标准api其中1 <> 1条款

Question

I want the query not to return any values. I can't just not query database, so I'd like to add some unreachable condition to predicates, something like 'where 1 <> 1'. But the CriteriaBuilder.equal() doesn't allow to do that. Is there any way to reach the goal?

Thanks.

Answer 1

How about

CriteriaBuilder.notEqual(CriteriaBuilder.literal(1), 1)

Although, if you know that this shouldn't execute, then using expressions might not be optimal on some RDBMS, if the database can't peek at bind values. I don't know how to do create a JPA Predicate with an inlined 1 <> 1 SQL expression, though...

Answer 2

Javadoc from CriteriaBuilder: "Create a disjunction (with zero disjuncts). A disjunction with zero disjuncts is false."

CriteriaBuilder cb..
Predicate itsFalse = cb.disjunction();

And then generated SQL depends about implementation, Hibernate produces 0=1. Why I prefer this method over other alternatives, is:

1. According documentation it fits perfectly to this use without additional arguments and you kind of guess what it does from name.
2. It is short.

Answer 3

这个怎么样：

CriteriaBuilder.isTrue(CriteriaBuilder.literal(Boolean.FALSE));