fix server_default not setting value in defaults, pop server_default fields if set to None, add tests, update docs

tests/test_server_default.py

@@ -0,0 +1,80 @@
+import asyncio
+import time
+from datetime import datetime
+
+import databases
+import pytest
+import sqlalchemy
+from sqlalchemy import func, text
+
+import ormar
+from tests.settings import DATABASE_URL
+
+database = databases.Database(DATABASE_URL, force_rollback=True)
+metadata = sqlalchemy.MetaData()
+
+
+class Product(ormar.Model):
+    class Meta:
+        tablename = "product"
+        metadata = metadata
+        database = database
+
+    id: ormar.Integer(primary_key=True)
+    name: ormar.String(max_length=100)
+    company: ormar.String(max_length=200, server_default='Acme')
+    sort_order: ormar.Integer(server_default=text("10"))
+    created: ormar.DateTime(server_default=func.now())
+
+
+@pytest.fixture(scope="module")
+def event_loop():
+    loop = asyncio.get_event_loop()
+    yield loop
+    loop.close()
+
+
+@pytest.fixture(autouse=True, scope="module")
+async def create_test_database():
+    engine = sqlalchemy.create_engine(DATABASE_URL)
+    metadata.drop_all(engine)
+    metadata.create_all(engine)
+    yield
+    metadata.drop_all(engine)
+
+
+def test_table_defined_properly():
+    assert Product.Meta.model_fields['created'].nullable
+    assert not Product.__fields__['created'].required
+    assert Product.Meta.table.columns['created'].server_default.arg.name == 'now'
+
+
+@pytest.mark.asyncio
+async def test_model_creation():
+    p1 = Product(name='Test')
+    assert p1.created is None
+    await p1.save()
+    await p1.load()
+    assert p1.created is not None
+    assert p1.company == 'Acme'
+    assert p1.sort_order == 10
+
+    date = datetime.strptime('2020-10-27 11:30', '%Y-%m-%d %H:%M')
+    p3 = await Product.objects.create(name='Test2', created=date, company='Roadrunner', sort_order=1)
+    assert p3.created is not None
+    assert p3.created == date
+    assert p1.created != p3.created
+    assert p3.company == 'Roadrunner'
+    assert p3.sort_order == 1
+
+    p3 = await Product.objects.get(name='Test2')
+    assert p3.company == 'Roadrunner'
+    assert p3.sort_order == 1
+
+    time.sleep(1)
+
+    p2 = await Product.objects.create(name='Test3')
+    assert p2.created is not None
+    assert p1.created != p2.created
+    assert p2.company == 'Acme'
+    assert p2.sort_order == 10