grails <g:select> 下拉无法显示正确的值

Question

这个下拉菜单几乎也是我想要的。我无法显示答案对象的body 属性或toString。

<g:select name="questionId"
        from="${questionInstance.answers.id}"
        value="${questionInstance.correctAnswer.id}"
        noSelection="['':'Select a Module']" />

不幸的是，无论我尝试什么组合，我都无法获得下拉菜单，默认情况下，选择correctAnswer，而不使用from 属性中的id。

<g:select name="questionId"
        from="${questionInstance.answers}"
        value="${questionInstance.correctAnswer}"
        noSelection="['':'Select a Module']" />

我做错了什么？

问题

class Question {

    DateTime dateCreated
    DateTime lastUpdated

    String body
    Answer correctAnswer
    Integer ordinal

    static belongsTo = [lesson: Lesson]
    static hasMany = [answers: Answer]

    static constraints = {
        body blank: false
        correctAnswer nullable: true,
                validator: { Answer val, Question obj ->
                // Correct answer must have this as it's question
                val ? val.question == obj : true // TODO: Give this a proper error message
            }
        ordinal unique: 'lesson'
    }

    static mapping = {
        lesson lazy: false
        answers sort: 'ordinal'
    }
}

回答

class Answer {

    DateTime dateCreated
    DateTime lastUpdated

    String body
    Integer ordinal
    String reason

    static belongsTo = [question: Question]

    static constraints = {
        body blank: false
        ordinal unique: 'question'
        reason blank: false
    }

    static mapping = {
        question lazy: false
    }

    String toString() {
        "Answer: $body"
    }
}

Answer 1

我会说，这应该可行：

<g:select name="questionId"
    from="${questionInstance.answers}"
    value="${questionInstance.correctAnswer}"
    optionKey="id"
    optionValue="body"
    noSelection="['':'Select a Module']" />

Answer 2

您能否提供域问题和答案？

同时尝试添加属性 optionKey="id" optionValue="name"

只要域具有名称属性。