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From "Pinaki Poddar" <ppod...@bea.com>
Subject RE: [jira] Commented: (OPENJPA-245) Attach NEW and auto-increment identity
Date Tue, 29 May 2007 22:50:37 GMT
Hello Aleksandar, 
> This use case is so common, I am surprised that nobody had encountered
this problem before. OpenJPA documentation tells me it should be 
> possible.
If to be merged instance is a clone created by
serialization+deserialization -- then OpenJPA detects the update even
without any version field and "does the right thing". I think your issue
raised the use case where to be merged instance is a 'copy' of another
persistent object created by Java new() followed by field-by-field copy
of the state. This makes OpenJPA to decide the instance as a new
instance rather than a detached instance.

However, others may suggest ways to do what your use case requires. 


Pinaki Poddar
BEA Systems
415.402.7317  


-----Original Message-----
From: Aleksandar Likic [mailto:alikic@rogers.com] 
Sent: Tuesday, May 29, 2007 2:08 PM
To: open-jpa-dev@incubator.apache.org
Subject: Re: [jira] Commented: (OPENJPA-245) Attach NEW and
auto-increment identity


>From the documentation, I don't see that merge() requires a version
field for it to function the way I want. The use case is simple - a web
service that updates an existing record in database which doesn't have
associated version id. This use case is so common, I am surprised that
nobody had encountered this problem before. OpenJPA documentation tells
me it should be possible.

Here is copy/paste from OpenJPA documentation. Pay attention to the last
bullet point ("If neither of the above cases apply...").

1.2.  Attach Behavior

When attaching, OpenJPA uses several strategies to determine the optimal
way to merge changes made to the detached instance. As you will see,
these strategies can even be used to attach changes made to a transient
instance which was never detached in the first place.

    * If the instance was detached and detached state is enabled,
OpenJPA will use the detached state to determine the object's version
and primary key values. In addition, this state will tell OpenJPA which
fields were loaded at the time of detach, and in turn where to expect
changes. Loaded detached fields with null values will set the attached
instance's corresponding fields to null.

    * If the instance has a Version field, OpenJPA will consider the
object detached if the version field has a non-default value, and new
otherwise.

      When attaching null fields in these cases, OpenJPA cannot
distinguish between a field that was unloaded and one that was
intentionally set to null. In this case, OpenJPA will use the current
detach state setting to determine how to handle null fields: fields that
would have been included in the detached state are treated as loaded,
and will in turn set the corresponding attached field to null.

    * If neither of the above cases apply, OpenJPA will check to see if
an instance with the same primary key values exists in the database. If
so, the object is considered detached. Otherwise, it is considered new. 


JIRA jira@apache.org wrote:
> 
> 
>     [
> https://issues.apache.org/jira/browse/OPENJPA-245?page=com.atlassian.j
> ira.plugin.system.issuetabpanels:comment-tabpanel#action_12499851
> ]
> 
> Pinaki Poddar commented on OPENJPA-245:
> ---------------------------------------
> 
> 
> merge() to identify that the the merged entity instance is not 
> *truely* new but a version of a instance that is already persistent, 
> the entity requires a version field.
> If the merged instance was a clone created out of serialization and 
> desrialization, then OpenJPA will maintain the required bits to 
> identify the difference between a truly new instance and an instance 
> that has been detached.
> 
> 
> 
>> Attach NEW and auto-increment identity
>> --------------------------------------
>>
>>                 Key: OPENJPA-245
>>                 URL:
https://issues.apache.org/jira/browse/OPENJPA-245
>>             Project: OpenJPA
>>          Issue Type: Bug
>>          Components: jpa
>>    Affects Versions: 0.9.6, 0.9.7
>>         Environment: jdk1.5.0_11, Win XP, Fedora Core 6, Postgres 8.1

