[renatsaf]

Problem

A fully qualified enum literal compared with an attribute is converted through the attribute's mapping (t.status = com.example.Status.DONE binds DONE for @Enumerated(STRING)). The same literal, or an enum parameter, used as an argument of CASE, COALESCE or NULLIF is written as its ordinal or as its bare name (H2):

JPQL	Before
UPDATE Todo t SET t.status = CASE WHEN t.id = 1 THEN <DONE> ELSE <PENDING> END	THEN 1 ELSE 0, stores '1'/'0' without error
UPDATE Todo t SET t.status = COALESCE(NULLIF(t.status, t.status), <DONE>)	binds 1, stores '1' without error
UPDATE Todo t SET t.status = CASE t.id WHEN 1 THEN <DONE> ELSE t.status END	THEN DONE, unknown column
UPDATE Todo t SET t.status = NULLIF(t.status, <DONE>)	binds 1, data conversion error
SELECT t FROM Todo t WHERE t.status = CASE WHEN t.id = 1 THEN <PENDING> ELSE <DONE> END	THEN 0 ELSE 1, conversion error or wrong rows
SELECT t FROM Todo t WHERE COALESCE(t.status, <PENDING>) = <DONE>	binds 0, 1
SELECT t FROM Todo t WHERE NULLIF(t.status, <DONE>) IS NULL	binds 1
SELECT t FROM Todo t WHERE :p = CASE WHEN t.id = 1 THEN t.status ELSE :p END	binds 1

The Criteria API is affected the same way (cb.coalesce, cb.selectCase, cb.nullif).

Root cause

A constant or parameter is converted by localBase.getFieldValue(); with the ExpressionBuilder as local base, Expression.getFieldValue() turns an enum into its ordinal. Only direct operands get the attribute as local base: Expression.from() for a comparison and ExpressionQueryMechanism.prepareUpdateAll() for UPDATE SET (value expressions only). For the functions:

• Expression.from() never passes the attribute to a function operand, and FunctionExpression.setLocalBase() only forwards to the first child.
• UPDATE SET skips a function value.
• FunctionExpression.create() gives every function argument the ExpressionBuilder as local base, so NULLIF does not convert its second argument like its first.
• Without anything on the other side (COALESCE(t.status, <PENDING>) = <DONE>), nothing converts the literal inside the function, and the value compared with the function is converted through the function, which has no mapping.

Fix

FunctionExpression, for CASE, COALESCE and NULLIF (functions whose value is one of their arguments):

• setLocalBase() passes the attribute down to the result arguments (THEN/ELSE results, all COALESCE arguments, both NULLIF arguments).
• getFieldValue() converts through the first attribute result argument.
• normalize() converts a constant or parameter result argument that has no attribute local base through the function's own attribute argument. It is done when normalizing because CASE and COALESCE arguments are added one at a time.
• create(): a constant or parameter NULLIF argument is converted through the other argument when that one is an attribute.

Expression.from() passes the attribute to such a function operand, and ExpressionQueryMechanism sets the local base of such a function assigned in UPDATE SET.

Only an attribute (a query key, a field, or the first attribute result argument of such a function) is ever used as local base. Passing a value down lets local bases reference each other: an early version of this change failed TestQuerySyntaxComparisonTests.testNullIf2_* (?1 = NULLIF(?2, s.strVal1)) with a StackOverflowError in ParameterExpression.getBuilder(), the cycle noted in Expression.from() (3107049). Simple CASE WHEN values keep the operand as local base.

Tests

• New TestQueryEnumFunctionArguments (jse, 14 tests): JPQL UPDATE SET with searched CASE, simple CASE, COALESCE (literal and parameter) and NULLIF; SELECT with CASE, COALESCE on the left of the comparison, NULLIF ... IS NULL, a value on both sides of NULLIF and of CASE; Criteria coalesce, selectCase, nullif in an update. Updates are checked by reading the STATUS column with a native query.
• Derby, this branch with and without the fix: core unit tests (12), eclipselink.core.test SRG (1243), testapps jpql (613), criteria (329), advanced (442), advanced2 (159), eclipselink.jpa.test.jse (783, 33 skipped, including TestQueryCase, TestQueryCoalesce, TestQuerySyntaxComparisonTests, TestCoalesceFunction, TestSimpleCase, TestParameterBinding). Without the fix the 14 new tests fail (9 wrong values or rows, 5 Derby type errors); with the fix all pass, and no other test changed status.

Not covered

These were listed in #2848 but do not depend on the enum mapping; they happen with a String attribute as well:

• H2 rejects COALESCE(?, ?) (Unknown data type: "?"), e.g. t.status = COALESCE(:p, <DONE>). The values are now bound converted.
• In UPDATE ... SET x = COALESCE(:p, ...), getParameterType() of :p is null.
• A SELECT projection of CASE/COALESCE over an enum attribute returns the column value (String), not the enum.

Fixes #2848

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