Grails 如何保存具有多个多对一关系的GORM对象？

假设我有以下域类的层次结构

class School {
   String name
   static hasMany = [teachers: Teacher, students: Student]
}

class Teacher {
   String name
   static belongsTo = [school: School]
   static hasMany = [students: Student]
}

class Student {
   String name
   static belongsTo = [school: School, teacher: Teacher]
}

我尝试了两种不同的方法来拯救学校，老师和学生

尝试1:

def school = new School(name: "School").save()
def teacher = new Teacher(name: "Teacher", school: school).save()
def student = new Student(name: "Student", school: school, teacher: teacher).save(flush: true)

def school = new School(name: "School")
def teacher = new Teacher(name: "Teacher")
def student = new Student(name: "Student")
teacher.addToStudents(student)
school.addToStudents(student)
school.addToTeachers(teacher)
school.save(failOnError: true, flush: true)

它似乎保存正确，但当我运行时：

println(school.students*.name)

它打印空

所以我决定尝试一种不同的方法

尝试2:

def school = new School(name: "School").save()
def teacher = new Teacher(name: "Teacher", school: school).save()
def student = new Student(name: "Student", school: school, teacher: teacher).save(flush: true)

def school = new School(name: "School")
def teacher = new Teacher(name: "Teacher")
def student = new Student(name: "Student")
teacher.addToStudents(student)
school.addToStudents(student)
school.addToTeachers(teacher)
school.save(failOnError: true, flush: true)

在这里，我尝试了几种保存组合，但我总是得到一个关于必填字段为空的错误。在这种情况下，错误是

JdbcSQLException:列“教师ID”不允许为NULL

---

如果有人能解释我的尝试失败的原因以及创建数据的正确方法，我将不胜感激。

这给了我以下例外情况：JDBCExceptionReporter-NULL不允许用于列“教师ID”；SQL语句：在学生（id、版本、名称、学校id、教师id）中插入值（null、、、、、、？），但这些指令是否将数据保存在联接表中？数据库中“链接数据”将保存在何处？

def school = new School(name: "School").save(flush: true)
def teacher = new Teacher(name: "Teacher")
school.addToTeachers(teacher)
teacher.save(flush: true)
def student = new Student(name: "Student", teacher: teacher)
school.addToStudents(student)