Grails: How to query objects in many to many mapping?

Asked 2011-06-11T15:29:09.983

Hello I have the follwing domain classes.

class Student {
   int age
   static hasMany = [courses:Course]
}

class Course {
   String name
   static hasMany = [students:Student]
}

I want to find the Students taking Course (with id 1), with age 7.

Could I do that with dynamic finder or criteria builder or HQL?

I do not want to do following as it load all students so inefficient:

def course = Course.get(1);
course.students.findAll{ it.age == 7 }

grails grails-orm grails-domain-class

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1 Answer

-2

You can use a dynamic finder:

def students = Student.findByCourseAndAge(Course.load(1), 7)

By using load() instead of get() you avoid retrieving the whole Course instance and just reference its id.

Another option is HQL:

def students = Student.executeQuery(
   'from Student s where s.course.id = :courseId and s.age = :age',
   [courseId: 1, age: 7])

answered 2011-06-11T16:09:29.697