Cannot filter by composite foreign key

I would expect to be able to filter on a child related to a parent on the child's composite foreign key to the parent (the same way that I can access the foreign key using the generated accessor). The following test case might explain better what I mean:

diff --git a/persistent-test/CompositeTest.hs b/persistent-test/CompositeTest.hs
index b3829b9..b2d54c9 100644
--- a/persistent-test/CompositeTest.hs
+++ b/persistent-test/CompositeTest.hs
@@ -179,6 +179,16 @@ specs = describe "composite" $
       c1 @== c11
       testChildFkparent c11 @== kp1

+    it "Filter by Foreign Key from Child value" $ db $ do
+      kp1 <- insert p1
+      _ <- insert p2
+      kc1 <- insert c1
+      xs <- selectList [TestChildFkparent ==. kp1] []
+      length xs @== 1
+      let [Entity newkc1 newc1] = xs 
+      c1 @== newc1
+      kc1 @== newkc1
+
 #ifndef WITH_MYSQL
     it "Tree relationships" $ db $ do
       kgp@(TreeKey gpt) <- insert $ Tree "grandpa" Nothing

However, the TestChildFkparent constructor is not generated by Peristent's TH (while the testChildFkparent accessor is). This would be very useful for generating join conditions using Esqueleto. This is related to https://github.com/prowdsponsor/esqueleto/pull/87 and https://github.com/prowdsponsor/esqueleto/pull/88

Start with the proposed regression test in persistent-test/CompositeTest.hs and inspect how Persistent's TH generates the testChildFkparent accessor. Trace the related composite foreign-key generation and Esqueleto references from the linked issues. Done means the TestChildFkparent constructor is generated and the filtering test passes.