Ability for fine-grained configuration of exclusion of foreign key columns in
FetchPlan
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Key: OPENJPA-701
URL: https://issues.apache.org/jira/browse/OPENJPA-701
Project: OpenJPA
Issue Type: Improvement
Components: jdbc, sql
Affects Versions: 1.1.0
Reporter: Michael Vorburger
Priority: Minor
Currently (v1.1.0), "Even when a direct relation is not eagerly fetched,
OpenJPA selects the foreign key columns and caches the values. This way when
you do traverse the relation, OpenJPA can often find the related object in its
cache, or at least avoid joins when loading the related object from the
database. "
(http://openjpa.apache.org/docs/latest/ref_guide_fetch.html#ref_guide_fetch_impl)
In a domain model with "wide" classes that have lot's of associations = foreign
key columns on some tables, under a use case where you KNOW that you will not
traverse some relations (because you know you'll only access 1-2 of many,
configured by some upper layer, other getters may not even be available to
end-code), it would be nice if the FetchPlan API was extended to allow for more
fine-grained configuration of exclusion / inclusion of foreign key columns.
Design proposal, just an idea, could certainly be implemented differently: For
backward compatibility, the current behaviour would likely have to stay as is.
In addition however, a new method named e.g.
FetchPlan.doNotIncludeAllForeignKeyColumns() [or a more suitable shorter
name... :)] would cause the plan NOT to select any foreign key column by
default. Only FK columns that were explicitly added via addField() would then
be selected; if no fields in the referenced class are specified via another
addField, then only the originating PK column would be included, if any field
in the referenced class are also specified, then the JOIN would happen (as
today - or would this simple API not suffice?). -- Minor: Ideally, an
addField() for the association and another addField() for only the ID/PK
attribute of the related class should not lead to a SQL JOIN either, as the
ID/PK is in the original table of course, even if in the object model it's an
attribute of the related class.
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