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>> user.articles => [#<Article id: 6, >] >> user.articles << Article.new(:title => 'One-to-many associations', :body => 'One-to-many associations describe a pattern ..') => [#<Article id: 6, >, #<Article id: 7, >] >> user.article_ids => [6, 7] >> user.articles.first => #<Article id: 6, > >> user.articles.clear => [] >> user.articles.count => 0 >> Article.count => 2 >> user.articles.create :title => 'Associations', :body => 'Active Record makes working with associations easy..' => #<Article id: 8, > You can also pass in options to your association declaration to affect the way you work with those associations. Table 5-5 lists some of the most common options. Table 5-5. Common has_many Options
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Specifies the class name of the association. Used when the class name can t be inferred from the association name. Specifies the conditions that the associated objects must meet in order to be included as a WHERE SQL fragment. Specifies the foreign key used for the association in the event that it doesn t adhere to convention of being the lowercase, singular name of target class with _id appended. Specifies the order in which the associated objects are returned as an ORDER BY SQL fragment. Specifies that the associated objects should be removed when this object is. If set to :destroy, the associated objects are deleted using the destroy method. If set to :delete, the associated objects are deleted without calling their destroy method. If set to :nullify, the associated objects foreign keys are set to NULL.
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has_many :articles, :class_name => 'Post'
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has_many :articles, :conditions => "active = 1"
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:foreign_key
has_many :articles, :foreign_key => 'post_id'
:order
has_many :articles, :order => "published_at DESC"
:dependent
has_many :articles, :dependent => :destroy
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There s much more to has_many associations than can possibly be covered here, so be sure to check out the Rails API documentation (http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#M001833) for the full scoop.
Applying Association Options
It s time to apply what you ve learned to your domain model. Specifically, you use the :order option to apply a default order to the User.has_many :articles declaration, and you use the :dependent option to make sure when you delete a user, all their articles are deleted as well.
Specifying a Default Order
When you access a user s articles, you want to make sure they come back in the order in which they ve been published. Specifically, you want the oldest to be at the bottom of the list and the furthest in the future to be at the top. You can do this by configuring the has_many association with a default order using the :order option. Add the :order option to the has_many :articles declaration, as shown in Listing 5-8. Listing 5-8. :order Option Added to has_many: http://gist.github.com/324010 class User < ActiveRecord::Base has_one :profile has_many :articles, :order => 'published_at DESC' end You give the name of the field that you want to order by, and then you say either ASC (ascending) or DESC (descending) to indicate the order in which the results should be returned. Because time moves forward (to bigger numbers), you want to make sure you re going back in time, so you use the DESC keyword here.
NOTE ASC and DESC are SQL keywords. You re actually specifying a SQL fragment here, as discussed in the Advanced Finding section later in this chapter.
You can also specify a secondary order by adding a comma between arguments. Let s say you wanted to sort by the title of the article after you sort by the date. If two articles have been published on the same day, they are ordered first by the date and then by the lexical order of the title. Listing 5-9 shows the article title added to the :order option. Listing 5-9. Adding the Title to the :order Option for has_many: http://gist.github.com/324019 class User < ActiveRecord::Base has_one :profile has_many :articles, :order => 'published_at DESC, title ASC' end
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