+++ /dev/null
-module ActiveRecord
- # See ActiveRecord::AssociationPreload::ClassMethods for documentation.
- module AssociationPreload #:nodoc:
- def self.included(base)
- base.extend(ClassMethods)
- end
-
- # Implements the details of eager loading of ActiveRecord associations.
- # Application developers should not use this module directly.
- #
- # ActiveRecord::Base is extended with this module. The source code in
- # ActiveRecord::Base references methods defined in this module.
- #
- # Note that 'eager loading' and 'preloading' are actually the same thing.
- # However, there are two different eager loading strategies.
- #
- # The first one is by using table joins. This was only strategy available
- # prior to Rails 2.1. Suppose that you have an Author model with columns
- # 'name' and 'age', and a Book model with columns 'name' and 'sales'. Using
- # this strategy, ActiveRecord would try to retrieve all data for an author
- # and all of its books via a single query:
- #
- # SELECT * FROM authors
- # LEFT OUTER JOIN books ON authors.id = books.id
- # WHERE authors.name = 'Ken Akamatsu'
- #
- # However, this could result in many rows that contain redundant data. After
- # having received the first row, we already have enough data to instantiate
- # the Author object. In all subsequent rows, only the data for the joined
- # 'books' table is useful; the joined 'authors' data is just redundant, and
- # processing this redundant data takes memory and CPU time. The problem
- # quickly becomes worse and worse as the level of eager loading increases
- # (i.e. if ActiveRecord is to eager load the associations' assocations as
- # well).
- #
- # The second strategy is to use multiple database queries, one for each
- # level of association. Since Rails 2.1, this is the default strategy. In
- # situations where a table join is necessary (e.g. when the +:conditions+
- # option references an association's column), it will fallback to the table
- # join strategy.
- #
- # See also ActiveRecord::Associations::ClassMethods, which explains eager
- # loading in a more high-level (application developer-friendly) manner.
- module ClassMethods
- protected
-
- # Eager loads the named associations for the given ActiveRecord record(s).
- #
- # In this description, 'association name' shall refer to the name passed
- # to an association creation method. For example, a model that specifies
- # <tt>belongs_to :author</tt>, <tt>has_many :buyers</tt> has association
- # names +:author+ and +:buyers+.
- #
- # == Parameters
- # +records+ is an array of ActiveRecord::Base. This array needs not be flat,
- # i.e. +records+ itself may also contain arrays of records. In any case,
- # +preload_associations+ will preload the associations all records by
- # flattening +records+.
- #
- # +associations+ specifies one or more associations that you want to
- # preload. It may be:
- # - a Symbol or a String which specifies a single association name. For
- # example, specifiying +:books+ allows this method to preload all books
- # for an Author.
- # - an Array which specifies multiple association names. This array
- # is processed recursively. For example, specifying <tt>[:avatar, :books]</tt>
- # allows this method to preload an author's avatar as well as all of his
- # books.
- # - a Hash which specifies multiple association names, as well as
- # association names for the to-be-preloaded association objects. For
- # example, specifying <tt>{ :author => :avatar }</tt> will preload a
- # book's author, as well as that author's avatar.
- #
- # +:associations+ has the same format as the +:include+ option for
- # <tt>ActiveRecord::Base.find</tt>. So +associations+ could look like this:
- #
- # :books
- # [ :books, :author ]
- # { :author => :avatar }
- # [ :books, { :author => :avatar } ]
- #
- # +preload_options+ contains options that will be passed to ActiveRecord#find
- # (which is called under the hood for preloading records). But it is passed
- # only one level deep in the +associations+ argument, i.e. it's not passed
- # to the child associations when +associations+ is a Hash.
- def preload_associations(records, associations, preload_options={})
- records = [records].flatten.compact.uniq
- return if records.empty?
