How to create a Composite Key in Hibernate

Points To Remember

• You need to create an Embedded Object to create a composite key in Hibernate.
• You can create use an Embeddable Object as an EmbeddedId in class to make it a composite key.

Create a Composite Key in Hibernate

Suppose we have three classes User, Role and UserRole. In class UserRole we want to have a composite id that will include userId and roleId. Then we will first create an embedded object and then using this we will create a composite key.

Let us first create an Embeddable object and

User.java

package com.ekiras.domain;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "user")
public class User {

 @Id
 @GeneratedValue(strategy=GenerationType.AUTO)
 @Column(name="id")
 private Long id;
 
 @Column(name="email")
 private String email;

 @Column(name="password")
 private String password;

        // GETTERS and SETTERS
}
 

Role.java

package com.ekiras.domain;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="role")
public class Role {

 @Id
 @GeneratedValue(strategy=GenerationType.AUTO)
 @Column(name="id")
 private Long id;
 
 @Column(name="authority")
 private String authority;

 // GETTERS and SETTERS

}

UserRoleEmbed.java

package com.ekiras.embeddeble;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Embeddable;

@Embeddable
public class UserRoleEmbed implements Serializable {

 private static final long serialVersionUID = 1L;

 @Column(name="user_id")
 private Long userId;
 
 @Column(name="role_id")
 private Long roleId;

 // GETTERS and SETTERS
 
}

UserRole.java

package com.ekiras.domain;

import javax.persistence.EmbeddedId;
import javax.persistence.Entity;
import javax.persistence.Table;

import com.ekiras.ekjam.embeddeble.UserRoleEmbed;

@Entity
@Table(name="user_role")
public class UserRole {

 @EmbeddedId
 private UserRoleEmbed userRole;

 // GETTERS and SETTERS
}

So this will create the Composite key for class UserRole that we wanted and it will map key={userId, roleId}

The above image shows the database schema that the above code snippets created.