Unable to get entity when optional Child OneToOne entity doesn't exist-CodePudding

I've got a situation where we've got a JPA entity TableA that one-to-many joins to TableB and one-to-one joins to TableC & one-to-zero-or-one joins to TableD.

The problem is that when there exists an entry in table_b with a value in table_c_id that doesn't also exist in table_d, when I try to do a get on table_a, I get a 404 instead of the value with a null for table_d.

my entities for table_b and table_d look like this:

@Entity
@Table(name = "table_b")
@IdClass(TableAAndTableCCompositePrimaryKey.class)
public class TableB {
    @Id
    @Column(name = "table_a_id")
    @Type(type = "uuid-char")
    private UUID tableAId;

    @Id
    @Column(name = "table_c_id")
    @Type(type = "uuid-char")
    private UUID tableCId;

    @OneToOne
    @JoinColumn(name = "table_c_id", insertable = false, updatable = false)
    private TableC tableC;

    @OneToOne
    @JoinColumn(name = "table_c_id", insertable = false, updatable = false)
    private TableD tableD;
}

@Entity
@Table(name = "table_d")
public class TableD {
    @Id
    @Column(name = "table_c_id")
    @Type(type = "uuid-char")
    private UUID tableCId;
}

I was unable to put a FK on table_d because table_d could have a value for table_c_id that isn't in table_b.

I'f i've got the rows:

table_a

aaa

bbb

table_b

aaa,ccc

aaa,ddd

table_c

ccc

ddd

table_d

ddd

and I try and grab TableA where tableAId = aaa, I get back a 404, but if I get TableA by tableAId = bbb it works fine. Any time table_b has a value for table_c_id that doesn't exist I don't get back table_a.

Surprisingly, if I change around the joins so that table_d joins off table_c, which I am able to create a foreign key constraint on, it fixes the issue.

What I'm wondering is why didn't the first situation work? Does JPA require a foreign key relation between two joining entities?

CodePudding user response：

For this purpose, Hibernate has the @NotFound annotation which allows you to control the behavior, when a foreign key column like table_b.table_c_id has a value that has no matching target row. By default, JPA has no such mechanism and thus expects a well formed foreign key relationship. You could theoretically make it work with a @SecondaryTable, though that would mean you can't have a TableD entity.