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 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' 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 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, 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 <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 = 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
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
through_records = []
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
records.each do |record|
proxy = record.send(through_association)
if proxy.respond_to?(:target)
through_records.concat Array.wrap(proxy.target)
proxy.reset
else # this is a has_one :through reflection
through_records << proxy if proxy
end
end
else
records.first.class.preload_associations(records, through_association)
records.each do |record|
through_records.concat Array.wrap(record.send(through_association))
end
end
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
