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merging returns old value for referenced entity [message #902871]

Mon, 20 August 2012 15:46

Amit B
Messages: 12
Registered: July 2012

Junior Member

public class B{
@Id
@Column(name = "id", nullable = false)
private Integer id;
@Version
private int version;
@Column(name = "name", nullable = false)
private String name;

@Override
public SerializableEntity copy() {
return new B(this);
}

public B() {
}

public B(Integer id) {
this.id = id;
}

public Integer getId() {
return id;
}

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

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}
}

public class A {
@Id
@Column(name = "id", nullable = false)
private Integer id;
@Version
private int version;
@Transient
private Integer B_id = 0;

@ManyToOne(targetEntity = B.class)
@JoinColumn(name = "B_ID", referencedColumnName = "id")
private B b_type;

public B getBType() {
if (b_type == null && B_id != 0) {
b_type = readSingleEntityById(B.class, B_id);
}
return b_type;
}

public void setBType(B ent) {
b_type = ent;
if (b_type != null)
B_id = b_type.getId();
else
B_id = getBTypeId();
}

public Integer getBTypeId() {
if (B_id == 0 && getBType() != null)
B_id = b_type.getId();
return B_id;
}

@Override
public SerializableEntity copy() {
return new A(this);
}

public A() {
}

public Integer getId() {
if (id == null) {
return 0;
} else {
return id;
}
}

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

}

public void saveA(){
try {
UserTransaction u = getUserTransaction();
u.begin();
u.merge(A);
u.commit();
} catch {
code here to catch exception
}
}

public <T> T merge(T ent) {
ent = m_em.merge(ent); ----> Problem
m_em.flush();
addMergedEntityToMyCache(ent);
return ent;
}

I have two entities A and B defined as above. A has a many-to-one relationship to Entity B.
Old Values -
b_id = 2
b_type = obj2_type.

New Values to merge. When I enter the merge method these are correct values for ent object
b_id = 4
b_type = obj4_type.

After the call to m_em.merge() the values in the Entity A are -
b_id = 2
b_type = obj4_type

The database is updated with the correct values. Disabling shared cache does not fix the problem. What am I doing wrong here ? Is the b_id as Transient an issue ?. If yes why ? I shouldn't be getting back stale id but the correct merged entity object.

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Re: merging returns old value for referenced entity [message #903283 is a reply to message #902871]

Wed, 22 August 2012 16:21

Amit B
Messages: 12
Registered: July 2012

Junior Member

Just to clarify above - The behavior I see is that my transient id that is id of the referenced entity in Class A seem to retain old value while the actual referenced entity gets updated after merge. How do I keep the transient id and object in-sync. Any ideas ?

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Re: merging returns old value for referenced entity [message #903593 is a reply to message #903283]

Fri, 24 August 2012 09:08

Chris Delahunt
Messages: 862
Registered: July 2009

Senior Member

Yes, Transient is the problem. Because B_ID is transient, it is not merged or persisted to the database in anyway: it is as if it doesn't exist to JPA.

What is the point of keeping b_id in the entity when you are keeping a reference to B itself? Since the field exists, you might want to remove the @Transient and map it to the "B_ID" field but make it insertable=false, updateable=false so that the ManyToOne still controls the field. Or you can look into post merge events which can be used to fix transient fields after the merge.

Best Regards,
Chris

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Re: merging returns old value for referenced entity [message #904008 is a reply to message #903593]

Mon, 27 August 2012 10:53

Amit B
Messages: 12
Registered: July 2012

Junior Member

Thanks Chris. I am going to add postMerge event and do some testing. We are keeping the b_id so that we can serialize/deserialize it and send it to the Client instead of the entire object. Is this a good way to go about it or you have a better suggestion ?

Thanks

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