Flask migrate cannot detect db String() equal length change

modify migrations Under the env.py Add parameter compare_type = True

context.configure(connection=connection,
     target_metadata=target_metadata,
     process_revision_directives=process_revision_directives,
     compare_type = True,   #compare_type The default is False, Do not detect data changes 
     compare_server_default = True, # The default value is 
     **current_app.extensions['migrate'].configure_args)

Remember to be in online Inside , The corresponding first parameter is connection

When the update is complete

python manage.py db migrate
python manage.py db upgrade

If you make a mistake , Add

render_as_batch = True

Then delete versions All versions below , If you make a mistake , Delete data==schemas==main==alembic_version The corresponding version number

Re execution

python manage.py db migrate
python manage.py db upgrade