Fix migration to handle existing tables and columns

- Update SQLite foreign key constraint implementation to use batch operations
- Add helper function to detect existing constraints
- Use batch_alter_table context manager for SQLite compatibility
- Improve error handling in downgrade operations for SQLite compatibility
- Add better error messages for debugging

migrations/versions/user_auth_migration.py

@@ -45,6 +45,15 @@ def index_exists(table_name, index_name):
     return index_name in indexes
 
 
+def get_constraint_names(table_name):
+    """Get all constraint names for a table"""
+    conn = op.get_bind()
+    inspector = Inspector.from_engine(conn)
+    if not table_exists(table_name):
+        return []
+    return [fk.get('name', '') for fk in inspector.get_foreign_keys(table_name)]
+
+
 def upgrade():
     # Create users table if it doesn't exist
     if not table_exists('users'):
@@ -83,23 +92,42 @@ def upgrade():
     if not column_exists('todos', 'owner_id'):
         op.add_column('todos', sa.Column('owner_id', sa.Integer(), nullable=True))
     
-    # Create foreign key constraint if it doesn't exist
-    try:
-        op.create_foreign_key('fk_todos_owner_id_users', 'todos', 'users', ['owner_id'], ['id'])
-    except (OperationalError, sa.exc.InternalError):
-        pass
+    # For SQLite, we need to use batch operations to add a foreign key constraint
+    # SQLite doesn't support ALTER TABLE ADD CONSTRAINT, so we need to
+    # use SQLAlchemy's batch operations which recreate the table
+    existing_constraints = get_constraint_names('todos')
+    if 'fk_todos_owner_id_users' not in existing_constraints:
+        try:
+            # Use batch operations to recreate the table with the foreign key
+            with op.batch_alter_table('todos') as batch_op:
+                batch_op.create_foreign_key(
+                    'fk_todos_owner_id_users', 
+                    'users',
+                    ['owner_id'], 
+                    ['id']
+                )
+        except (OperationalError, sa.exc.InternalError) as e:
+            # Log error but allow migration to continue
+            print(f"Warning: Could not create foreign key constraint: {str(e)}")
 
 
 def downgrade():
-    # Try to drop foreign key constraint
-    try:
-        op.drop_constraint('fk_todos_owner_id_users', 'todos', type_='foreignkey')
-    except (OperationalError, sa.exc.InternalError):
-        pass
+    # Try to drop foreign key constraint using batch operations for SQLite
+    existing_constraints = get_constraint_names('todos')
+    if 'fk_todos_owner_id_users' in existing_constraints:
+        try:
+            with op.batch_alter_table('todos') as batch_op:
+                batch_op.drop_constraint('fk_todos_owner_id_users', type_='foreignkey')
+        except (OperationalError, sa.exc.InternalError) as e:
+            print(f"Warning: Could not drop foreign key constraint: {str(e)}")
     
     # Try to drop owner_id column from todos table
     if column_exists('todos', 'owner_id'):
-        op.drop_column('todos', 'owner_id')
+        try:
+            with op.batch_alter_table('todos') as batch_op:
+                batch_op.drop_column('owner_id')
+        except (OperationalError, sa.exc.InternalError) as e:
+            print(f"Warning: Could not drop column: {str(e)}")
     
     # Try to drop indexes on users table
     try: