "%s want to return %s($%.2f)...",
+            name, product.getName(), product.getSalePrice().getAmount()));
+    if (purchases.contains(product)) {
+      try {
+        customerDao.deleteProduct(product, this);
+        purchases.remove(product);
+        receiveMoney(product.getSalePrice());
+        LOGGER.info(String.format("%s returned %s!", name, product.getName()));
+      } catch (SQLException ex) {
+        LOGGER.error(ex.getMessage());
+      }
+    } else {
+      LOGGER.error(String.format("%s didn't buy %s...", name, product.getName()));
+    }
+  }
+
+  /**
+   * Print customer's purchases.
+   */
+  public void showPurchases() {
+    Optional<String> purchasesToShow =
+        purchases.stream()
+            .map(p -> p.getName() + " - $" + p.getSalePrice().getAmount())
+            .reduce((p1, p2) -> p1 + ", " + p2);
+
+    if (purchasesToShow.isPresent()) {
+      LOGGER.info(name + " bought: " + purchasesToShow.get());
+    } else {
+      LOGGER.info(name + " didn't bought anything");
+    }
+  }
+
+  /**
+   * Print customer's money balance.
+   */
+  public void showBalance() {
+    LOGGER.info(name + " balance: " + money);
+  }
+
+  private void withdraw(Money amount) throws IllegalArgumentException {
+    if (money.compareTo(amount) < 0) {
+      throw new IllegalArgumentException("Not enough money!");
+    }
+    money = money.minus(amount);
+  }
+
+  private void receiveMoney(Money amount) {
+    money = money.plus(amount);
+  }
+}

domain-model/src/main/java/com/iluwatar/domainmodel/CustomerDao.java

+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.domainmodel;
+
+import java.sql.SQLException;
+import java.util.Optional;
+
+public interface CustomerDao {
+
+  Optional<Customer> findByName(String name) throws SQLException;
+
+  void update(Customer customer) throws SQLException;
+
+  void save(Customer customer) throws SQLException;
+
+  void addProduct(Product product, Customer customer) throws SQLException;
+
+  void deleteProduct(Product product, Customer customer) throws SQLException;
+}

domain-model/src/main/java/com/iluwatar/domainmodel/CustomerDaoImpl.java

+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.domainmodel;
+
+import static org.joda.money.CurrencyUnit.USD;
+
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.util.Optional;
+import javax.sql.DataSource;
+
+import org.joda.money.Money;
+
+public class CustomerDaoImpl implements CustomerDao {
+
+  private final DataSource dataSource;
+
+  public CustomerDaoImpl(final DataSource userDataSource) {
+    this.dataSource = userDataSource;
+  }
+
+  @Override
+  public Optional<Customer> findByName(String name) throws SQLException {
+    var sql = "select * from CUSTOMERS where name = ?;";
+
+    try (var connection = dataSource.getConnection();
+        var preparedStatement = connection.prepareStatement(sql)) {
+      preparedStatement.setString(1, name);
+
+      ResultSet rs = preparedStatement.executeQuery();
+
+      if (rs.next()) {
+        return Optional.of(
+            Customer.builder()
+                .name(rs.getString("name"))
+                .money(Money.of(USD, rs.getBigDecimal("money")))
+                .customerDao(this)
+                .build());
+      } else {
+        return Optional.empty();
+      }
+    }
+  }
+
+  @Override
+  public void update(Customer customer) throws SQLException {
+    var sql = "update CUSTOMERS set money = ? where name = ?;";
+    try (var connection = dataSource.getConnection();
+        var preparedStatement = connection.prepareStatement(sql)) {
+      preparedStatement.setBigDecimal(1, customer.getMoney().getAmount());
+      preparedStatement.setString(2, customer.getName());
+      preparedStatement.executeUpdate();
+    }
+  }
+
+  @Override
+  public void save(Customer customer) throws SQLException {
+    var sql = "insert into CUSTOMERS (name, money) values (?, ?)";
+    try (var connection = dataSource.getConnection();
+        var preparedStatement = connection.prepareStatement(sql)) {
+      preparedStatement.setString(1, customer.getName());
+      preparedStatement.setBigDecimal(2, customer.getMoney().getAmount());
+      preparedStatement.executeUpdate();
+    }
+  }
+
+  @Override
+  public void addProduct(Product product, Customer customer) throws SQLException {
+    var sql = "insert into PURCHASES (product_name, customer_name) values (?,?)";
+    try (var connection = dataSource.getConnection();
+        var preparedStatement = connection.prepareStatement(sql)) {
+      preparedStatement.setString(1, product.getName());
+      preparedStatement.setString(2, customer.getName());
+      preparedStatement.executeUpdate();
+    }
+  }
+
+  @Override
+  public void deleteProduct(Product product, Customer customer) throws SQLException {
+    var sql = "delete from PURCHASES where product_name = ? and customer_name = ?";
+    try (var connection = dataSource.getConnection();
+        var preparedStatement = connection.prepareStatement(sql)) {
+      preparedStatement.setString(1, product.getName());
+      preparedStatement.setString(2, customer.getName());
+      preparedStatement.executeUpdate();
+    }
+  }
+}

