在获取联接中休眠重载实体

Question

I am having a problem with Hibernate reloading the entities in a query even though they are being fetched as part of the main query.

The entities are as follows (simplified)

class Data {
    @Id
    String guid;

    @ManyToOne(fetch = FetchType.LAZY)
    @NotFound(action = NotFoundAction.IGNORE)
    DataContents contents; 
}

class DataClosure {
    @Id
    @ManyToOne(fetch = FetchType.EAGER)
    @Fetch(FetchMode.JOIN)
    @JoinColumn(name = "ancestor_id", nullable = false)
    private Data ancestor;

    @Id
    @ManyToOne(fetch = FetchType.EAGER)
    @Fetch(FetchMode.JOIN)
    @JoinColumn(name = "descendant_id", nullable = false)
    private Data descendant;

    private int length;
}

This is modelling a closure table of parent / child relationships.

I have set up some criteria as follows

    final Criteria criteria = getSession()
            .createCriteria(DataClosure.class, "dc");
    criteria.createAlias("dc", "a");
    criteria.createAlias("dc.descendant", "d");
    criteria.setFetchMode("a", FetchMode.JOIN);
    criteria.setFetchMode("d", FetchMode.JOIN);
    criteria.add(Restrictions.eq("d.metadataGuid",guidParameter));
    criteria.add(Restrictions.ne("a.metadataGuid",guidParameter));

This results in the following SQL query

select
    this_.descendant_id as descenda2_21_2_,
    this_.ancestor_id as ancestor3_21_2_,
    this_.length as length1_21_2_,
    d2_.guid as metadata1_20_0_,
    d2_.name as name5_20_0_,
    a1_.guid as metadata1_20_1_,
    a1_.name as name6_20_1_
from
    data_closure this_ 
inner join
    data d2_ 
        on this_.descendant_id=d2_.metadata_guid 
inner join
    data a1_ 
        on this_.ancestor_id=a1_.metadata_guid 
where
    d2_.guid=? 
    and a1_.guid<>?

which looks like it is correctly implementing the join fetch. However when I execute

    List list = criteria.list();

I see one of these entries in the SQL log per row in the result set

Result set row: 0
DEBUG Loader  - Loading entity: [Data#testGuid19]
DEBUG SQL  - 
select
    data0_.guid as guid1_20_0_,
    data0_.title as title5_20_0_,
from
    data data0_ 
where
    data0_.guid=?
Hibernate: 
   (omitted)
DEBUG Loader  - Result set row: 0
DEBUG Loader  - Result row: EntityKey[Data#testGuid19]
DEBUG TwoPhaseLoad  - Resolving associations for [Data#testGuid19]
DEBUG Loader  - Loading entity: [DataContents#7F1134F890A446BBB47F3EB64C1CF668]
DEBUG SQL  - 
select
    dataContents0_.guid as guid_12_0_,
    dataContents0_.isoCreationDate as isoCreat2_12_0_,
from
    dataContents dataContents0_ 
where
    dataContents0_.guid=?
Hibernate: 
    (omitted)

It is looks like even though the DataContents is marked as lazily loaded, it's being loaded eagerly.

So I either want some way in my query to fetch join DataClosure and Data and lazily fetch DataContents, or to fetch join the DataContents if that is not possible.

Edit:

Modelling the closure table like this

class DataClosure {
    @Id
    @Column(name = "ancestor_id", nullable = false, length =36 )
    private String ancestorId;

    @Id
    @Column(name = "descendant_id", nullable = false, length =36 )
    private String descendantId;

    @ManyToOne(fetch = FetchType.EAGER)
    @Fetch(FetchMode.JOIN)
    @JoinColumn(name = "ancestor_id", nullable = false)
    private Data ancestor;

    @ManyToOne(fetch = FetchType.EAGER)
    @Fetch(FetchMode.JOIN)
    @JoinColumn(name = "descendant_id", nullable = false)
    private Data descendant;

    private int length;
}

fixed the problem. In other words, having @Id annotation on entities from other tables seemed to cause the issue, even though there was nothing wrong with the queries generated.

Answer 1

I think your problem here might be this

@NotFound(action = NotFoundAction.IGNORE)

There are plenty of google results where using that causes the lazy loading to become eager. I think it is a bug in Hibernate.

Adding this to the list of annotations should fix the problem

@LazyToOne(value=LazyToOneOption.NO_PROXY)

Since that informs Hibernate that you will not try to use that property later on so no proxy is required.