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module ActiveRecord
module Associations
class Preloader
class HasAndBelongsToMany < CollectionAssociation #:nodoc:
attr_reader :join_table
def initialize(klass, records, reflection, preload_options)
super
@join_table = Arel::Table.new(reflection.join_table).alias('t0')
end
# Unlike the other associations, we want to get a raw array of rows so that we can
# access the aliased column on the join table
def records_for(ids)
scope = query_scope ids
klass.connection.select_all(scope.arel, 'SQL', scope.bind_values)
end
def owner_key_name
reflection.active_record_primary_key
end
def association_key_name
'ar_association_key_name'
end
def association_key
join_table[reflection.foreign_key]
end
private
# Once we have used the join table column (in super), we manually instantiate the
# actual records, ensuring that we don't create more than one instances of the same
# record
def load_slices(slices)
identity_map = {}
caster = nil
name = association_key_name
records_to_keys = slices.flat_map { |slice|
records = records_for(slice)
caster ||= records.column_types.fetch(name, records.identity_type)
records.map! { |row|
record = identity_map[row[klass.primary_key]] ||= klass.instantiate(row)
[record, caster.type_cast(row[name])]
}
}
@preloaded_records = records_to_keys.map(&:first)
records_to_keys
end
def build_scope
super.joins(join).select(join_select)
end
def join_select
association_key.as(Arel.sql(association_key_name))
end
def join
condition = table[reflection.association_primary_key].eq(
join_table[reflection.association_foreign_key])
table.create_join(join_table, table.create_on(condition))
end
end
end
end
end
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