fix for not saving related model in reverse rel

tests/test_queries/test_adding_related.py

@@ -0,0 +1,54 @@
+from typing import Optional
+
+import databases
+import pytest
+import sqlalchemy
+import asyncio
+
+import ormar
+
+from tests.settings import DATABASE_URL
+
+database = databases.Database(DATABASE_URL)
+metadata = sqlalchemy.MetaData()
+
+
+class Department(ormar.Model):
+    class Meta:
+        database = database
+        metadata = metadata
+
+    id: int = ormar.Integer(primary_key=True)
+    name: str = ormar.String(max_length=100)
+
+
+class Course(ormar.Model):
+    class Meta:
+        database = database
+        metadata = metadata
+
+    id: int = ormar.Integer(primary_key=True)
+    name: str = ormar.String(max_length=100)
+    completed: bool = ormar.Boolean(default=False)
+    department: Optional[Department] = ormar.ForeignKey(Department)
+
+
+@pytest.fixture(autouse=True, scope="module")
+def create_test_database():
+    engine = sqlalchemy.create_engine(DATABASE_URL)
+    metadata.drop_all(engine)
+    metadata.create_all(engine)
+    yield
+    metadata.drop_all(engine)
+
+
+@pytest.mark.asyncio
+async def test_adding_relation_to_reverse_saves_the_child():
+    async with database:
+        department = await Department(name="Science").save()
+        course = Course(name="Math", completed=False)
+
+        await department.courses.add(course)
+        assert course.pk is not None
+        assert course.department == department
+        assert department.courses[0] == course