how to create mutation with foreign key?

[xp13910818313]

I want to create mutation with domain class talk ,how to write the document?

@GrailsCompileStatic
class Speaker {
    String firstName
    String lastName
    String name
    String email
    String bio
    static hasMany = [talks: Talk]
    static graphql = true 
    static constraints = {
        email nullable: true, email: true
        bio nullable: true
    }
    static mapping = {
        bio type: 'text'
        name formula: 'concat(FIRST_NAME,\' \',LAST_NAME)'
        talks sort: 'id'
    }
}

@GrailsCompileStatic
class Talk {
    Speaker speaker
    String title
    int duration
    static graphql = true 
    static belongsTo = [speaker: Speaker]
}

if i use the code like this:

mutation {
  talkCreate(talk: {
    title: "about K8S"
    duration: 120
    speaker: {
        id: 1
    }
  }) {
    id
    title
    duration
    speaker {
        id
    }
    errors {
      field
      message
    }
  }
}

the speaker_id always set null, why？