@LazyCollection(LazyCollectionOption.EXTRA) Problem

ecmel · **Joined:** Wed May 10, 2006 9:09 am **Posts:** 13

Hello,

I am new to Hibernate and this is my first post in this forum, so please forgive me if my question is silly.

I am using SVN revision 9921 of hibernate-annotations and hibernate 3.2 beta.

I have two Entity classes. Account is a tree structure and Journal is a table structure:

Code:

public class Account {

    @ManyToOne(targetEntity=Account.class)
    private Account parent;

    @OneToMany(mappedBy="parent", targetEntity=Account.class)
    @Cascade({CascadeType.DELETE}) 
    private List<Account> children = new ArrayList<Account>();

    @OneToMany(mappedBy="account", targetEntity=Journal.class)
    @LazyCollection(LazyCollectionOption.EXTRA)     
    @BatchSize(size=20)
    private List<Journal> journals = new ArrayList<Journal>();    

}

public class Journal {

    @ManyToOne(targetEntity=Account.class)
    private Account account;

}

I want to make journals an Extra-Lazy collection.

Getting journals.size() issues a "select count(id)..." query so it seems fine.

But when I access a journal (like journals.get(0) ) all the journals are read from the database and no more queries issued for subsequent access of journals.

Any guidance will be more than welcome.
Thanks in advance.

Ecmel Ercan

ecmel · **Joined:** Wed May 10, 2006 9:09 am **Posts:** 13

Parent class:

Code:

@Entity
public class TestParent implements Serializable {
    
    @Id @GeneratedValue                 
    private Long id;
    
    @OneToMany(mappedBy="parent", targetEntity=TestChild.class) 
    @LazyCollection(LazyCollectionOption.EXTRA)      
    private List<TestChild> children = new ArrayList<TestChild>();    

    public Long getId() {
        return id;
    }

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

    public List<TestChild> getChildren() {
        return children;
    }

    public void setChildren(List<TestChild> children) {
        this.children = children;
    }
    
}

Child class:

Code:

@Entity
public class TestChild implements Serializable {
    
    @Id @GeneratedValue                 
    private Long id;
    
    @ManyToOne(targetEntity=TestParent.class) 
    private TestParent parent; 

    public Long getId() {
        return id;
    }

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

    public TestParent getParent() {
        return parent;
    }

    public void setParent(TestParent parent) {
        this.parent = parent;
    }
    
}

The schema:

Code:

CREATE MEMORY TABLE TESTPARENT(
ID BIGINT GENERATED BY DEFAULT AS IDENTITY(START WITH 1) NOT NULL PRIMARY KEY
)

CREATE MEMORY TABLE TESTCHILD(
ID BIGINT GENERATED BY DEFAULT AS IDENTITY(START WITH 1) NOT NULL PRIMARY KEY,
PARENT_ID BIGINT
)

ALTER TABLE TESTCHILD ADD CONSTRAINT FK2F8AEB8A499EB72D FOREIGN KEY(PARENT_ID) REFERENCES TESTPARENT(ID)

The data:

Code:

INSERT INTO TESTPARENT VALUES(1)
INSERT INTO TESTPARENT VALUES(2)
INSERT INTO TESTCHILD VALUES(1,1)
INSERT INTO TESTCHILD VALUES(2,1)
INSERT INTO TESTCHILD VALUES(3,1)
INSERT INTO TESTCHILD VALUES(4,1)
INSERT INTO TESTCHILD VALUES(5,1)
INSERT INTO TESTCHILD VALUES(6,1)
INSERT INTO TESTCHILD VALUES(7,1)
INSERT INTO TESTCHILD VALUES(8,1)
INSERT INTO TESTCHILD VALUES(9,1)
INSERT INTO TESTCHILD VALUES(10,1)
INSERT INTO TESTCHILD VALUES(11,2)
INSERT INTO TESTCHILD VALUES(12,2)
INSERT INTO TESTCHILD VALUES(13,2)
INSERT INTO TESTCHILD VALUES(14,2)
INSERT INTO TESTCHILD VALUES(15,2)
INSERT INTO TESTCHILD VALUES(16,2)
INSERT INTO TESTCHILD VALUES(17,2)
INSERT INTO TESTCHILD VALUES(18,2)
INSERT INTO TESTCHILD VALUES(19,2)

The code:

Code:

transaction = session.beginTransaction();
List parents = session.createQuery("from TestParent").list();            
transaction.commit();

TestParent parent = (TestParent) parents.get(0);
System.out.println(parent.getChildren().size());
            
for (TestChild child : parent.getChildren()) {
    System.out.println(child.getId());            
}

Generated queries for the above code:

Code:

For getChildren().size():

select count(id) from TestChild where parent_id =?

For child.getId():

select children0_.parent_id as parent2_1_, children0_.id as id1_, children0_.id as id5_0_, children0_.parent_id as parent2_5_0_ from TestChild children0_ where children0_.parent_id=?

The last query is generated only once for the entire loop so the entire collection is loaded into memory on first child access.

ecmel · **Joined:** Wed May 10, 2006 9:09 am **Posts:** 13

I tried to map the classes through xml Hibernate mappings instead of annotations, the result is the same.

TestParent.hbm.xml

Code:

<hibernate-mapping>

    <class name="TestParent" table="TESTPARENT">
        <id name="id" column="ID">
            <generator class="native"/>
        </id>

        <list name="children" lazy="extra">
            <key column="PARENT_ID" />
            <list-index column="id" base="1"/>
            <one-to-many class="TestChild" />
        </list>
                
    </class>
    
</hibernate-mapping>

TestChild.hbm.xml

Code:

<hibernate-mapping>

    <class name="TestChild" table="TESTCHILD">
        <id name="id" column="ID">
            <generator class="native"/>
        </id>
                
        <many-to-one name="parent" column="id" class="TestParent" />        
    
    </class>
  
</hibernate-mapping>

ecmel · **Joined:** Wed May 10, 2006 9:09 am **Posts:** 13

Instead of for loop:

Code:

System.out.println(parent.getChildren().size());
System.out.println(parent.getChildren().get(0).getId());    
System.out.println(parent.getChildren().get(1).getId()); 

This works using hbm.xml files above but not work with annotations.

emmanuel · **Posted:** Tue May 23, 2006 1:20 pm

There is no way to lazy extra a get on a bag collection.
Check the annotations reference documentation on how to use a non bag collection.