- case associations
- when Array then associations.each {|association| preload_associations(records, association, preload_options)}
- when Symbol, String then preload_one_association(records, associations.to_sym, preload_options)
- when Hash then
- associations.each do |parent, child|
- raise "parent must be an association name" unless parent.is_a?(String) || parent.is_a?(Symbol)
- preload_associations(records, parent, preload_options)
- reflection = reflections[parent]
- parents = records.map {|record| record.send(reflection.name)}.flatten.compact
- unless parents.empty?
- parents.first.class.preload_associations(parents, child)
- end
- end
- end
- end
-
- private
-
- # Preloads a specific named association for the given records. This is
- # called by +preload_associations+ as its base case.
- def preload_one_association(records, association, preload_options={})
- class_to_reflection = {}
- # Not all records have the same class, so group then preload
- # group on the reflection itself so that if various subclass share the same association then we do not split them
- # unnecessarily
- records.group_by {|record| class_to_reflection[record.class] ||= record.class.reflections[association]}.each do |reflection, records|
- raise ConfigurationError, "Association named '#{ association }' was not found; perhaps you misspelled it?" unless reflection
-
- # 'reflection.macro' can return 'belongs_to', 'has_many', etc. Thus,
- # the following could call 'preload_belongs_to_association',
- # 'preload_has_many_association', etc.
- send("preload_#{reflection.macro}_association", records, reflection, preload_options)
- end
- end
-
- def add_preloaded_records_to_collection(parent_records, reflection_name, associated_record)
- parent_records.each do |parent_record|
- association_proxy = parent_record.send(reflection_name)
- association_proxy.loaded
- association_proxy.target.push(*[associated_record].flatten)
- end
- end
-
- def add_preloaded_record_to_collection(parent_records, reflection_name, associated_record)
- parent_records.each do |parent_record|
- parent_record.send("set_#{reflection_name}_target", associated_record)
- end
- end
-
- def set_association_collection_records(id_to_record_map, reflection_name, associated_records, key)
- associated_records.each do |associated_record|
- mapped_records = id_to_record_map[associated_record[key].to_s]
- add_preloaded_records_to_collection(mapped_records, reflection_name, associated_record)
- end
- end
-
- def set_association_single_records(id_to_record_map, reflection_name, associated_records, key)
- seen_keys = {}
- associated_records.each do |associated_record|
- #this is a has_one or belongs_to: there should only be one record.
- #Unfortunately we can't (in portable way) ask the database for 'all records where foo_id in (x,y,z), but please
- # only one row per distinct foo_id' so this where we enforce that
- next if seen_keys[associated_record[key].to_s]
- seen_keys[associated_record[key].to_s] = true
- mapped_records = id_to_record_map[associated_record[key].to_s]
- mapped_records.each do |mapped_record|
- mapped_record.send("set_#{reflection_name}_target", associated_record)
- end
- end
- end
-
- # Given a collection of ActiveRecord objects, constructs a Hash which maps
- # the objects' IDs to the relevant objects. Returns a 2-tuple
- # <tt>(id_to_record_map, ids)</tt> where +id_to_record_map+ is the Hash,
- # and +ids+ is an Array of record IDs.
- def construct_id_map(records, primary_key=nil)
- id_to_record_map = {}
- ids = []
- records.each do |record|
- primary_key ||= record.class.primary_key
- ids << record[primary_key]
- mapped_records = (id_to_record_map[ids.last.to_s] ||= [])
- mapped_records << record
- end
- ids.uniq!
