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When preloading has_and_belongs_to_many associations, we should only …

…instantiate one AR object per actual record in the database. (Even when IM is off.)
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1 parent af27262 commit 8987cda2bb64fe289f7a28b2833a2786cfbc8259 @jonleighton jonleighton committed with tenderlove Mar 4, 2011
@@ -31,10 +31,12 @@ def association_key
private
# Once we have used the join table column (in super), we manually instantiate the
- # actual records
+ # actual records, ensuring that we don't create more than one instances of the same
+ # record
def associated_records_by_owner
+ records = {}
super.each do |owner_key, rows|
- rows.map! { |row| klass.instantiate(row) }
+ rows.map! { |row| records[row[klass.primary_key]] ||= klass.instantiate(row) }
end
end
@@ -525,6 +525,22 @@ def test_eager_with_has_and_belongs_to_many_and_limit
assert posts[1].categories.include?(categories(:general))
end
+ # This is only really relevant when the identity map is off. Since the preloader for habtm
+ # gets raw row hashes from the database and then instantiates them, this test ensures that
+ # it only instantiates one actual object per record from the database.
+ def test_has_and_belongs_to_many_should_not_instantiate_same_records_multiple_times
+ welcome = posts(:welcome)
+ categories = Category.includes(:posts)
+
+ general = categories.find { |c| c == categories(:general) }
+ technology = categories.find { |c| c == categories(:technology) }
+
+ post1 = general.posts.to_a.find { |p| p == posts(:welcome) }
+ post2 = technology.posts.to_a.find { |p| p == posts(:welcome) }
+
+ assert_equal post1.object_id, post2.object_id
+ end
+
def test_eager_with_has_many_and_limit_and_conditions_on_the_eagers
posts = authors(:david).posts.find(:all,
:include => :comments,

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