domain-model/src/main/java/com/iluwatar/domainmodel/Product.java

+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.domainmodel;
+
+import static org.joda.money.CurrencyUnit.USD;
+
+import java.math.RoundingMode;
+import java.sql.SQLException;
+import java.time.LocalDate;
+import java.time.temporal.ChronoUnit;
+import java.util.Optional;
+
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Getter;
+import lombok.NonNull;
+import lombok.Setter;
+import lombok.extern.slf4j.Slf4j;
+import org.joda.money.Money;
+
+/**
+ * This class organizes domain logic of product.
+ * A single instance of this class
+ * contains both the data and behavior of a single product.
+ */
+@Slf4j
+@Getter
+@Setter
+@Builder
+@AllArgsConstructor
+public class Product {
+
+  private static final int DAYS_UNTIL_EXPIRATION_WHEN_DISCOUNT_ACTIVE = 4;
+  private static final double DISCOUNT_RATE = 0.2;
+
+  @NonNull private final ProductDao productDao;
+  @NonNull private String name;
+  @NonNull private Money price;
+  @NonNull private LocalDate expirationDate;
+
+  /**
+   * Save product or update if product already exist.
+   */
+  public void save() {
+    try {
+      Optional<Product> product = productDao.findByName(name);
+      if (product.isPresent()) {
+        productDao.update(this);
+      } else {
+        productDao.save(this);
+      }
+    } catch (SQLException ex) {
+      LOGGER.error(ex.getMessage());
+    }
+  }
+
+  /**
+   * Calculate sale price of product with discount.
+   */
+  public Money getSalePrice() {
+    return price.minus(calculateDiscount());
+  }
+
+  private Money calculateDiscount() {
+    if (ChronoUnit.DAYS.between(LocalDate.now(), expirationDate)
+            < DAYS_UNTIL_EXPIRATION_WHEN_DISCOUNT_ACTIVE) {
+
+      return price.multipliedBy(DISCOUNT_RATE, RoundingMode.DOWN);
+    }
+
+    return Money.zero(USD);
+  }
+}

domain-model/src/main/java/com/iluwatar/domainmodel/ProductDao.java

+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.domainmodel;
+
+import java.sql.SQLException;
+import java.util.Optional;
+
+public interface ProductDao {
+
+  Optional<Product> findByName(String name) throws SQLException;
+
+  void save(Product product) throws SQLException;
+
+  void update(Product product) throws SQLException;
+}

