I've got three classes:
{code:java}
public class A {
...
@ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.PERSIST)
@JoinColumn(name = "NONPK", referencedColumnName="NONPK")
private C cValue;
...
}
public class B {
...
@ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.PERSIST)
@JoinColumn(name = "NONPK", referencedColumnName="NONPK")
private C cValue;
...
}
public class C {
...
@Id
@Column(name = "ID", unique = true, nullable = false, precision = 10)
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "IDNR")
@NotNull
private Long id;
@Column(name = "NONPK", unique = true, nullable = false, length = 10)
@NotNull
private String nonPk;
...
}
{code}
When I have a query which first loads all entities of class A, with an EntityGraph to collect the entity C in the same query, it creates the entity A without any extra queries. When I load all entities of B, again loaded with an EntityGraph to load C, then an extra query is performed. Both entities have the same entity C with the same NONPK-value.
I’ve traced it to the following:
When A is loaded, it also loads the entity C. Because entity C is not already loaded in the session, it will load it from the resultset. Then it constructs a EntityUniqueKey based on C and A and puts that in the persistanceContext of the session (see Loader.loadFromResultSet). Later when B is loaded, it already sees entity C loaded and does not try to load it again. For B there won’t be a EntityUniqueKey. When it is time to hydrate the relationship, it tries to search for C based on the EntityUniqueKey of C and B (see TwoPhaseLoad.doInitializeEntity and EntityType.resolve, isReferenceToPrimaryKey = false). Because the entity is only available on the key of C and A, it will not find anything, therefore it will issue a query.
It can be reproduced with the provided testcase.
Is it possible to generate a custom EntityUniqueKey, so both A and B will use the same key and the extra query is not issued?
See https://discourse.hibernate.org/t/custom-entityuniquekey-possible/1501. |
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