Refine username field migration to follow SQLite constraints

migrations/versions/2a3b4c5d6e7f_add_username_field.py

@@ -18,10 +18,8 @@ depends_on = None
 
 def upgrade() -> None:
     # Add username column to user table
-    with op.batch_alter_table('user') as batch_op:
-        batch_op.add_column(sa.Column('username', sa.String(), nullable=True))
-        batch_op.create_index('ix_user_username', ['username'], unique=True)
-        
+    op.add_column('user', sa.Column('username', sa.String(), nullable=True))
+    
     # For existing users, initialize username from email
     # This is just SQL template code - in a real migration with existing data,
     # you would need to handle this appropriately
@@ -30,13 +28,14 @@ def upgrade() -> None:
         WHERE username IS NULL
     """)
     
-    # Now make username non-nullable for future records
+    # Now make username non-nullable for future records and add index
     with op.batch_alter_table('user') as batch_op:
         batch_op.alter_column('username', nullable=False)
+        batch_op.create_index('ix_user_username', ['username'], unique=True)
 
 
 def downgrade() -> None:
     # Remove username column from user table
     with op.batch_alter_table('user') as batch_op:
         batch_op.drop_index('ix_user_username')
-        batch_op.drop_column('username')
+    op.drop_column('user', 'username')