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How can I create a foreign key constraint using hibernate annotations?

Posted by: admin December 20, 2017 Leave a comment

Questions:

I am trying to use hibernate annotation for writing a model class for my database tables.

I have two tables each having a primary key User and Question.

@Entity
@Table(name="USER")
public class User 
{
    @Id
    @Column(name="user_id")
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;

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

    // getter and setter
}

Question Table.

@Entity
@Table(name="QUESTION")
public class Questions extends BaseEntity{

    @Id
    @Column(name="question_id")
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int id;

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

    // getter and setter

}

And I have one more table, UserAnswer, which has userId and questionId as foreign keys from the above two tables.

But I am unable to find how I can reference these constraints in the UserAnswer table.

@Entity
@Table(name="UserAnswer ")
public class UserAnswer 
{

    @Column(name="user_id")
    private User user;

    //@ManyToMany
    @Column(name="question_id")
    private Questions questions ;

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

    //getter and setter 
}

Please help me achieve this?
Thanks in advance.

Answers:

@Column is not the appropriate annotation. You don’t want to store a whole User or Question in a column. You want to create an association between the entities. Start by renaming Questions to Question, since an instance represents a single question, and not several ones. Then create the association:

@Entity
@Table(name = "UserAnswer")
public class UserAnswer {

    // this entity needs an ID:
    @Id
    @Column(name="useranswer_id")
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToOne
    @JoinColumn(name = "user_id")
    private User user;

    @ManyToOne
    @JoinColumn(name = "question_id")
    private Question question;

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

    //getter and setter 
}

The Hibernate documentation explains that. Read it. And also read the javadoc of the annotations.

Questions:
Answers:

The @Join column(name="reference_column_name") annotation can be used above that property or field of class that is being referenced from some other entity.