>> (on
>> Fedora)
>>            Reporter: Aleksandar Likic
>>
>> According to documentation (1.2 Attach Behavior), when an entity 
>> instance is NEW (never detached):
>>     * If neither of the above cases apply, OpenJPA will check to see 
>> if an instance with the same primary key values exists in the 
>> database. If so, the object is considered detached. Otherwise, it is
considered new.
>> This doesn't work for me - a new record in database is created on 
>> commit instead of updating the existing one. The "regular" case - 
>> detach/modify/attach works fine - the existing record is updated.
>> It is very easy to reproduce - just create a new instance of an 
>> entity, assign an already existing primary key, call em.merge() and 
>> commit. A new record will be created in database, with new,
auto-generated primary key.
>> I stumbled on this trying to implement a web service that uses 
>> OpenJPA-based backend. When servicing an "update" request, the web 
>> service instantiates a NEW object (by performing XML 
>> de-serialization) and calls em.merge to update the entity. A new 
>> record gets created instead of updating an existing one.
>> ------------ Entity class (START) ------------------------------ 
>> package exaple; public class Consumer implements java.io.Serializable

>> {
>>   private long id;
>>   public long getId() {
>>     return this.id;
>>   }
>>   public void setId(long id) {
>>     this.id = id;
>>   }
>>   private java.lang.String firstName;
>>   public java.lang.String getFirstName() {
>>     return this.firstName;
>>   }
>>   public void setFirstName(java.lang.String firstName) {
>>     this.firstName = firstName;
>>   }
>>   private java.lang.String lastName;
>>   public java.lang.String getLastName() {
>>     return this.lastName;
>>   }
>>   public void setLastName(java.lang.String lastName) {
>>     this.lastName = lastName;
>>   }
>> ------------ Entity class (END) ------------------------------
>> ------------ persistence.xml (START) ------------------------------ 
>> <?xml version="1.0" encoding="UTF-8"?> <persistence 
>> xmlns="http://java.sun.com/xml/ns/persistence"
>> xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.0">
>>     <persistence-unit name="example" 
>> transaction-type="RESOURCE_LOCAL">
>>     
>>        
>>
<provider>org.apache.openjpa.persistence.PersistenceProviderImpl</provid
er>
>>         <!-- We must enumerate each entity in the persistence unit
-->
>>         <class>example.Consumer</class>
>>         <properties>
>>             <property name="openjpa.jdbc.DBDictionary"
value="postgres"/>
>>             <property name="openjpa.ConnectionDriverName"
>> value="org.postgresql.Driver"/>
>>             <property name="openjpa.ConnectionUserName"
>> value="app_user"/>
>>             <property name="openjpa.ConnectionPassword"
>> value="app_user"/>
>>             <property name="openjpa.ConnectionURL"
>> value="jdbc:postgresql://localhost/alikic"/>
>>             <property name="openjpa.Log"
>> value="DefaultLevel=WARN,SQL=TRACE"/>
>>             
>>         </properties>
>>     </persistence-unit>
>>     
>> </persistence>
>> ------------ persistence.xml (END) ------------------------------
>> ------------ orm.xml (START) ------------------------------ 
>> <entity-mappings xmlns="http://java.sun.com/xml/ns/persistence/orm"
>>     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
>>     xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm
>> orm_1_0.xsd"
>>     version="1.0">
>>     <entity class="example.Consumer">
>>         <attributes>
>>             <id name="id">
>>                 <generated-value strategy="IDENTITY"/>
>>             </id>
>>             <basic name="firstName">
>>                 <column name="first_name"/>
>>             </basic>
>>             <basic name="lastName">
>>                 <column name="last_name"/>
>>             </basic>
>>         </attributes>
>>     </entity>
>> </entity-mappings>
>> ------------ orm.xml (END) ------------------------------
> 
> --
> This message is automatically generated by JIRA.
> -
> You can reply to this email to add a comment to the issue online.
> 
> 
> 

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-auto-increment-identity-tf3823771.html#a10860565
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