Improve query result processing with composite pattern
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Key: OPENJPA-1225
URL: https://issues.apache.org/jira/browse/OPENJPA-1225
Project: OpenJPA
Issue Type: New Feature
Reporter: Pinaki Poddar
Query result data are packed into user-visible forms by a ResultPacker.
The logic of data packing is limited to certain extent.
This limitation is obvious if the query projection contains multiple
constructor terms e.g.
"select new foo(p.name, p.age), Bar(p.age, p.name) from PObject p"
The limitation is further highlighted with new (and rather hairy) specification
on result processing in JPA 2.0 via introduction of several methods related to
selection of projection terms namely select(), multiselect(), array(), tuple(),
constructor(). In fact, JavaDoc for CriteriaQuery.multiselect() is a fine
example of an API design following 'design-by-committee' approach.
Data packing result need to improve. The solution is made difficult because
a) it is risky to change the input data structures (the projection terms,
aliases held by QueryExpressions) as they will have wide impact on query
formation.
b) this new data packing should not impact the JPQL based queries or their
result processing.
c) ResultPacker is an implementation not an interface.
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