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diff --git a/guides/source/active_record_querying.md b/guides/source/active_record_querying.md index e1a465c64f..f6fbc29707 100644 --- a/guides/source/active_record_querying.md +++ b/guides/source/active_record_querying.md @@ -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. @@ -1327,10 +1328,44 @@ 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 +and ignore the others. + Find or Build a New Object -------------------------- -NOTE: Some dynamic finders have been deprecated in Rails 4.0 and will be +NOTE: Some dynamic finders were deprecated in Rails 4.0 and removed in Rails 4.1. The best practice is to use Active Record scopes instead. You can find the deprecation gem at https://github.com/rails/activerecord-deprecated_finders |