如何保存具有多个多对一关系的GORM对象？

Question

比方说，我有以下层次结构的域类。

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式来保存学校，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) 

看来，以节省正常，但是当我运行：

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") 
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，我试过的几种组合节省了，我总是得到一个错误约必填字段为空。在这种情况下，错误是

JdbcSQLException：NULL不允许列“TEACHER_ID”

我将不胜感激，如果有人可以解释为什么我的尝试失败，什么正确的方式去创造数据是。

Answer 1

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)