Dzmitry Dzmitry - 1 month ago 17
Java Question

How do I join tables on non-primary key columns?

I have an issue with join tables on an object in an ORM class hierarchy where the join column is NOT the primary key of the base class due a lagacy database structure.
Here is an example of the table design:

CREATE TABLE "SCH"."FOO"
(
"OWNERID" NUMBER(10,0) NOT NULL ENABLE,
"FOOID" NUMBER(10,0) NOT NULL ENABLE,
CONSTRAINT "FOO_PK" PRIMARY KEY ("OWNERID", "FOOID")
CONSTRAINT "FOO_FK1" FOREIGN KEY ("OWNERID") REFERENCES "SCH"."OWNERS" ("OWNERID") ENABLE
)

CREATE TABLE "SCH"."BAR"
(
"BARID" NUMBER(10,0) NOT NULL ENABLE,
"FOOID" NUMBER(10,0)
CONSTRAINT "BAR_PK" PRIMARY KEY ("BARID")
)


And here are the mappings (unesessary infomation removed)

@Entity
@IdClass(FooId.class)
@Table(name = "FOO")
public class Foo implements java.io.Serializable
{
@Id
@Column(name = "OWNERID")
private BigInteger ownerId;

@Id
@SequenceGenerator(name = "FOO_GENERATOR", sequenceName = "SEQ_FOO")
@GeneratedValue(generator = "FOO_GENERATOR")
@Column(name = "FOOID")
private BigInteger id;

@OneToMany(fetch = FetchType.LAZY)
@JoinColumn(name = "FOOID", referencedColumnName = "FOOID")
@Fetch(value = FetchMode.SUBSELECT)
@Cascade(value = {CascadeType.ALL})
private Set<Bar> bar = new LinkedHashSet<Bar>(0);
}


@Entity
@Table(name = "BAR")
public class Bar implements java.io.Serializable
{
@Id
@Column(name = "BARID")
private BigInteger id;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "FOOID", referencedColumnName = "FOOID")
private Foo foo;
}


This fails with an exception:

Caused by: org.hibernate.AnnotationException: referencedColumnNames(FOOID) of com.package.Bar.foo referencing com.package.Foo not mapped to a single property
at org.hibernate.cfg.BinderHelper.createSyntheticPropertyReference(BinderHelper.java:204)
at org.hibernate.cfg.ToOneFkSecondPass.doSecondPass(ToOneFkSecondPass.java:114)
at org.hibernate.cfg.Configuration.processEndOfQueue(Configuration.java:1580)
at org.hibernate.cfg.Configuration.processFkSecondPassInOrder(Configuration.java:1503)
at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1419)
at org.hibernate.cfg.Configuration.buildMappings(Configuration.java:1375)


Could you please help with a solution?

Answer

You must not map the bidirectional association twice. The One side must be marked as the inverse of the Many side, using the mappedBy attribute:

@OneToMany(fetch = FetchType.LAZY, mappedBy = "foo")
@Fetch(value = FetchMode.SUBSELECT)
@Cascade(value = {CascadeType.ALL})
private Set<Bar> bar = new LinkedHashSet<Bar>(0);

...

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "FOOID", referencedColumnName = "FOOID")
private Foo foo;

There is no reason to tell Hibernate twice that the association is mapped by the join column FOOID. And doing it is actually an error, because it defines two different unidirectional associations rather than one bidirectional association.

EDIT

The above should work, but doesn't due to the following Hibernate bug: It's a Hibernate bug. See HHH-4284.

To circumvent this problem, since the FOOID is enough to ensure uniqueness, a solution would be to remove the @Id annotation from the owner ID and the @IdClass annotation.

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