Adds an optional _id field to an object shaped type, unless the _id field is required on that type. In the case _id is required, this method continues to require_id.向对象形状的类型添加可选的_id字段，除非该类型需要_id字段。如果_id是必需的，则此方法继续require_id。
_id
require_id
Adds an optional _id field to an object shaped type, unless the _id field is required on that type. In the case _id is required, this method continues to require_id.向对象形状的类型添加可选的_id字段，除非该类型需要_id字段。如果_id是必需的，则此方法继续require_id。