CODEWITHSUNDEEP
grailsgrails-orm
ttt
ttt

Reputation: 4004

Grails unidirectional Many-to-Many

I hava Java/JavaEE background and started a Grails project recently.

When I write the domain model, there is a requirement: unidirectional many-to-many. I know how it should be in Jpa/Hibernate. I had a quick search about that in grails and seems it is not supported in Grails and some people suggest using a mapping class (there is no example how should do).

Anyone can give me an example of that or how I should do for this requirement?

For example:

class Teacher {
static hasMany: [students: Student]
}

class Student {
    static belongsTo: Teacher
    static hasMany: [teachers: Teacher]
}

Above code is done using a bi-directional many-to-many in Grails documents. What's the code like for a uni-directional many-to-many?

Also only student can have a teachers reference, in teacher class, it can't get a list of students.

Thanks.

Upvotes: 1

Views: 908

Answers (2)

Xuetao
Xuetao

Reputation: 1

Unidirectional many-to-many relationships is supported by hibernate and possible with Grails:

http://blog.exensio.de/2013/12/unidirectional-many-to-many.html

Upvotes: 0

Visme
Visme

Reputation: 983

I have used three classes like teacher,student, and intermediate class stuteach.From student we can access teachers reference.In teacher side,we cant access students.

class Teacher {
String name

}

class Student {
    String name
    static hasMany      = [teachers:StuTeach]

}

class StuTeach {

    static constraints = {
    }
    static belongsTo    = [teacher:Teacher,student:Student]
}

In bootstrap,

        def t1=new Teacher(name:"t1")
        t1.save(flush:true)
        def t2=new Teacher(name:"t2")
        t2.save(flush:true)

        def stu=new Student(name:"s1")
        stu.save(flush:true)

        def stuteach1=new StuTeach()
        stuteach1.student=stu
        stuteach1.teacher=t1
        stuteach1.save(flush:true)

        def stuteach2=new StuTeach()
        stuteach2.student=stu
        stuteach2.teacher=t2
        stuteach2.save(flush:true)

        stu.addToTeachers(stuteach1)
        stu.addToTeachers(stuteach2)

        stu.save(flush:true)
        println stu.teachers.teacher

Upvotes: 1

Related Questions