看起来很好。是否有可能你有一个缓存版本的模型，所以CakePHP仍然假设字段的类型是二进制？

At a glance, your code looks fine. Is it possible you've got a cached version of the model so CakePHP still assumes the field's type is binary?

尝试删除/ app / tmp / cache的内容/ models目录。

Try deleting the content of the /app/tmp/cache/models directory.