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Difference between revisions of "EclipseLink/Development/Dynamic/RefactorPhaseIForSparseMerge"
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.source-xml {padding:4px;border:1px solid black;} | .source-xml {padding:4px;border:1px solid black;} | ||
</css> | </css> | ||
+ | __NOTOC__ | ||
== Sparse Merge == | == Sparse Merge == | ||
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</srvc:theInstance> | </srvc:theInstance> | ||
</source> | </source> | ||
− | Note the use of | + | Note the use of <code>xsi:nil</code> to indicate <code>null</code> for our Dog walker's department. |
− | === <code>isSet</code> and <code>DynamicEntity/code> === | + | === <code>isSet</code> and <code>DynamicEntity</code> === |
− | 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. | + | 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. <code>null</code>. |
<source lang="java5"> | <source lang="java5"> | ||
import org.eclipse.persistence.exceptions.DynamicException; | import org.eclipse.persistence.exceptions.DynamicException; | ||
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} | } | ||
</source> | </source> | ||
− | It is helpful to note that the above interface is a subset of the | + | It is helpful to note that the above interface is a subset of the <code>DynamicEntity</code> interface: |
<source lang="java5"> | <source lang="java5"> | ||
//EclipseLink imports | //EclipseLink imports |
Revision as of 14:41, 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 (Template:Ename, Template:Mgr, etc.) will contain Template:Null. Any attempt to merge this with a version retrived 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