（未保存）多对多关系中的groovy数据

Question

我的数据域：

 class Course{
List teacherCourse
static hasMany = [courseByMultipleTeacher:TeacherCourse]
}

class Teacher{
    String name
    List teacherForCourses
    static hasMany = [teacherForCourses:TeacherCourse]
}

class TeacherCourse{
Course course
Teacher teacher
static mapping={
            id composite: ['teacher','course']
}

}

在我的控制器中：

save(){
Teacher teacherInst = new Teacher()
teacherInst.name = "T1"
teacherInst.save(flush:true)

Course c1 = Course.findById(3)
Course c2 = Course.findById(4)

def teacherCourseA = new TeacherCourse(teacher:teacherInst, course:c1)
def teacherCourseB = new TeacherCourse(teacher:teacherInst, course:c2)
teacherInst.addToTeacherCourse(teacherCourseA)
teacherInst.addToTeacherCourse(teacherCourseB)
teacherInst.save(flush:true)

//Output is: (unsaved) . Why?
println(Teacher.findById(teacherInst.id).teacherForCourses.get(0));

}

输出 net.school.teacher.TeacherCourse ：（未保存）

教师和教师课程被保存在数据库 (PostgreSQL) 中。每当我尝试从列表中检索值时，都会收到（未保存的）消息。我不确定为什么会这样。任何帮助，将不胜感激。我查了这个link，但无法解决问题。

Answer 1

我认为一个问题出在 TeacherCourse 类的 id 上 - GORM (Hibernate) 需要它自己的单列 id 来处理持久上下文中的实例，在 ORM 中使用复合 id 绝不是个好主意。

让 GORM 有他的 id 并指定课程和老师一起是唯一的：

class TeacherCourse {
    Course course
    Teacher teacher

    static mapping = {
        course unique: 'teacher'
    }
}

在这里你可以检查net.school.teacher.TeacherCourse : (unsaved)是当域实例的id为空时从toString()返回的：

http://jira.grails.org/browse/GRAILS-8072

Answer 2

save(){
 Teacher teacherInst = new Teacher()
 teacherInst.name = "T1"
 teacherInst.save(flush:true)

 Course c1 = Course.findById(3)
 Course c2 = Course.findById(4)

 def teacherCourseA = new TeacherCourse(teacher:teacherInst, course:c1).save(true)
 def teacherCourseB = new TeacherCourse(teacher:teacherInst, course:c2).save(true)

 //TRY!
 println(Teacher.findById(teacherInst.id).teacherForCourses.get(0));

}