How to create bogus Predicate in JPA

Question

Is there any way to create bogus Predicate in JPA? Sort of like this:

CriteriaBuilder cb = em.getCriteriaBuilder;
Predicate pred = cb.isTrue(false);

Almost all the methods of CriteriaBuilder take Expression as parameter. I also tried this to no avail:

Expression<Object> path = cb.coalesce.value(null);
Predicate pred = cb.isNotNull(path);

Obviously it throws NPE, however I thought that this might work, because according to API documentation:

A coalesce expression is equivalent to a case expression that returns null if all its arguments evaluate to null, and the value of its first non-null argument otherwise.

score 9 · Answer 1 · answered Mar 27 '15 at 08:01

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dijunction did not work for me in more complicated query in Eclipselink 2.4.

What did was cb.isTrue(cb.literal(false)) which is as precise representation of false as one can get.

answered Mar 27 '15 at 08:01

pdudits

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Thanks for sharing your solution. 4 years later, and people still search for that :) Strangely enough, I tested the solution proposed by @JB Nizet on EclipseLink and it worked. But that was long time ago. – jFrenetic Mar 28 '15 at 12:33

score 9 · Accepted Answer · answered Sep 05 '11 at 10:16

9

I think a disjunction is what you're looking for. It's false by default, until some real predicate is ored to it.

answered Sep 05 '11 at 10:16

JB Nizet

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yes, disjunction seems to be just what I need. Never worked with them before. Thanks a lot! – jFrenetic Sep 05 '11 at 10:34
Works like a charm in JPA 2.0 with Hibernate 4 – Andrea Ligios Oct 20 '15 at 13:30

How to create bogus Predicate in JPA

2 Answers2