QueryDSL：如何从案例表达式创建谓词？

Question

Using QueryDSL, I want to create a Predicate from a case expression that returns boolean expressions:

public static Predicate examplePredicate(NumberPath<Integer> typePath, DateTimePath<Date> timestampPath) {
    final Expression<Boolean> expr = typePath
        .when(0).then(timestampPath.lt(currentTimestamp()))
        .when(1).then(timestampPath.goe(currentTimestamp()))
        .otherwise(false);
    // How can I create a predicate from expr?
}

All then clauses of the case expression return BooleanExpression s - which implements Predicate - but the expr itself is of type Expression<Boolean> .

How can I create a Predicate (probably a BooleanExpression ) from such a case expression?

Answer 1

You could use a CaseBuilder as follows:

new CaseBuilder()
.when(typePath.intValue().eq(0))
.then(timestampPath.lt(currentTimes‌​tamp()))
...

As noted in the comments to the original question, this generates different SQL to that generated by the original code extract but performs the desired function.