domain-model/src/main/java/com/iluwatar/domainmodel/ProductDaoImpl.java

+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.domainmodel;
+
+import static org.joda.money.CurrencyUnit.USD;
+
+import java.sql.Date;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.util.Optional;
+import javax.sql.DataSource;
+
+import org.joda.money.Money;
+
+
+public class ProductDaoImpl implements ProductDao {
+
+  private final DataSource dataSource;
+
+  public ProductDaoImpl(final DataSource userDataSource) {
+    this.dataSource = userDataSource;
+  }
+
+  @Override
+  public Optional<Product> findByName(String name) throws SQLException {
+    var sql = "select * from PRODUCTS where name = ?;";
+
+    try (var connection = dataSource.getConnection();
+        var preparedStatement = connection.prepareStatement(sql)) {
+      preparedStatement.setString(1, name);
+
+      ResultSet rs = preparedStatement.executeQuery();
+
+      if (rs.next()) {
+        return Optional.of(
+            Product.builder()
+                .name(rs.getString("name"))
+                .price(Money.of(USD, rs.getBigDecimal("price")))
+                .expirationDate(rs.getDate("expiration_date").toLocalDate())
+                .productDao(this)
+                .build());
+      } else {
+        return Optional.empty();
+      }
+    }
+  }
+
+  @Override
+  public void save(Product product) throws SQLException {
+    var sql = "insert into PRODUCTS (name, price, expiration_date) values (?, ?, ?)";
+    try (var connection = dataSource.getConnection();
+        var preparedStatement = connection.prepareStatement(sql)) {
+      preparedStatement.setString(1, product.getName());
+      preparedStatement.setBigDecimal(2, product.getPrice().getAmount());
+      preparedStatement.setDate(3, Date.valueOf(product.getExpirationDate()));
+      preparedStatement.executeUpdate();
+    }
+  }
+
+  @Override
+  public void update(Product product) throws SQLException {
+    var sql = "update PRODUCTS set price = ?, expiration_date = ? where name = ?;";
+    try (var connection = dataSource.getConnection();
+        var preparedStatement = connection.prepareStatement(sql)) {
+      preparedStatement.setBigDecimal(1, product.getPrice().getAmount());
+      preparedStatement.setDate(2, Date.valueOf(product.getExpirationDate()));
+      preparedStatement.setString(3, product.getName());
+      preparedStatement.executeUpdate();
+    }
+  }
+}

domain-model/src/test/java/com/iluwatar/domainmodel/AppTest.java

+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.domainmodel;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+/** Tests that Domain Model example runs without errors. */
+final class AppTest {
+
+  @Test
+  void shouldExecuteApplicationWithoutException() {
+    assertDoesNotThrow(() -> App.main(new String[] {}));
+  }
+
+}

