@@ -9,6 +9,7 @@ After reading this guide, you will know:
* How to specify the order, retrieved attributes, grouping, and other properties of the found records.
* How to use eager loading to reduce the number of database queries needed for data retrieval.
* How to use dynamic finders methods.
* How to use method chaining to use multiple ActiveRecord methods together.
* How to check for the existence of particular records.
* How to perform various calculations on Active Record models.
* How to run EXPLAIN on relations.
...
...
@@ -1327,6 +1328,40 @@ You can specify an exclamation point (`!`) on the end of the dynamic finders to
If you want to find both by name and locked, you can chain these finders together by simply typing "`and`" between the fields. For example, `Client.find_by_first_name_and_locked("Ryan", true)`.
Understanding The Method Chaining
---------------------------------
The ActiveRecord pattern implements [Method Chaining](http://en.wikipedia.org/wiki/Method_chaining).
This allow us to use multiple ActiveRecord methods in a simple and straightforward way.
You can chain a method in a sentence when the previous method called returns `ActiveRecord::Relation`,
like `all`, `where`, and `joins`. Methods that returns a instance of a single object
(see [Retrieving a Single Object Section](#retrieving-a-single-object)) have to be be the last
in the sentence.
This guide won't cover all the possibilities, just a few as example.
### Retrieving filtered data from multiple tables
```ruby
Person
.select('people.id, people.name, comments.text')
.joins(:comments)
.where('comments.create_at > ?',1.week.ago)
```
### Retrieving specific data from multiple tables
```ruby
Person
.select('people.id, people.name, companies.name')
.joins(:company)
.find_by('people.name'=>'John')# this should be the last
```
NOTE: Remember that, if `find_by` return more than one registry, it will take just the first
