Many to Many / Circular reference issue Jackson+Spring+Hibernate - json

Question

Course.java
#Entity
#Table
#JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
public class Course {
#Id
#Column(name = "id")
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
#NotEmpty
private String description;
#ManyToMany(fetch = FetchType.EAGER)
#JoinTable(name = "subject_course", joinColumns = #JoinColumn(name = "subject_id", referencedColumnName = "id"), inverseJoinColumns = #JoinColumn(name = "course_id", referencedColumnName = "id"))
private Set<Subject> subjects = new HashSet<Subject>();
---- getter/setter ----
Subject.java
#Entity
#Table
#JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
public class Subject {
#Id
#Column
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
private String description;
#ManyToMany(mappedBy = "subjects", fetch=FetchType.EAGER)
#Cascade({CascadeType.DELETE, CascadeType.SAVE_UPDATE})
private Set<Course> courses = new HashSet<Course>();
---- getter/setter ----
Request configuration in Spring:
#RequestMapping(value = "/courses", method = RequestMethod.GET)
public #ResponseBody ResponseEntity<?> getAllCourses() {
List<Course> courses = courseService.getAllCourses();
if (courses.isEmpty()) {
return new ResponseEntity<Message>(new Message("error", "No course found!"), HttpStatus.NOT_FOUND);
}
return new ResponseEntity<List<Course>>(courses, HttpStatus.OK);
}
Hibernate Version: 4.2.0.Final
Spring Version: 3.2.8.RELEASE
Jackson:
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.2.4</version>
</dependency>
Expecting O/P
[{
"id": 1,
"description": "BCA",
"subjects":[{
"id":1,
"description":"Physics",
"courses":[1,2,3] //Either show blank array or only ids
}]
},{
"id": 2,
"description": "BSC",
"subjects":[{
"id":1,
"description":"Physics",
"courses":[1,2,3]
}]
},{
"id": 3,
"description": "BA",
"subjects":[{
"id":1,
"description":"Physics",
"courses":[1,2,3]
}]
},]
But getting O/P:
[
{
"id": 1,
"description": "BCA",
"subjects": [
{
"id": 1,
"description": "Math",
"staffs": [],
"courses": [
{
"id": 4,
"description": "BDA",
"subjects": [
1
],
"students": []
},
{
"id": 3,
"description": "BBA",
"subjects": [
1
],
"students": []
},
1
],
"students": []
}
],
"students": [
{
"id": 1,
"name": "",
"age": 0,
"gender": null,
"course": 1,
"subjects": []
}
]
},
3,
4
]
As per actual o/p, it is stopping the recursion at second level. But my requirement is not to repeat the same objects data from child... It means Course must not repeat its data in Subject's course property. Similarly, if call the same from Subject then subject should not repeat Course subject property value. It is better to skip, if can't then just display id values separated by comma.
Please advise how to fix this issue.

Answer 1

You can use #JsonIgnore in the Subject class like this:
#ManyToMany(mappedBy = "subjects", fetch=FetchType.EAGER)
#Cascade({CascadeType.DELETE, CascadeType.SAVE_UPDATE})
#JsonIgnore
private Set<Course> courses = new HashSet<Course>();