domain-model/src/test/java/com/iluwatar/domainmodel/CustomerDaoImplTest.java

+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.domainmodel;
+
+import org.joda.money.CurrencyUnit;
+import org.joda.money.Money;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import javax.sql.DataSource;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.time.LocalDate;
+
+import static org.joda.money.CurrencyUnit.USD;
+import static org.junit.jupiter.api.Assertions.*;
+
+class CustomerDaoImplTest {
+
+  public static final String INSERT_CUSTOMER_SQL = "insert into CUSTOMERS values('customer', 100)";
+  public static final String SELECT_CUSTOMERS_SQL = "select name, money from CUSTOMERS";
+  public static final String INSERT_PURCHASES_SQL =
+      "insert into PURCHASES values('product', 'customer')";
+  public static final String SELECT_PURCHASES_SQL =
+      "select product_name, customer_name from PURCHASES";
+
+  private DataSource dataSource;
+  private Product product;
+  private Customer customer;
+  private CustomerDao customerDao;
+
+  @BeforeEach
+  void setUp() throws SQLException {
+    // create db schema
+    dataSource = TestUtils.createDataSource();
+
+    TestUtils.deleteSchema(dataSource);
+    TestUtils.createSchema(dataSource);
+
+    // setup objects
+    customerDao = new CustomerDaoImpl(dataSource);
+
+    customer = Customer.builder().name("customer").money(Money.of(CurrencyUnit.USD,100.0)).customerDao(customerDao).build();
+
+    product =
+        Product.builder()
+            .name("product")
+            .price(Money.of(USD, 100.0))
+            .expirationDate(LocalDate.parse("2021-06-27"))
+            .productDao(new ProductDaoImpl(dataSource))
+            .build();
+  }
+
+  @AfterEach
+  void tearDown() throws SQLException {
+    TestUtils.deleteSchema(dataSource);
+  }
+
+  @Test
+  void shouldFindCustomerByName() throws SQLException {
+    var customer = customerDao.findByName("customer");
+
+    assertTrue(customer.isEmpty());
+
+    TestUtils.executeSQL(INSERT_CUSTOMER_SQL, dataSource);
+
+    customer = customerDao.findByName("customer");
+
+    assertTrue(customer.isPresent());
+    assertEquals("customer", customer.get().getName());
+    assertEquals(Money.of(USD, 100), customer.get().getMoney());
+  }
+
+  @Test
+  void shouldSaveCustomer() throws SQLException {
+    customerDao.save(customer);
+
+    try (var connection = dataSource.getConnection();
+        var statement = connection.createStatement();
+        ResultSet rs = statement.executeQuery(SELECT_CUSTOMERS_SQL)) {
+
+      assertTrue(rs.next());
+      assertEquals(customer.getName(), rs.getString("name"));
+      assertEquals(customer.getMoney(), Money.of(USD, rs.getBigDecimal("money")));
+    }
+
+    assertThrows(SQLException.class, () -> customerDao.save(customer));
+  }
+
+  @Test
+  void shouldUpdateCustomer() throws SQLException {
+    TestUtils.executeSQL(INSERT_CUSTOMER_SQL, dataSource);
+
+    customer.setMoney(Money.of(CurrencyUnit.USD, 99));
+
+    customerDao.update(customer);
+
+    try (var connection = dataSource.getConnection();
+        var statement = connection.createStatement();
+        ResultSet rs = statement.executeQuery(SELECT_CUSTOMERS_SQL)) {
+
+      assertTrue(rs.next());
+      assertEquals(customer.getName(), rs.getString("name"));
+      assertEquals(customer.getMoney(), Money.of(USD, rs.getBigDecimal("money")));
+      assertFalse(rs.next());
+    }
+  }
+
+  @Test
+  void shouldAddProductToPurchases() throws SQLException {
+    TestUtils.executeSQL(INSERT_CUSTOMER_SQL, dataSource);
+    TestUtils.executeSQL(ProductDaoImplTest.INSERT_PRODUCT_SQL, dataSource);
+
+    customerDao.addProduct(product, customer);
+
+    try (var connection = dataSource.getConnection();
+        var statement = connection.createStatement();
+        ResultSet rs = statement.executeQuery(SELECT_PURCHASES_SQL)) {
+
+      assertTrue(rs.next());
+      assertEquals(product.getName(), rs.getString("product_name"));
+      assertEquals(customer.getName(), rs.getString("customer_name"));
+      assertFalse(rs.next());
+    }
+  }
+
+  @Test
+  void shouldDeleteProductFromPurchases() throws SQLException {
+    TestUtils.executeSQL(INSERT_CUSTOMER_SQL, dataSource);
+    TestUtils.executeSQL(ProductDaoImplTest.INSERT_PRODUCT_SQL, dataSource);
+    TestUtils.executeSQL(INSERT_PURCHASES_SQL, dataSource);
+
+    customerDao.deleteProduct(product, customer);
+
+    try (var connection = dataSource.getConnection();
+        var statement = connection.createStatement();
+        ResultSet rs = statement.executeQuery(SELECT_PURCHASES_SQL)) {
+
+      assertFalse(rs.next());
+    }
+  }
+}

domain-model/src/test/java/com/iluwatar/domainmodel/CustomerTest.java

+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.domainmodel;
+
+import org.joda.money.CurrencyUnit;
+import org.joda.money.Money;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.sql.SQLException;
+import java.time.LocalDate;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Optional;
+
+import static org.joda.money.CurrencyUnit.USD;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.*;
+
+class CustomerTest {
+
+    private CustomerDao customerDao;
+    private Customer customer;
+    private Product product;
+
+    @BeforeEach
+    void setUp() {
+        customerDao = mock(CustomerDao.class);
+
+        customer = Customer.builder()
+                .name("customer")
+                .money(Money.of(CurrencyUnit.USD, 100.0))
+                .customerDao(customerDao)
+                .build();
+
+        product = Product.builder()
+                .name("product")
+                .price(Money.of(USD, 100.0))
+                .expirationDate(LocalDate.now().plusDays(10))
+                .productDao(mock(ProductDao.class))
+                .build();
+    }
+
+    @Test
+    void shouldSaveCustomer() throws SQLException {
+        when(customerDao.findByName("customer")).thenReturn(Optional.empty());
+
+        customer.save();
+
+        verify(customerDao, times(1)).save(customer);
+
+        when(customerDao.findByName("customer")).thenReturn(Optional.of(customer));
+
+        customer.save();
+
+        verify(customerDao, times(1)).update(customer);
+    }
+
+    @Test
+    void shouldAddProductToPurchases() {
+        product.setPrice(Money.of(USD, 200.0));
+
+        customer.buyProduct(product);
+
+        assertEquals(customer.getPurchases(), new ArrayList<>());
+        assertEquals(customer.getMoney(), Money.of(USD,100));
+
+        product.setPrice(Money.of(USD, 100.0));
+
+        customer.buyProduct(product);
+
+        assertEquals(new ArrayList<>(Arrays.asList(product)), customer.getPurchases());
+        assertEquals(Money.zero(USD), customer.getMoney());
+    }
+
+    @Test
+    void shouldRemoveProductFromPurchases() {
+        customer.setPurchases(new ArrayList<>(Arrays.asList(product)));
+
+        customer.returnProduct(product);
+
+        assertEquals(new ArrayList<>(), customer.getPurchases());
+        assertEquals(Money.of(USD, 200), customer.getMoney());
+
+        customer.returnProduct(product);
+
+        assertEquals(new ArrayList<>(), customer.getPurchases());
+        assertEquals(Money.of(USD, 200), customer.getMoney());
+    }
+}
+

