Usage of LinkingObject

Question

I don't know how to use LinkingObject in below situation.

class Message: Object{
       ...
      dynamic fromUser : User?
      dynamic toUser : User?
}

class User: Object {
      ....
      let messages = List<Message>()
}

messages should has whole sent and received message. How can I use LinkingObject? Thanks.

Answer 1

From the Docs:

With linking objects properties, you can obtain all objects that link to a given object from a specific property.

In your case I guess you want to get all linked Users in your Message instances, so you can define LinkingObjects like that:

class Message: Object {
      dynamic var fromUser : User?
      dynamic var toUser : User?

      let users = LinkingObjects(fromType: User.self, property: "messages")
}

Otherwise if you need to get all messages from or to user, you can use LinkingObjects this way:

class Message: Object {
    dynamic var fromUser : User?
    dynamic var toUser : User?
}

class User: Object {
    let fromMessages = LinkingObjects(fromType: Message.self, property: "fromUser")
    let toMessages = LinkingObjects(fromType: Message.self, property: "toUser")
}

user.fromMessages will contain all Messages with fromUser == user.

Please check out the Relationships section in the Docs for more info.