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