docs: def get_binds(self, app=None):
          """Returns a dictionary with a table->engine mapping.
  
          This is suitable for use of sessionmaker(binds=db.get_binds(app)).
          """
          app = self.get_app(app)
          binds = [None] + list(app.config.get('SQLALCHEMY_BINDS') or ())
          retval = {}
          for bind in binds:
              engine = self.get_engine(app, bind)
              tables = self.get_tables_for_bind(bind)
              retval.update(dict((table, engine) for table in tables))
          return retval