Spring JPA one-to-many relationship return null on update - spring

Question

I have a one-to-many relationship between AcademicYear and subject (One AcademicYear has many Subjects).
Here is the model for AcademicYear:
package com.sms.entity;
import javax.persistence.*;
import com.fasterxml.jackson.annotation.JsonManagedReference;
import org.hibernate.annotations.UpdateTimestamp;
import io.swagger.v3.oas.annotations.media.Schema;
import lombok.*;
import java.util.Date;
import java.util.Set;
#Entity
#Setter
#Getter
#Table(name = "academic_years")
#NoArgsConstructor
#AllArgsConstructor
public class AcademicYear {
public AcademicYear(long id, String name, Date updatedAt) {
this.id = id;
this.name = name;
this.updatedAt = updatedAt;
}
#Schema(description = "Unique identifier of the academic year.", example = "1")
#Id
#Column(name = "id")
#GeneratedValue(strategy = GenerationType.IDENTITY)
private long id;
#Schema(description = "Name of the Academic Year.", example = "First Year Primary", required = true)
#Column(name = "name")
private String name;
#JsonManagedReference
#OneToMany(mappedBy="academicYear", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private Set<Subject> subjects;
#UpdateTimestamp
#Column(name = "updated_at", columnDefinition = "TIMESTAMP DEFAULT CURRENT_TIMESTAMP")
private Date updatedAt;
public Set<Subject> getSubjects() {
return subjects;
}
public void setSubjects(Set<Subject> subjects) {
this.subjects = subjects;
}
}
And the model for Subject:
package com.sms.entity;
import javax.persistence.*;
import com.fasterxml.jackson.annotation.JsonBackReference;
import io.swagger.v3.oas.annotations.media.Schema;
import lombok.*;
import org.hibernate.annotations.CreationTimestamp;
import org.hibernate.annotations.UpdateTimestamp;
import java.util.Date;
#Table(name = "subjects")
#Entity
#Setter
#Getter
#NoArgsConstructor
#AllArgsConstructor
public class Subject {
public Subject(long id, String name, Date updatedAt) {
this.id = id;
this.name = name;
this.updatedAt = updatedAt;
}
#Schema(description = "Unique identifier of the subject.", example = "1")
#Id
#Column(name = "id")
#GeneratedValue(strategy = GenerationType.IDENTITY)
private long id;
#Schema(description = "name of the subject.", example = "Mathematics-2")
#Column(name = "name")
private String name;
#ManyToOne(cascade = {CascadeType.ALL})
#JsonBackReference
#JoinColumn(name="academic_year_id", nullable=false)
private AcademicYear academicYear;
#UpdateTimestamp
#Column(name = "updated_at", columnDefinition = "TIMESTAMP DEFAULT CURRENT_TIMESTAMP")
private Date updatedAt;
}
When I try to update name attribute for AcademicYear, I send a PUT request with the following body:
{
"id": 2,
"name": "Second Year"
}
I got the following response:
{
"id": 2,
"name": "Second Year",
"subjects": null,
"updatedAt": "2020-03-27T18:01:16.163+0000"
}
I have subjects as null. This AcademicYear entity already have records, when I send GET request with 2 as pathvariable to get the entity I get the following response:
{
"id": 2,
"name": "Second Year",
"subjects": [
{
"id": 3,
"name": "english",
"updatedAt": "2020-03-27T17:39:09.000+0000"
},
{
"id": 4,
"name": "physics",
"updatedAt": "2020-03-26T21:45:09.000+0000"
},
{
"id": 5,
"name": "chemistry",
"updatedAt": "2020-03-26T21:45:09.000+0000"
},
{
"id": 2,
"name": "math",
"updatedAt": "2020-03-27T17:39:09.000+0000"
}
],
"updatedAt": "2020-03-27T18:01:16.000+0000"
}
I have fetch type as EAGER, don't know why I get subjects as null when I update the entity name. Any help?

Answer 1

You need to use PATCH instead of PUT for partial updates.
Here is why
Based on RFC 7231, PUT should be used only for complete replacement of representation, in an idempotent operation. PATCH should be used for partial updates.
Based on your input, request set null to subjects.
If you still want to use the PUT then you need to provide the whole request object which you want to update/replace
you can find more details here
Why isn't HTTP PUT allowed to do partial updates in a REST API?