Referential Actions Enum Class (#735)

* feat: add action enum class to referential actions

* feat: write validation func for action name string

* test: write test for validation referential action

* fix: backend database running for action test

* fix: set the string type of value enum class

* fix: debuging return statement type for validation

* fix: return non empty for empty action

* refactor: change in line return if statement

* fix: add iterate method in read document md

* fix: update foreign key docstring types

* docs: write documention of refernal actions

* docs: complete referential actions descriptions

* refactor: rename and reposition referential action

* refactor: change validate referential action func

* test: add assert check for really deleted rows

* fix: debug error problem in renamed enum class

* fix: apply black formatted codes

* docs: update the document for referential actions

* docs: added note for server default argument

Co-authored-by: collerek <collerek@gmail.com>

tests/test_relations/test_database_fk_creation.py

@@ -5,6 +5,7 @@ import pytest
 import sqlalchemy
 
 import ormar
+from ormar.fields.foreign_key import validate_referential_action
 from tests.settings import DATABASE_URL
 
 database = databases.Database(DATABASE_URL)
@@ -33,6 +34,35 @@ class Album(ormar.Model):
     artist: Optional[Artist] = ormar.ForeignKey(Artist, ondelete="CASCADE")
 
 
+class A(ormar.Model):
+    class Meta:
+        metadata = metadata
+        database = database
+
+    id: int = ormar.Integer(primary_key=True)
+    name: str = ormar.String(max_length=64, nullalbe=False)
+
+
+class B(ormar.Model):
+    class Meta:
+        metadata = metadata
+        database = database
+
+    id: int = ormar.Integer(primary_key=True)
+    name: str = ormar.String(max_length=64, nullalbe=False)
+    a: A = ormar.ForeignKey(to=A, ondelete=ormar.ReferentialAction.CASCADE)
+
+
+class C(ormar.Model):
+    class Meta:
+        metadata = metadata
+        database = database
+
+    id: int = ormar.Integer(primary_key=True)
+    name: str = ormar.String(max_length=64, nullalbe=False)
+    b: B = ormar.ForeignKey(to=B, ondelete=ormar.ReferentialAction.CASCADE)
+
+
 @pytest.fixture(autouse=True, scope="module")
 def create_test_database():
     metadata.drop_all(engine)
@@ -53,3 +83,28 @@ def test_simple_cascade():
     assert fks[0]["constrained_columns"][0] == "artist"
     assert fks[0]["referred_columns"][0] == "id"
     assert fks[0]["options"].get("ondelete") == "CASCADE"
+
+
+def test_validations_referential_action():
+    CASCADE = ormar.ReferentialAction.CASCADE.value
+
+    assert validate_referential_action(None) == None
+    assert validate_referential_action("cascade") == CASCADE
+    assert validate_referential_action(ormar.ReferentialAction.CASCADE) == CASCADE
+
+    with pytest.raises(ormar.ModelDefinitionError):
+        validate_referential_action("NOT VALID")
+
+
+@pytest.mark.asyncio
+async def test_cascade_clear():
+    async with database:
+        async with database.transaction(force_rollback=True):
+            a = await A.objects.create(name="a")
+            b = await B.objects.create(name="b", a=a)
+            c = await C.objects.create(name="c", b=b)
+
+            await a.bs.clear(keep_reversed=False)
+
+            assert await B.objects.count() == 0
+            assert await C.objects.count() == 0