- return id_to_record_map, ids
- end
-
- def preload_has_and_belongs_to_many_association(records, reflection, preload_options={})
- table_name = reflection.klass.quoted_table_name
- id_to_record_map, ids = construct_id_map(records)
- records.each {|record| record.send(reflection.name).loaded}
- options = reflection.options
-
- conditions = "t0.#{reflection.primary_key_name} #{in_or_equals_for_ids(ids)}"
- conditions << append_conditions(reflection, preload_options)
-
- associated_records = reflection.klass.with_exclusive_scope do
- reflection.klass.find(:all, :conditions => [conditions, ids],
- :include => options[:include],
- :joins => "INNER JOIN #{connection.quote_table_name options[:join_table]} t0 ON #{reflection.klass.quoted_table_name}.#{reflection.klass.primary_key} = t0.#{reflection.association_foreign_key}",
- :select => "#{options[:select] || table_name+'.*'}, t0.#{reflection.primary_key_name} as the_parent_record_id",
- :order => options[:order])
- end
- set_association_collection_records(id_to_record_map, reflection.name, associated_records, 'the_parent_record_id')
- end
-
- def preload_has_one_association(records, reflection, preload_options={})
- return if records.first.send("loaded_#{reflection.name}?")
- id_to_record_map, ids = construct_id_map(records, reflection.options[:primary_key])
- options = reflection.options
- records.each {|record| record.send("set_#{reflection.name}_target", nil)}
- if options[:through]
- through_records = preload_through_records(records, reflection, options[:through])
- through_reflection = reflections[options[:through]]
- through_primary_key = through_reflection.primary_key_name
- unless through_records.empty?
- source = reflection.source_reflection.name
- through_records.first.class.preload_associations(through_records, source)
- if through_reflection.macro == :belongs_to
- rev_id_to_record_map, rev_ids = construct_id_map(records, through_primary_key)
- rev_primary_key = through_reflection.klass.primary_key
- through_records.each do |through_record|
- add_preloaded_record_to_collection(rev_id_to_record_map[through_record[rev_primary_key].to_s],
- reflection.name, through_record.send(source))
- end
- else
- through_records.each do |through_record|
- add_preloaded_record_to_collection(id_to_record_map[through_record[through_primary_key].to_s],
- reflection.name, through_record.send(source))
- end
- end
- end
- else
- set_association_single_records(id_to_record_map, reflection.name, find_associated_records(ids, reflection, preload_options), reflection.primary_key_name)
- end
- end
-
- def preload_has_many_association(records, reflection, preload_options={})
- return if records.first.send(reflection.name).loaded?
- options = reflection.options
-
- primary_key_name = reflection.through_reflection_primary_key_name
- id_to_record_map, ids = construct_id_map(records, primary_key_name || reflection.options[:primary_key])
- records.each {|record| record.send(reflection.name).loaded}
-
- if options[:through]
- through_records = preload_through_records(records, reflection, options[:through])
- through_reflection = reflections[options[:through]]
- unless through_records.empty?
- source = reflection.source_reflection.name
- through_records.first.class.preload_associations(through_records, source, options)
- through_records.each do |through_record|
- through_record_id = through_record[reflection.through_reflection_primary_key].to_s
- add_preloaded_records_to_collection(id_to_record_map[through_record_id], reflection.name, through_record.send(source))
- end
- end
-
- else
- set_association_collection_records(id_to_record_map, reflection.name, find_associated_records(ids, reflection, preload_options),
- reflection.primary_key_name)
- end
- end
-
- def preload_through_records(records, reflection, through_association)
- through_reflection = reflections[through_association]
- through_primary_key = through_reflection.primary_key_name
-
- if reflection.options[:source_type]
- interface = reflection.source_reflection.options[:foreign_type]
- preload_options = {:conditions => ["#{connection.quote_column_name interface} = ?", reflection.options[:source_type]]}
-
- records.compact!
- records.first.class.preload_associations(records, through_association, preload_options)
-
- # Dont cache the association - we would only be caching a subset
- through_records = []
- records.each do |record|
- proxy = record.send(through_association)
-
- if proxy.respond_to?(:target)
- through_records << proxy.target
- proxy.reset
- else # this is a has_one :through reflection
- through_records << proxy if proxy
- end
- end
- through_records.flatten!
