feat: add mapper for student and it loads

tests/integration/test_orm.py

@@ -1,4 +1,5 @@
 from backend.adapters.orm import metadata, start_mappers
+from backend.model.student import Student
 from backend.model.tribe import Tribe
 
 
@@ -40,3 +41,25 @@ def test_tribe_mapper_can_save_and_load_tribe(session):
     session.commit()
 
     assert session.query(Tribe).all() == [tribe]
+
+
+def test_students_mapper_can_load_student(session):
+    session.execute("INSERT INTO tribes (name, level) VALUES " "('tribe1', '2nd')")
+
+    session.execute(
+        "INSERT INTO students (id, name, tribe_name) VALUES "
+        "('1', 'student1', 'tribe1'),"
+        "('2', 'student2', 'tribe1')"
+    )
+
+    tribe = session.query(Tribe).one()
+    expected = [
+        (Student("1", "student1", tribe)),
+        (Student("2", "student2", tribe)),
+    ]
+
+    with session.no_autoflush:
+        students = session.query(Student).all()
+
+    assert set(tribe.students) == set(expected)
+    assert students == expected