more robust migrations

migrations/versions/c243d6a1843d_add_last_name_to_user_model.py

@@ -32,7 +32,12 @@ def upgrade():
 
 def downgrade():
     # ### commands auto generated by Alembic - please adjust! ###
+    conn = op.get_bind()
+    inspector = inspect(conn)
+    columns = [col['name'] for col in inspector.get_columns('user')]
+    
     with op.batch_alter_table('user', schema=None) as batch_op:
-        batch_op.drop_column('last_name')
+        if 'last_name' in columns:
+            batch_op.drop_column('last_name')
 
     # ### end Alembic commands ###