准备服务器端资源来解析消息键。
Prepare the server-side resource to resolve the message key.
params 字段本身就是一个对象，包含有将被传递给服务器端脚本的键/值对。
The params field is itself an object, consisting of key/value pairs that will be passed to the server-side script.
对于一对一关联，开发者必须选择关联的哪一端持有代表另一端的外键(这会向下传给数据库模式)。
For one-to-one associations, developers have to select which end of the association holds the foreign key that represents the other end (this gets propagated down to the database schema).
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