One to One relationship mapping JPA SpringBoot implementation error: ids for this class must be manually assigned before calling save()

I am trying to understand the JPA Spring Boot implementation for One-to-One mapping classes and was hoping if anyone could provide me a clear picture.

1. One to One mapping Scenario: Table foo and Table childfoo Foo has the columns foo_id,foo_name, foo_place childfoo has the columnd foo_id(foreignkey of foo table), childfoo_name

Here is the JPA entity implementation I've made so far:

@Entity
@Data
@Table(name = "foo")
public class foo implements Serializable {

/**
 * 
 */
private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "foo_id")
private Integer fooId;

@OneToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
@JoinColumn(name="fooId")
private ChildFoo childFoo;
}

ChildFoo class

@Entity
@Data
@NoArgsConstructor
@EqualsAndHashCode(exclude ="foo")
@Table(name = "childfoo")
public class Childfoo implements Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = -8142203085486540150L;
    
    @Id
    private Integer fooId;

    @OneToOne(cascade = CascadeType.ALL, optional = false, fetch = FetchType.LAZY)
    @PrimaryKeyJoinColumn(name = "foo_id", referencedColumnName = "fooId")
    private Foo foo;
    
    @Column(name="child_name")
     private String childName;

   }

I've created a repository for the Foo and I am using FooRepository.save(foo) in the controller to save the data.

Controller code to add the foo and childfoo:

Foo foo = new Foo();
foo.set...

   ChildFoo childFoo = new ChildFoo();
        childFoo.setChildName("abc");
        childFoo.setFoo(foo);

foo.setChildFoo(childFoo);
fooRepository.save(foo);


 

But I am getting the error:

ids for this class must be manually assigned before calling save().

From your comments it appears you are trying to use a shared primary key strategy where ChildFoo will also use fooId as its own primary key.

If that's the case, then I think you need to update some of your JPA annotations:

@Entity
@Data
@Table(name = "foo")
public class Foo implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "foo_id")
    private Integer fooId;

    @OneToOne(cascade = CascadeType.ALL, mappedBy = "foo")
    private ChildFoo childFoo;

}


@Entity
@Data
@NoArgsConstructor
@EqualsAndHashCode(exclude ="foo")
@Table(name = "childfoo")
public class ChildFoo implements Serializable {

    private static final long serialVersionUID = -8142203085486540150L;
    
    @Id
    @Column(name = "foo_id")
    private Integer fooId;

    @OneToOne(cascade = CascadeType.ALL, optional = false)
    @MapsId // primary key copied from Foo
    @JoinColumn(name = "foo_id")
    private Foo foo;
    
    @Column(name="child_name")
     private String childName;

}

And you may need save the instance of Foo (thereby generating the shared Id) before associating and saving the ChildFoo, but I don't think that's necessary once everything is properly annotated.

Speaking of annotations, I only removed the lazy fetch type from your original annotations to clarify updates. You should be able to include them without any issues.

Additional useful links: Shared primary key with JPA and Spring Boot OneToOne shared primary key - JPA2.0 updates