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Fuse traversals of the record set when preloading

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Although consuming code will almost certainly retraverse this set, we can avoid
walking it twice here. As an extra upside, we can avoid the double-use of an
identity-sensitive hash; this is convenient, because it is another collection we
actually don't need to build.
This commit is contained in:
Michael Fowler 2019-12-29 18:24:34 +13:00
parent 9aa59f9d4a
commit 989dda36d6
1 changed files with 27 additions and 25 deletions
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52
activerecord/lib/active_record/associations/preloader/association.rb
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@ -27,40 +27,42 @@ module ActiveRecord
end
def records_by_owner
# owners can be duplicated when a relation has a collection association join
# #compare_by_identity makes such owners different hash keys
@records_by_owner ||= preloaded_records.each_with_object({}.compare_by_identity) do |record, result|
owners_by_key[convert_key(record[association_key_name])].each do |owner|
(result[owner] ||= []) << record
end
end
load_records unless defined?(@records_by_owner)
@records_by_owner
end
def preloaded_records
return @preloaded_records if defined?(@preloaded_records)
load_records unless defined?(@preloaded_records)
raw_records = owner_keys.empty? ? [] : records_for(owner_keys)
seen_records_by_owner = {}.compare_by_identity
@preloaded_records = raw_records.select do |record|
assignments = []
owners_by_key[convert_key(record[association_key_name])].each do |owner|
entries = (seen_records_by_owner[owner] ||= [])
if reflection.collection? || entries.empty?
entries << record
assignments << record
end
end
!assignments.empty?
end
@preloaded_records
end
private
attr_reader :owners, :reflection, :preload_scope, :model, :klass
def load_records
# owners can be duplicated when a relation has a collection association join
# #compare_by_identity makes such owners different hash keys
@records_by_owner = {}.compare_by_identity
raw_records = owner_keys.empty? ? [] : records_for(owner_keys)
@preloaded_records = raw_records.select do |record|
assignments = []
owners_by_key[convert_key(record[association_key_name])].each do |owner|
entries = (@records_by_owner[owner] ||= [])
if reflection.collection? || entries.empty?
entries << record
assignments << record
end
end
!assignments.empty?
end
end
# The name of the key on the associated records
def association_key_name
reflection.join_primary_key(klass)