diff options
Diffstat (limited to 'activerecord/lib/active_record/associations.rb')
| -rw-r--r-- | activerecord/lib/active_record/associations.rb | 71 |
1 files changed, 59 insertions, 12 deletions
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb index d3b9b8251a..4ec1c8d545 100644 --- a/activerecord/lib/active_record/associations.rb +++ b/activerecord/lib/active_record/associations.rb @@ -447,9 +447,11 @@ module ActiveRecord # # Possible callbacks are: +before_add+, +after_add+, +before_remove+ and +after_remove+. # - # Should any of the +before_add+ callbacks throw an exception, the object does not get - # added to the collection. Same with the +before_remove+ callbacks; if an exception is - # thrown the object doesn't get removed. + # If any of the +before_add+ callbacks throw an exception, the object will not be + # added to the collection. + # + # Similarly, if any of the +before_remove+ callbacks throw an exception, the object + # will not be removed from the collection. # # == Association extensions # @@ -647,7 +649,7 @@ module ActiveRecord # belongs_to :commenter # end # - # When using nested association, you will not be able to modify the association because there + # When using a nested association, you will not be able to modify the association because there # is not enough information to know what modification to make. For example, if you tried to # add a <tt>Commenter</tt> in the example above, there would be no way to tell how to set up the # intermediate <tt>Post</tt> and <tt>Comment</tt> objects. @@ -717,7 +719,7 @@ module ActiveRecord # == Eager loading of associations # # Eager loading is a way to find objects of a certain class and a number of named associations. - # This is one of the easiest ways of to prevent the dreaded N+1 problem in which fetching 100 + # It is one of the easiest ways to prevent the dreaded N+1 problem in which fetching 100 # posts that each need to display their author triggers 101 database queries. Through the # use of eager loading, the number of queries will be reduced from 101 to 2. # @@ -749,16 +751,16 @@ module ActiveRecord # Post.includes(:author, :comments).each do |post| # # This will load all comments with a single query. This reduces the total number of queries - # to 3. More generally the number of queries will be 1 plus the number of associations + # to 3. In general, the number of queries will be 1 plus the number of associations # named (except if some of the associations are polymorphic +belongs_to+ - see below). # # To include a deep hierarchy of associations, use a hash: # - # Post.includes(:author, {comments: {author: :gravatar}}).each do |post| + # Post.includes(:author, { comments: { author: :gravatar } }).each do |post| # - # That'll grab not only all the comments but all their authors and gravatar pictures. - # You can mix and match symbols, arrays and hashes in any combination to describe the - # associations you want to load. + # The above code will load all the comments and all of their associated + # authors and gravatars. You can mix and match any combination of symbols, + # arrays, and hashes to retrieve the associations you want to load. # # All of this power shouldn't fool you into thinking that you can pull out huge amounts # of data with no performance penalty just because you've reduced the number of queries. @@ -767,8 +769,8 @@ module ActiveRecord # cut down on the number of queries in a situation as the one described above. # # Since only one table is loaded at a time, conditions or orders cannot reference tables - # other than the main one. If this is the case Active Record falls back to the previously - # used LEFT OUTER JOIN based strategy. For example + # other than the main one. If this is the case, Active Record falls back to the previously + # used LEFT OUTER JOIN based strategy. For example: # # Post.includes([:author, :comments]).where(['comments.approved = ?', true]) # @@ -1133,6 +1135,17 @@ module ActiveRecord # * <tt>Firm#clients.create!</tt> (similar to <tt>c = Client.new("firm_id" => id); c.save!</tt>) # The declaration can also include an +options+ hash to specialize the behavior of the association. # + # === Scopes + # + # You can pass a second argument +scope+ as a callable (i.e. proc or + # lambda) to retrieve a specific set of records or customize the generated + # query when you access the associated collection. + # + # Scope examples: + # has_many :comments, -> { where(author_id: 1) } + # has_many :employees, -> { joins(:address) } + # has_many :posts, ->(post) { where("max_post_length > ?", post.length) } + # # === Options # [:class_name] # Specify the class name of the association. Use it only if that name can't be inferred @@ -1257,6 +1270,17 @@ module ActiveRecord # * <tt>Account#create_beneficiary</tt> (similar to <tt>b = Beneficiary.new("account_id" => id); b.save; b</tt>) # * <tt>Account#create_beneficiary!</tt> (similar to <tt>b = Beneficiary.new("account_id" => id); b.save!; b</tt>) # + # === Scopes + # + # You can pass a second argument +scope+ as a callable (i.e. proc or + # lambda) to retrieve a specific record or customize the generated query + # when you access the associated object. + # + # Scope examples: + # has_one :auther, -> { where(comment_id: 1) } + # has_one :employer, -> { joins(:company) } + # has_one :dob, ->(dob) { where("Date.new(2000, 01, 01) > ?", dob) } + # # === Options # # The declaration can also include an +options+ hash to specialize the behavior of the association. @@ -1366,6 +1390,17 @@ module ActiveRecord # * <tt>Post#create_author!</tt> (similar to <tt>post.author = Author.new; post.author.save!; post.author</tt>) # The declaration can also include an +options+ hash to specialize the behavior of the association. # + # === Scopes + # + # You can pass a second argument +scope+ as a callable (i.e. proc or + # lambda) to retrieve a specific record or customize the generated query + # when you access the associated object. + # + # Scope examples: + # belongs_to :user, -> { where(id: 2) } + # belongs_to :user, -> { joins(:friends) } + # belongs_to :level, ->(level) { where("game_level > ?", level.current) } + # # === Options # # [:class_name] @@ -1543,6 +1578,18 @@ module ActiveRecord # * <tt>Developer#projects.create</tt> (similar to <tt>c = Project.new("developer_id" => id); c.save; c</tt>) # The declaration may include an +options+ hash to specialize the behavior of the association. # + # === Scopes + # + # You can pass a second argument +scope+ as a callable (i.e. proc or + # lambda) to retrieve a specific set of records or customize the generated + # query when you access the associated collection. + # + # Scope examples: + # has_and_belongs_to_many :projects, -> { includes :milestones, :manager } + # has_and_belongs_to_many :categories, ->(category) { + # where("default_category = ?", category.name) + # } + # # === Options # # [:class_name] |