The **DataShare** module allows an application to manage its own data and share data with other applications. Currently, data can be shared only between applications on the same device.
## Available APIs
**Table 1** APIs of the data provider
|API|Description|
|:------|:------|
|onCreate?(want: Want, callback: AsyncCallback<void>): void|Called to initialize service logic when the data provider application is created, for example, when a database is created.|
|insert?(uri: string, valueBucket: ValuesBucket, callback: AsyncCallback<number>): void|Inserts data into the database.|
|update?(uri: string, predicates: DataSharePredicates, valueBucket: ValuesBucket, callback: AsyncCallback<number>): void|Updates data in the database.|
|query?(uri: string, predicates: DataSharePredicates, columns: Array<string>, callback: AsyncCallback<Object>): void|Queries data from the database.|
|delete?(uri: string, predicates: DataSharePredicates, callback: AsyncCallback<number>): void|Deletes data from the database.|
For more details, see [DataShareExtensionAbility](../reference/apis/js-apis-application-DataShareExtensionAbility.md).
| insert(uri: string, value: ValuesBucket, callback: AsyncCallback<number>): void | Inserts a single data record into the database. |
| update(uri: string, predicates: DataSharePredicates, value: ValuesBucket, callback: AsyncCallback<number>): void | Updates data in the database. |
| query(uri: string, predicates: DataSharePredicates, columns: Array<string>, callback: AsyncCallback<DataShareResultSet>): void | Queries data from the database. |
| delete(uri: string, predicates: DataSharePredicates, callback: AsyncCallback<number>): void | Deletes one or more data records from the database.|
For more details, see [DataShareHelper](../reference/apis/js-apis-data-dataShare.md).
## When to Use
There are two roles in **DataShare**.
- Data provider: adds, deletes, modifies, and queries data, opens files, and shares data.
- Data consumer: accesses the data provided by the provider using **DataShareHelper**.
Examples are given below.
### Data Provider Application Development (Only for System Applications)
2. Override **DataShareExtensionAbility** APIs based on actual requirements. For example, if the data provider provides only data query, override only the **query()** API.
3. Implement the data provider services. For example, implement data storage of the data provider by using a database, reading and writing files, or accessing the network.
```ts
letDB_NAME="DB00.db";
letTBL_NAME="TBL00";
letDDL_TBL_CREATE="CREATE TABLE IF NOT EXISTS "
+TBL_NAME
+" (id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, age INTEGER, isStudent BOOLEAN, Binary BINARY)";
2. Define the URI string for communicating with the data provider.
```ts
// Different from the URI defined in the module.json5 file, the URI passed in the parameter has an extra slash (/), because there is a DeviceID parameter between the second and the third slash (/).
3. Use the APIs provided by **DataShareHelper** to access the services provided by the provider, for example, adding, deleting, modifying, and querying data.
The **DataShare** module allows an application to manage its own data and share data with other applications. Currently, data can be shared only between applications on the same device.
Data needs to be shared in a wealth of scenarios. For example, contacts, short message service (SMS), and media gallery always needs to be shared. However, certain data, such as accounts and passwords, cannot be shared. Some data, such as SMS messages, can be queried but not modified by other applications. **DataShare** provides a secure data sharing mechanism for applications in a variety of scenarios.
The data provider can directly use the **DataShare** framework to share data with other applications without complex encapsulation. The data consumer only needs to learn and use a set of interfaces because the data access mode does not vary with the data provisioning mode. This greatly reduces the learning time and development difficulty.
## Basic Concepts
Before you get started, familiarize yourself with the following concepts:
- Data provider
An application that provides data and implements related services. It is also called a producer or server.
- Data consumer
An application that accesses the data or services provided by a data provider. It is also called a client.
- Value bucket (**ValuesBucket**)
One or more data records stored in the form of key-value (KV) pairs. The keys are of the string type. The values can be of the number, string, Boolean, or Unit8Array type.
- Result set
A collection of query results. Flexible data access modes are provided for users to obtain data.
- Predicate
Conditions specified for updating, deleting, or querying data in the database.
## Working Principles
**Figure 1** DataShare mechanism
- The **DataShareExtAbility** module, as the data provider, implements data sharing between applications.
- The **DataShareHelper** module, as the data consumer, provides interfaces for accessing data, including adding, deleting, modifying, and querying data.
- The data consumer communicates with the data provider using inter-process communication (IPC). The data provider can be implemented through a database or other data storage.
- The **ResultSet** module is implemented through shared memory. Shared memory stores the result sets, and interfaces are provided to traverse result sets.
## Constraints
-**DataShare** is subject to the limitations on the database used by the data provider. For example, the supported data models, length of the keys and values, and maximum number of databases that can be accessed at a time by each application vary with the database in use.
- The payloads of **ValuesBucket**, predicates, and result sets are restricted by IPC.
