add tests for mysql and postgress, some fixes for those backends

tests/test_same_table_joins.py

@@ -78,6 +78,11 @@ async def create_test_database():
     engine = sqlalchemy.create_engine(DATABASE_URL)
     metadata.drop_all(engine)
     metadata.create_all(engine)
+    yield
+    metadata.drop_all(engine)
+
+
+async def create_data():
     department = await Department.objects.create(id=1, name="Math Department")
     department2 = await Department.objects.create(id=2, name="Law Department")
     class1 = await SchoolClass.objects.create(name="Math", department=department)
@@ -88,52 +93,56 @@ async def create_test_database():
     await Student.objects.create(name="Judy", category=category2, schoolclass=class1)
     await Student.objects.create(name="Jack", category=category2, schoolclass=class2)
     await Teacher.objects.create(name="Joe", category=category2, schoolclass=class1)
-    yield
-    metadata.drop_all(engine)
 
 
 @pytest.mark.asyncio
 async def test_model_multiple_instances_of_same_table_in_schema():
     async with database:
-        classes = await SchoolClass.objects.select_related(
-            ["teachers__category", "students"]
-        ).all()
-        assert classes[0].name == "Math"
-        assert classes[0].students[0].name == "Jane"
+        async with database.transaction(force_rollback=True):
+            await create_data()
+            classes = await SchoolClass.objects.select_related(
+                ["teachers__category", "students"]
+            ).all()
+            assert classes[0].name == "Math"
+            assert classes[0].students[0].name == "Jane"
 
-        assert len(classes[0].dict().get("students")) == 2
+            assert len(classes[0].dict().get("students")) == 2
 
-        # since it's going from schoolclass => teacher => schoolclass (same class) department is already populated
-        assert classes[0].students[0].schoolclass.name == "Math"
-        assert classes[0].students[0].schoolclass.department.name is None
-        await classes[0].students[0].schoolclass.department.load()
-        assert classes[0].students[0].schoolclass.department.name == "Math Department"
+            # since it's going from schoolclass => teacher => schoolclass (same class) department is already populated
+            assert classes[0].students[0].schoolclass.name == "Math"
+            assert classes[0].students[0].schoolclass.department.name is None
+            await classes[0].students[0].schoolclass.department.load()
+            assert classes[0].students[0].schoolclass.department.name == "Math Department"
 
-        await classes[1].students[0].schoolclass.department.load()
-        assert classes[1].students[0].schoolclass.department.name == "Law Department"
+            await classes[1].students[0].schoolclass.department.load()
+            assert classes[1].students[0].schoolclass.department.name == "Law Department"
 
 
 @pytest.mark.asyncio
 async def test_right_tables_join():
     async with database:
-        classes = await SchoolClass.objects.select_related(
-            ["teachers__category", "students"]
-        ).all()
-        assert classes[0].teachers[0].category.name == "Domestic"
+        async with database.transaction(force_rollback=True):
+            await create_data()
+            classes = await SchoolClass.objects.select_related(
+                ["teachers__category", "students"]
+            ).all()
+            assert classes[0].teachers[0].category.name == "Domestic"
 
-        assert classes[0].students[0].category.name is None
-        await classes[0].students[0].category.load()
-        assert classes[0].students[0].category.name == "Foreign"
+            assert classes[0].students[0].category.name is None
+            await classes[0].students[0].category.load()
+            assert classes[0].students[0].category.name == "Foreign"
 
 
 @pytest.mark.asyncio
 async def test_multiple_reverse_related_objects():
     async with database:
-        classes = await SchoolClass.objects.select_related(
-            ["teachers__category", "students__category"]
-        ).all()
-        assert classes[0].name == "Math"
-        assert classes[0].students[1].name == "Judy"
-        assert classes[0].students[0].category.name == "Foreign"
-        assert classes[0].students[1].category.name == "Domestic"
-        assert classes[0].teachers[0].category.name == "Domestic"
+        async with database.transaction(force_rollback=True):
+            await create_data()
+            classes = await SchoolClass.objects.select_related(
+                ["teachers__category", "students__category"]
+            ).all()
+            assert classes[0].name == "Math"
+            assert classes[0].students[1].name == "Judy"
+            assert classes[0].students[0].category.name == "Foreign"
+            assert classes[0].students[1].category.name == "Domestic"
+            assert classes[0].teachers[0].category.name == "Domestic"