Cope with foreign keys which are primary keys

This removes the assumption that all models have a field called
'id' and ensures that we use the correct column name for each field.

Fixes #40.

Author: PeterJCLaw

psqlextra/compiler.py

@@ -155,12 +155,13 @@ def _rewrite_insert_nothing(self, sql, params, returning):
             (
                 'WITH insdata AS ('
                 '{insert} ON CONFLICT {conflict_target} DO UPDATE'
-                ' SET id = NULL WHERE FALSE RETURNING {returning})'
+                ' SET {pk_column} = NULL WHERE FALSE RETURNING {returning})'
                 ' SELECT * FROM insdata UNION ALL'
                 ' SELECT {returning} FROM {table} WHERE {where_clause} LIMIT 1;'
             ).format(
                 insert=sql,
                 conflict_target=conflict_target,
+                pk_column=self.qn(self.query.model._meta.pk.column),
                 returning=returning,
                 table=self.query.objs[0]._meta.db_table,
                 where_clause=where_clause

tests/test_on_conflict_nothing.py

@@ -39,3 +39,46 @@ def test_on_conflict_nothing():
     assert obj1.cookies == 'cheers'
     assert obj2.title['key1'] == 'beer'
     assert obj2.cookies == 'cheers'
+
+
+def test_on_conflict_nothing_foreign_primary_key():
+    """
+    Tests whether simple insert NOTHING works correctly when the primary key of
+    a field is a foreign key with a custom name.
+    """
+
+    referenced_model = get_fake_model({})
+
+    model = get_fake_model({
+        'parent': models.OneToOneField(
+            referenced_model,
+            primary_key=True,
+            on_delete=models.CASCADE,
+        ),
+        'cookies': models.CharField(max_length=255, null=True)
+    })
+
+    referenced_obj = referenced_model.objects.create()
+
+    obj1 = (
+        model.objects
+        .on_conflict(['parent'], ConflictAction.NOTHING)
+        .insert_and_get(parent=referenced_obj, cookies='cheers')
+    )
+
+    obj1.refresh_from_db()
+    assert obj1.parent == referenced_obj
+    assert obj1.cookies == 'cheers'
+
+    obj2 = (
+        model.objects
+        .on_conflict(['parent'], ConflictAction.NOTHING)
+        .insert_and_get(parent=referenced_obj, cookies='choco')
+    )
+
+    obj1.refresh_from_db()
+    obj2.refresh_from_db()
+
+    assert obj1.pk == obj2.pk
+    assert obj1.cookies == 'cheers'
+    assert obj2.cookies == 'cheers'