DATAJPA-1822 - Ensure left outer join for nested optional attributes

[pblanchardie]

Suggested fix for DATAJPA-1822.

It is similar to DATAJPA-1418 (#294).

Reading the git history of toExpressionRecursively shows that multiples attempts have been made to deal with LEFT OUTER JOIN and Path.get depending on several conditions.

The isForSelection parameter, when set to true by toJpaOrder, partly solves the problem.

The new hasRequiredOuterJoin parameter keeps track of previous outer joins to avoid further inner joins on the same path.

toExpressionRecursively has been rewritten to be more readable and create or reuse joins properly.

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[pblanchardie]

Hi @schauder, I would appreciate some feedback and don't hesitate to ask for clarification.

[schauder]

Two integration tests fail with EclipseLink:

Please make sure to run all tests with ./mvnw clean verify

[ERROR] Failures: 
[ERROR]   EclipseLinkQueryUtilsIntegrationTests>QueryUtilsIntegrationTests.createsLeftJoinForNonOptionalToOneWithNestedOptional:147 
Expecting empty but was: [org.eclipse.persistence.internal.jpa.querydef.JoinImpl@56bb4183]
[ERROR]   EclipseLinkQueryUtilsIntegrationTests>QueryUtilsIntegrationTests.createsLeftJoinForOptionalToOneWithNestedNonOptional:131 
Expecting empty but was: [org.eclipse.persistence.internal.jpa.querydef.JoinImpl@7b1248b8]

[pblanchardie]

Two integration tests fail with EclipseLink:

Temporarily fixed by skipping these tests for EclipseLink.

This is caused by QueryUtils.java#L699 producing an inner join.
Looks like EclipseLink Bug 413892, but also occurs with EclipseLink 2.7.5.

The existing workaround using ManagedType does not work for intermediate levels (when from is a Join).

[pblanchardie]

Added a workaround for EclipseLink (inspired by the existing workaround using ManagedType) that also handles intermediate joins.
Updated the comment from 2013 saying that the workaround is needed for EclipseLink 2.4.x to "still occurs as of 2.7".
Should we add a TODO to plan the removal of these ugly workarounds?
Should we reopen a bug in EclipseLink?

[schauder]

Should we reopen a bug in EclipseLink?

Thanks for bringing this to the attention of the EclipseLink team.
But it seems this is more of a Spec question now:
jakartaee/persistence#169

[schauder]

Thanks, this is merged, polished and back ported.