- else
- records.first.class.preload_associations(records, through_association)
- through_records = records.map {|record| record.send(through_association)}.flatten
- end
- through_records.compact!
- through_records
- end
-
- def preload_belongs_to_association(records, reflection, preload_options={})
- return if records.first.send("loaded_#{reflection.name}?")
- options = reflection.options
- primary_key_name = reflection.primary_key_name
-
- if options[:polymorphic]
- polymorph_type = options[:foreign_type]
- klasses_and_ids = {}
-
- # Construct a mapping from klass to a list of ids to load and a mapping of those ids back to their parent_records
- records.each do |record|
- if klass = record.send(polymorph_type)
- klass_id = record.send(primary_key_name)
- if klass_id
- id_map = klasses_and_ids[klass] ||= {}
- id_list_for_klass_id = (id_map[klass_id.to_s] ||= [])
- id_list_for_klass_id << record
- end
- end
- end
- klasses_and_ids = klasses_and_ids.to_a
- else
- id_map = {}
- records.each do |record|
- key = record.send(primary_key_name)
- if key
- mapped_records = (id_map[key.to_s] ||= [])
- mapped_records << record
- end
- end
- klasses_and_ids = [[reflection.klass.name, id_map]]
- end
-
- klasses_and_ids.each do |klass_and_id|
- klass_name, id_map = *klass_and_id
- next if id_map.empty?
- klass = klass_name.constantize
-
- table_name = klass.quoted_table_name
- primary_key = klass.primary_key
- column_type = klass.columns.detect{|c| c.name == primary_key}.type
- ids = id_map.keys.map do |id|
- if column_type == :integer
- id.to_i
- elsif column_type == :float
- id.to_f
- else
- id
- end
- end
- conditions = "#{table_name}.#{connection.quote_column_name(primary_key)} #{in_or_equals_for_ids(ids)}"
- conditions << append_conditions(reflection, preload_options)
- associated_records = klass.with_exclusive_scope do
- klass.find(:all, :conditions => [conditions, ids],
- :include => options[:include],
- :select => options[:select],
- :joins => options[:joins],
- :order => options[:order])
- end
- set_association_single_records(id_map, reflection.name, associated_records, primary_key)
- end
- end
-
- def find_associated_records(ids, reflection, preload_options)
- options = reflection.options
- table_name = reflection.klass.quoted_table_name
-
- if interface = reflection.options[:as]
- conditions = "#{reflection.klass.quoted_table_name}.#{connection.quote_column_name "#{interface}_id"} #{in_or_equals_for_ids(ids)} and #{reflection.klass.quoted_table_name}.#{connection.quote_column_name "#{interface}_type"} = '#{self.base_class.sti_name}'"
- else
- foreign_key = reflection.primary_key_name
- conditions = "#{reflection.klass.quoted_table_name}.#{foreign_key} #{in_or_equals_for_ids(ids)}"
- end
-
- conditions << append_conditions(reflection, preload_options)
-
- reflection.klass.with_exclusive_scope do
- reflection.klass.find(:all,
- :select => (preload_options[:select] || options[:select] || "#{table_name}.*"),
- :include => preload_options[:include] || options[:include],
- :conditions => [conditions, ids],
- :joins => options[:joins],
- :group => preload_options[:group] || options[:group],
- :order => preload_options[:order] || options[:order])
- end
- end
-
-
- def interpolate_sql_for_preload(sql)
- instance_eval("%@#{sql.gsub('@', '\@')}@")
- end
-
- def append_conditions(reflection, preload_options)
- sql = ""
- sql << " AND (#{interpolate_sql_for_preload(reflection.sanitized_conditions)})" if reflection.sanitized_conditions
- sql << " AND (#{sanitize_sql preload_options[:conditions]})" if preload_options[:conditions]
- sql
- end
-
- def in_or_equals_for_ids(ids)
- ids.size > 1 ? "IN (?)" : "= ?"
- end
- end
- end
-end
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