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Why does Hibernate @OneToOne execute multiple select queries instead of one?


Why does Hibernate @OneToOne execute multiple select queries instead of one?

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Why does Hibernate @OneToOne execute multiple select queries instead of one?
Tag : java , By : Michael Gunderson
Date : December 02 2020, 10:46 PM

wish help you to fix your issue n+1 fetching strategy is default one for Hibernate - just because, as stated in documentation

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Why hibernate perform two queries for eager load a @OneToOne bidirectional association?


Tag : java , By : ponchopilate
Date : March 29 2020, 07:55 AM
I wish this helpful for you Blow, if A and B share The same primary key column where both entities are joined by using their primary key, you should use @PrimaryKeyJoinColumn instead
@Entity
public class A implements Serializable {

    private MutableInt id = new MutableInt();

    private B b;

    public void setIdAsMutableInt(MutableInt id) {
        this.id = id;
    }

    @Id
    @GeneratedValue
    public Integer getId() {
        return id.intValue();
    }

    public void setId(Integer id) {
        this.id.setValue(id);
    }

    /**
      * Any ToOne annotation, such as @OneToOne and @ManyToOne, is EARGELY loaded, by default
      */
    @OneToOne(fetch=FetchType.LAZY)
    @PrimaryKeyJoinColumn
    @Cascade(CascadeType.SAVE_UPDATE)
    public B getB() {
        return b;
    }

    public void setB(B b) {
        b.setIdAsMutableInt(id);

        this.b = b;
    }

}
@Entity
public class B implements Serializable {

    private MutableInt id = new MutableInt();

    private A a;

    public void setIdAsMutableInt(MutableInt id) {
        this.id = id;
    }

    @Id
    public Integer getId() {
        return id.intValue();
    }

    public void setId(Integer id) {
        this.id.setValue(id);
    }

    @OneToOne(fetch=FetchType.LAZY)
    @PrimaryKeyJoinColumn
    public A getA() {
        return a;
    }

    public void setA(A a) {
        this.a = a;
    }

}
A a = new A();
B b = new B();

a.setB(b);

/**
  * b property will be saved because Cascade.SAVE_UPDATE
  */
Serializable id = session.save(a);

b = (B) session
        .createQuery("from B b left join fetch b.a where b.id = :id")
        .setParameter("id", id)
        .list()
        .get(0);

Assert.assertEquals(b.getId(), b.getA().getId());
@Entity
public class A implements Serializable {

    private Integer id;

    private B b;

    @Id
    @GeneratedValue
    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    /**
      * mappedBy="a" means: Look at "a" field / property at B Entity. If it has any assigned value, join us Through B_ID foreign key column
      */
    @OneToOne(fetch=FetchType.LAZY, mappedBy="a")
    /**
      * Table A has a foreign key column called "B_ID"
      */ 
    @JoinColumn(name="B_ID")
    @Cascade(CascadeType.SAVE_UPDATE)
    public B getB() {
        return b;
    }

    public void setB(B b) {
        this.b = b;
    }

}   
@Entity
public class B implements Serializable {

    private Integer id;

    private A a;

    public void setIdAsMutableInt(MutableInt id) {
        this.id = id;
    }

    @Id
    @GeneratedValue
    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    @OneToOne(fetch=FetchType.LAZY)
    public A getA() {
        return a;
    }

    public void setA(A a) {
        this.a = a;
    }

}
A a = new A();
B b = new B();

/**
  * Set up both sides
  * Or use some kind of add convenience method
  */ 
a.setB(b);
b.setA(a);

/**
  * b property will be saved because Cascade.SAVE_UPDATE
  */
Serializable id = session.save(a);

b = (B) session
        .createQuery("from B b left join fetch b.a where b.id = :id")
        .setParameter("id", id)
        .list()
        .get(0);

Hibernate @OneToOne executes multiple queries even with @Fetch(FetchMode.JOIN)


Tag : hibernate , By : Techspirit
Date : March 29 2020, 07:55 AM
hop of those help? Using explicit HQL query "FROM Employee WHERE id = " + 1", Hibernate will not respect the annotated Fetch mode. You would need to specify the join in the HQL query or the fetch mode in the criteria.
Hibernate 3.x ignores the Fetch Mode annotation when you use the Query interface (Session.createQuery) so in this case you have to add an INNER JOIN FETCH clause to the FROM part of your query.

Hibernate does multiple queries on @OneToOne join


Tag : hibernate , By : stu73
Date : March 29 2020, 07:55 AM
around this issue Solution is to ditch the join table and have a direct reference between Test <> Team.
The SQL you are seeing makes sense as Hibernate cannot know that TestTeam will be the same entity referenced by Test and Team.
Test test = .../
test.getTestTeam();//triggers load **where test_id = test.id**
Team team = test.getTestTeam().getTeam();
team.getTestTeam();// triggers load **where team_id = team.id**

Hibernate: Multiple select queries made by Hibernate for Fetch mode Eager


Tag : java , By : Thx1138.6
Date : March 29 2020, 07:55 AM
hope this fix your issue Does EntityB contain a field named entity_a? The name should be exactly as declared in the mappedBy attribute.
In general, JPA providers are required to honor the FetchType.EAGER mode. This seems to be a misconfiguration issue. Even so, while the JPA provider is required to load eager associations eagerly, there is no guarantee it will be done in a single query. There is a Hibernate-specific annotation that can be used as a hint: @Fetch(FetchMode.JOIN). Try it out and see if it works.

Spring JPA + Hibernate OneToOne relationships making n+1 queries


Tag : java , By : Bimal Poudel
Date : March 29 2020, 07:55 AM
Hope this helps I am using Spring Boot, Groovy and JPA/Hibernate to migrate an old application. The only restriction is that the database model must not be changed and I found myself with a weird situation in which a OneOnOne relationship: , I think I've got it!
@OneToOne(fetch=FetchType.EAGER, cascade=CascadeType.ALL)
@JoinColumnsOrFormulas([
   @JoinColumnOrFormula(formula=@JoinFormula(value='CAST(key_field_2 AS INT)'))
])
@NotFound(action=NotFoundAction.IGNORE)
Table2 table2
select t1, t2 from Table1 t1 **join fetch** t1.table2 t2 where t1.itemSource = 'ABC'
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