【flask-migrate】

Autogenerate will detect:

Table additions, removals.
Column additions, removals.
Change of nullable status on columns.
Change indexes and unique constraints
Change foreign key constraints

Autogenerate optional detect：

Change of column type
Change of server default

two switches：
EnvironmentContext.configure.compare_type
EnvironmentContext.configure.compare_server_default

in env.py add compare_type=True, compare_server_default=True to context.configure.
example:
    context.configure(connection=connection,
                  target_metadata=target_metadata,
                  process_revision_directives=process_revision_directives,
                  compare_type=True,
                  compare_server_default=True,
                  **current_app.extensions['migrate'].configure_args)