JPA one-to-one mapping creates an extra column. How to remove it?-CodePudding

I have one-to-one mapping JPA table in my springboot application which works fine. The Users is the parent table and in the account_no column, it stores the foreign key. Which is, child's primary key. The child is Account table.

However, when the application is started, I can see that there is one additional column (user_id) that has been created in H2 DB. I think it is something wrong with my JPA mapping. Pls help to figure it out. Below are the two classes.

@Entity
public class User extends AbstractEntity {

    // Other fields related to user entity go here ..

    @OneToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "account_no", referencedColumnName = "account_num")
    private Account account;
}

@Entity
public class Account extends AbstractEntity{

    // fields like account#, balance etc goes here..

    @Column(name="account_num", unique = true)
    @NotNull
    private long accountNo;

    @OneToOne (fetch = FetchType.LAZY)
    private User user;
}

Startup log.

 create table account (id bigint not null,  account_num bigint not null, bal float not null, user_id bigint, primary key (id))
2021-12-22 00:09:28.765 DEBUG 25380 --- [           main] org.hibernate.SQL                        :

CodePudding user response：

Decide which side should contain the extra column and use the mappedBy attribute. Then JPA will do what's needed

@OneToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY, optional = false, mappedBy = "user")
private Account account;

Considering that you have bidirectional mapping you don't need the @JoinColumn that you have used.

Just both @OneToOne annotations and the decision which would be owner entity of the relation by using the mappedBy attribute on one of those annotations.

CodePudding user response：

It depends on you in which side you store the extra column which was a foreign key.Because When You started to established oneToOne relationship between two table it is mandatory to store user's primary key in account table as a foreign key, or account table primary key in user table as foreign key.You should be need to declare mappedBy and your tables reference name.for example if you declare mappedBy="user" in account table it create an extra account_id column in user table as a foreign key, Same as for account

@OneToOne(optional = false, mappedBy = "user")
private Account account;

Don't need to declare these things in side OneToOne annotation cascade = CascadeType.ALL, fetch = FetchType.LAZY, By default it always support lazy fetch