🐛 Fix fields marked as "set" in models (#117)

Co-authored-by: Michael Statt <michael.statt@modelyst.io>
Co-authored-by: Sebastián Ramírez <tiangolo@gmail.com>

tests/test_fields_set.py

@@ -0,0 +1,21 @@
+from datetime import datetime, timedelta
+
+from sqlmodel import Field, SQLModel
+
+
+def test_fields_set():
+    class User(SQLModel):
+        username: str
+        email: str = "test@test.com"
+        last_updated: datetime = Field(default_factory=datetime.now)
+
+    user = User(username="bob")
+    assert user.__fields_set__ == {"username"}
+    user = User(username="bob", email="bob@test.com")
+    assert user.__fields_set__ == {"username", "email"}
+    user = User(
+        username="bob",
+        email="bob@test.com",
+        last_updated=datetime.now() - timedelta(days=1),
+    )
+    assert user.__fields_set__ == {"username", "email", "last_updated"}