domain-model/src/test/java/com/iluwatar/domainmodel/ProductDaoImplTest.java

+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.domainmodel;
+
+import org.joda.money.Money;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import javax.sql.DataSource;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.time.LocalDate;
+
+import static org.joda.money.CurrencyUnit.USD;
+import static org.junit.jupiter.api.Assertions.*;
+
+class ProductDaoImplTest {
+
+    public static final String INSERT_PRODUCT_SQL =
+            "insert into PRODUCTS values('product', 100, DATE '2021-06-27')";
+    public static final String SELECT_PRODUCTS_SQL =
+            "select name, price, expiration_date from PRODUCTS";
+
+    private DataSource dataSource;
+    private ProductDao productDao;
+    private Product product;
+
+    @BeforeEach
+    void setUp() throws SQLException {
+        // create schema
+        dataSource = TestUtils.createDataSource();
+
+        TestUtils.deleteSchema(dataSource);
+        TestUtils.createSchema(dataSource);
+
+        // setup objects
+        productDao = new ProductDaoImpl(dataSource);
+
+        product =
+                Product.builder()
+                        .name("product")
+                        .price(Money.of(USD, 100.0))
+                        .expirationDate(LocalDate.parse("2021-06-27"))
+                        .productDao(productDao)
+                        .build();
+    }
+
+    @AfterEach
+    void tearDown() throws SQLException {
+        TestUtils.deleteSchema(dataSource);
+    }
+
+    @Test
+    void shouldFindProductByName() throws SQLException {
+        var product = productDao.findByName("product");
+
+        assertTrue(product.isEmpty());
+
+        TestUtils.executeSQL(INSERT_PRODUCT_SQL, dataSource);
+
+        product = productDao.findByName("product");
+
+        assertTrue(product.isPresent());
+        assertEquals("product", product.get().getName());
+        assertEquals(Money.of(USD, 100), product.get().getPrice());
+        assertEquals(LocalDate.parse("2021-06-27"), product.get().getExpirationDate());
+    }
+
+    @Test
+    void shouldSaveProduct() throws SQLException {
+
+        productDao.save(product);
+
+        try (var connection = dataSource.getConnection();
+             var statement = connection.createStatement();
+             ResultSet rs = statement.executeQuery(SELECT_PRODUCTS_SQL)) {
+
+            assertTrue(rs.next());
+            assertEquals(product.getName(), rs.getString("name"));
+            assertEquals(product.getPrice(), Money.of(USD, rs.getBigDecimal("price")));
+            assertEquals(product.getExpirationDate(), rs.getDate("expiration_date").toLocalDate());
+        }
+
+        assertThrows(SQLException.class, () -> productDao.save(product));
+    }
+
+    @Test
+    void shouldUpdateProduct() throws SQLException {
+        TestUtils.executeSQL(INSERT_PRODUCT_SQL, dataSource);
+
+        product.setPrice(Money.of(USD, 99.0));
+
+        productDao.update(product);
+
+        try (var connection = dataSource.getConnection();
+             var statement = connection.createStatement();
+             ResultSet rs = statement.executeQuery(SELECT_PRODUCTS_SQL)) {
+
+            assertTrue(rs.next());
+            assertEquals(product.getName(), rs.getString("name"));
+            assertEquals(product.getPrice(), Money.of(USD, rs.getBigDecimal("price")));
+            assertEquals(product.getExpirationDate(), rs.getDate("expiration_date").toLocalDate());
+        }
+    }
+}

