feat: post delete and post save usercourse instances (#325)

* feat: post delete and post save usercourse

- Change user`s last course viewed depending on the saving and deleting of usercourses instances
- Added a test
- Added a constraint

Author: orronai

Diff for: lms/lmsdb/bootstrap.py

@@ -287,6 +287,15 @@ def _add_exercise_course_id_and_number_columns_constraint() -> bool:
         db_config.database.commit()
 
 
+def _add_user_course_constaint() -> bool:
+    migrator = db_config.get_migrator_instance()
+    with db_config.database.transaction():
+        migrate(
+            migrator.add_index('usercourse', ('user_id', 'course_id'), True),
+        )
+        db_config.database.commit()
+
+
 def _last_status_view_migration() -> bool:
     Solution = models.Solution
     _migrate_column_in_table_if_needed(Solution, Solution.last_status_view)
@@ -312,6 +321,9 @@ def main():
             _last_course_viewed_migration()
             _uuid_migration()
 
+        if models.database.table_exists(models.UserCourse.__name__.lower()):
+            _add_user_course_constaint()
+
         models.database.create_tables(models.ALL_MODELS, safe=True)
 
         if models.Role.select().count() == 0:

Diff for: lms/lmsdb/models.py

@@ -16,7 +16,9 @@
     BooleanField, Case, CharField, Check, DateTimeField, ForeignKeyField,
     IntegerField, JOIN, ManyToManyField, TextField, UUIDField, fn,
 )
-from playhouse.signals import Model, post_save, pre_save  # type: ignore
+from playhouse.signals import (  # type: ignore
+    Model, post_delete, post_save, pre_save,
+)
 from werkzeug.security import (
     check_password_hash, generate_password_hash,
 )
@@ -252,6 +254,11 @@ class UserCourse(BaseModel):
     course = ForeignKeyField(Course, backref='usercourses')
     date = DateTimeField(default=datetime.now)
 
+    class Meta:
+        indexes = (
+            (('user_id', 'course_id'), True),
+        )
+
     @classmethod
     def is_user_registered(cls, user_id: int, course_id: int) -> bool:
         return (
@@ -265,6 +272,24 @@ def is_user_registered(cls, user_id: int, course_id: int) -> bool:
         )
 
 
+@post_save(sender=UserCourse)
+def on_save_user_course(model_class, instance, created):
+    """Changes user's last course viewed."""
+    if instance.user.last_course_viewed is None:
+        instance.user.last_course_viewed = instance.course
+        instance.user.save()
+
+
+@post_delete(sender=UserCourse)
+def on_delete_user_course(model_class, instance):
+    """Changes user's last course viewed."""
+    if instance.user.last_course_viewed == instance.course:
+        instance.user.last_course_viewed = (
+            Course.fetch(instance.user).limit(1).scalar()
+        )
+        instance.user.save()
+
+
 class Notification(BaseModel):
     ID_FIELD_NAME = 'id'
     MAX_PER_USER = 10

Diff for: tests/test_users.py

@@ -185,3 +185,22 @@ def test_user_registered_to_course(student_user: User, course: Course):
         course2 = conftest.create_course(index=1)
         assert not course2.has_user(student_user)
 
+    @staticmethod
+    def test_usercourse_on_delete(student_user: User, course: Course):
+        usercourse = conftest.create_usercourse(student_user, course)
+        assert student_user.last_course_viewed == course
+
+        usercourse.delete_instance()
+        assert student_user.last_course_viewed is None
+
+    @staticmethod
+    def test_usercourse_on_save(student_user: User, course: Course):
+        course2 = conftest.create_course(index=1)
+        usercourse = conftest.create_usercourse(student_user, course)
+        assert student_user.last_course_viewed == course
+
+        conftest.create_usercourse(student_user, course2)
+        assert student_user.last_course_viewed == course
+
+        usercourse.delete_instance()
+        assert student_user.last_course_viewed == course2