Difference between revisions of "EclipseLink/Development/Dynamic/RefactorPhaseIForSparseMerge"

Revision as of 14:43, 18 March 2010

Sparse Merge

Current status

The current DBWS implementation (as of 10/02/18) does not handle SOAP update messages that contain changed-only information. The Update operation (part of CRUD lifecycle) requires 'theInstance' to be fully specified in the SOAPMessage; it would be useful to support an update where - excluding PK fields - only the changed elements are specified

For example, Employee 1111 is assigned a new job 'Dog walker':

<env:Envelope xmlns:env="http://schemas.xmlsoap.org/soap/envelope/">
  <env:Header/>
  <env:Body>
    <srvc:update_empType xmlns:srvc="urn:empService" xmlns:ns1="urn:emp">    
      <srvc:theInstance>
        <ns1:empType>
          <ns1:empno>1111</ns1:empno>   <- primary key
          <ns1:job>Dog walker</ns1:job> <- updated job title
        </ns1:empType>    
      </srvc:theInstance>
    </srvc:update_empType>
  </env:Body>
</env:Envelope>

If this representation of Employee 1111 were to be marshalled into an object, most fields (ename, mgr, etc.) will contain null. Any attempt to merge this with a version retreived from the database would *over-write* committed data with nulls. Because of this, the complete instance must be specified:

<srvc:theInstance>
  <ns1:empType>
    <ns1:empno>1111</ns1:empno>   <- primary key
    <ns1:ename>NORMAN</ns1:ename>
    <ns1:job>Dog walker</ns1:job>   <- only field that changed
    <ns1:mgr>7698</ns1:mgr>
    <ns1:hiredate>1998-09-08T00:00:00.0</ns1:hiredate>
    <ns1:sal>10</ns1:sal>
    <ns1:comm>0.1</ns1:comm>
    <ns1:deptno xsi:nil="true"/>
  </ns1:empType>    
</srvc:theInstance>

Note the use of xsi:nil to indicate null for our Dog walker's department.

isSet and DynamicEntity

One solution to the above problem is to have a way to tell the difference between a field that has not yet been assigned any value vs. null.

import org.eclipse.persistence.exceptions.DynamicException;
 
public interface IsSetable {
 
    public boolean isSet(String propertyName) throws DynamicException;
}

It is helpful to note that the above interface is a subset of the DynamicEntity interface:

//EclipseLink imports
import org.eclipse.persistence.exceptions.DynamicException;
 
public interface DynamicEntity {
 
    public <T> T get(String propertyName) throws DynamicException;
 
    public DynamicEntity set(String propertyName, Object value) throws DynamicException;
 
    public boolean isSet(String propertyName) throws DynamicException;
}

Thus, support for Sparse Merge will initially be done through DynamicEntity's

Changes to DynamicEntity

The current EclipseLink DynamicEntity implementation (as of 10/02/18) sets default values for all fields, which defeats the ability of a merge algorithm to support 'sparse-ness'. Setting default values must be moved out of the 'core' Dynamic Persistence framework and relocated to a Dynamic 'helper' class such as DynamicTypeBuilder or JPADynamicTypeBuilder