require 'active_support/core_ext/array/wrap' require 'active_support/core_ext/enumerable' module ActiveRecord # See ActiveRecord::AssociationPreload::ClassMethods for documentation. module AssociationPreload #:nodoc: extend ActiveSupport::Concern # Implements the details of eager loading of Active Record 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, Active Record 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 Active Record is to eager load the associations' associations 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 Active Record record(s). # # In this description, 'association name' shall refer to the name passed # to an association creation method. For example, a model that specifies # belongs_to :author, has_many :buyers 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 all associations 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, specifying +: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 [:avatar, :books] # 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 { :author => :avatar } will preload a # book's author, as well as that author's avatar. # # +:associations+ has the same format as the +:include+ option for # ActiveRecord::Base.find. So +associations+ could look like this: # # :books # [ :books, :author ] # { :author => :avatar } # [ :books, { :author => :avatar } ] # # +preload_options+ contains options that will be passed to ActiveRecord::Base#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 = Array.wrap(records).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.sum { |record| Array.wrap(record.send(reflection.name)) } 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(*Array.wrap(associated_record)) association_proxy.__send__(:set_inverse_instance, associated_record, parent_record) 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| association_proxy = mapped_record.send("set_#{reflection_name}_target", associated_record) association_proxy.__send__(:set_inverse_instance, associated_record, mapped_record) end end id_to_record_map.each do |id, records| next if seen_keys.include?(id.to_s) records.each {|record| record.send("set_#{reflection_name}_target", nil) } end end # Given a collection of Active Record objects, constructs a Hash which maps # the objects' IDs to the relevant objects. Returns a 2-tuple # (id_to_record_map, ids) 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.unscoped.where([conditions, ids]). includes(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]).to_a set_association_collection_records(id_to_record_map, reflection.name, associated_records, 'the_parent_record_id') end def preload_has_one_or_has_many_association(records, reflection, preload_options={}) if reflection.macro == :has_many return if records.first.send(reflection.name).loaded? records.each { |record| record.send(reflection.name).loaded } else return if records.first.send("loaded_#{reflection.name}?") records.each {|record| record.send("set_#{reflection.name}_target", nil)} end options = reflection.options if options[:through] records_with_through_records = preload_through_records(records, reflection, options[:through]) all_through_records = records_with_through_records.map(&:last).flatten unless all_through_records.empty? source = reflection.source_reflection.name all_through_records.first.class.preload_associations(all_through_records, source, options) records_with_through_records.each do |record, through_records| source_records = through_records.map(&source).flatten.compact case reflection.macro when :has_many, :has_and_belongs_to_many add_preloaded_records_to_collection([record], reflection.name, source_records) when :has_one, :belongs_to add_preloaded_record_to_collection([record], reflection.name, source_records.first) end end end else id_to_record_map, ids = construct_id_map(records, reflection.options[:primary_key]) associated_records = find_associated_records(ids, reflection, preload_options) if reflection.macro == :has_many set_association_collection_records( id_to_record_map, reflection.name, associated_records, reflection.primary_key_name ) else set_association_single_records( id_to_record_map, reflection.name, associated_records, reflection.primary_key_name ) end end end alias_method :preload_has_one_association, :preload_has_one_or_has_many_association alias_method :preload_has_many_association, :preload_has_one_or_has_many_association def preload_through_records(records, reflection, through_association) through_reflection = reflections[through_association] # If the same through record is loaded twice, we want to return exactly the same # object in the result, rather than two separate instances representing the same # record. This is so that we can preload the source association for each record, # and always be able to access the preloaded association regardless of where we # refer to the record. # # Suffices to say, if AR had an identity map built in then this would be unnecessary. identity_map = {} options = {} if reflection.options[:source_type] interface = reflection.source_reflection.options[:foreign_type] options[:conditions] = ["#{connection.quote_column_name interface} = ?", reflection.options[:source_type]] records.compact! else if reflection.options[:conditions] options[:include] = reflection.options[:include] || reflection.options[:source] options[:conditions] = reflection.options[:conditions] end options[:order] = reflection.options[:order] end records.first.class.preload_associations(records, through_association, options) records.map do |record| if reflection.options[:source_type] # Dont cache the association - we would only be caching a subset 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 end else through_records = record.send(through_association) end through_records = Array.wrap(through_records).map do |through_record| identity_map[through_record] ||= through_record end [record, through_records] end 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 klasses_and_ids = {} if options[:polymorphic] polymorph_type = options[:foreign_type] # 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_map[klass_id.to_s] ||= []) << record end end end else id_map = {} records.each do |record| key = record.send(primary_key_name) (id_map[key.to_s] ||= []) << record if key end klasses_and_ids[reflection.klass.name] = id_map unless id_map.empty? end klasses_and_ids.each do |klass_name, _id_map| klass = klass_name.constantize table_name = klass.quoted_table_name primary_key = reflection.options[: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.unscoped.where([conditions, ids]).apply_finder_options(options.slice(:include, :select, :joins, :order)).to_a 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) find_options = { :select => preload_options[:select] || options[:select] || Arel::SqlLiteral.new("#{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] } reflection.klass.scoped.apply_finder_options(find_options).to_a end def interpolate_sql_for_preload(sql) instance_eval("%@#{sql.gsub('@', '\@')}@", __FILE__, __LINE__) 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