domain-model/src/test/java/com/iluwatar/domainmodel/ProductTest.java

+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.domainmodel;
+
+import org.joda.money.Money;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.sql.SQLException;
+import java.time.LocalDate;
+import java.util.Optional;
+
+import static org.joda.money.CurrencyUnit.USD;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.*;
+
+class ProductTest {
+
+    private ProductDao productDao;
+    private Product product;
+
+    @BeforeEach
+    void setUp() {
+        productDao = mock(ProductDaoImpl.class);
+
+        product = Product.builder()
+                .name("product")
+                .price(Money.of(USD, 100.0))
+                .expirationDate(LocalDate.now().plusDays(10))
+                .productDao(productDao)
+                .build();
+    }
+
+    @Test
+    void shouldSaveProduct() throws SQLException {
+        when(productDao.findByName("product")).thenReturn(Optional.empty());
+
+        product.save();
+
+        verify(productDao, times(1)).save(product);
+
+        when(productDao.findByName("product")).thenReturn(Optional.of(product));
+
+        product.save();
+
+        verify(productDao, times(1)).update(product);
+    }
+
+    @Test
+    void shouldGetSalePriceOfProduct() {
+        assertEquals(Money.of(USD, 100), product.getSalePrice());
+
+        product.setExpirationDate(LocalDate.now().plusDays(2));
+
+        assertEquals(Money.of(USD, 80), product.getSalePrice());
+    }
+}

domain-model/src/test/java/com/iluwatar/domainmodel/TestUtils.java

+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.domainmodel;
+
+import org.h2.jdbcx.JdbcDataSource;
+
+import javax.sql.DataSource;
+import java.sql.SQLException;
+
+public class TestUtils {
+
+  public static void executeSQL( String sql, DataSource dataSource) throws SQLException {
+    try (var connection = dataSource.getConnection();
+        var statement = connection.createStatement()) {
+      statement.executeUpdate(sql);
+    }
+  }
+
+  public static void createSchema(DataSource dataSource) throws SQLException {
+    TestUtils.executeSQL(App.CREATE_SCHEMA_SQL, dataSource);
+  }
+
+  public static void deleteSchema(DataSource dataSource) throws SQLException {
+    TestUtils.executeSQL(App.DELETE_SCHEMA_SQL, dataSource);
+  }
+
+  public static DataSource createDataSource() {
+    var dataSource = new JdbcDataSource();
+    dataSource.setURL(App.H2_DB_URL);
+    return dataSource;
+  }
+}

pom.xml

@@ -232,6 +232,7 @@
         <module>table-module</module>
         <module>presentation</module>
         <module>lockable-object</module>
+        <module>domain-model</module>
     </modules>
 
     <repositories>
@@ -379,12 +380,12 @@
                 <version>${system-lambda.version}</version>
                 <scope>test</scope>
             </dependency>
-		    <dependency>
-			    <groupId>commons-io</groupId>
-			    <artifactId>commons-io</artifactId>
-			    <version>${commons-io.version}</version>
-		        </dependency>
-            </dependencies>
+            <dependency>
+                <groupId>commons-io</groupId>
+                <artifactId>commons-io</artifactId>
+                <version>${commons-io.version}</version>
+            </dependency>
+        </dependencies>
     </dependencyManagement>
     <dependencies>
         <dependency>

strategy/pom.xml

@@ -59,7 +59,7 @@
             <configuration>
               <archive>
                 <manifest>
-                  <mainClass>com.iluwatar.subclasssandbox.App</mainClass>
+                  <mainClass>com.iluwatar.strategy.App</mainClass>
                 </manifest>
               </archive>
             </configuration>

table-module/README.md

@@ -125,7 +125,7 @@ Use the Table Module Pattern when
 
 - [Transaction Script](https://java-design-patterns.com/patterns/transaction-script/)
 
-- Domain Model
+- [Domain Model](https://java-design-patterns.com/patterns/domain-model/)
 
 ## Credits