当某个字段存在于 MongoDB 文档中，但未在您的 Mongoose 架构中定义时，就会发生这种情况.

This will happen when a field is present in the MongoDB document, but not defined in your Mongoose schema.

因此请务必在您的 ServerModel 架构中将其定义为

So be sure to define it in your ServerModel schema as

ip: String

或者，要访问它，即使它未在您的架构中定义，请使用 get 方法:

Or, to access it even though it's not defined in your schema, use the get method:

console.log(server.get('ip'));