Is Select EXISTS() possible in JPQL?

I'm trying to run a query that checks if some conditions are true and returns a simple boolean result as output. What makes it slightly tricky is that one of the conditions is to test fo开发者_StackOverflow中文版r whether no results are returned for a set of criteria.

I'm currently using JPA-2.0 with hibernate as my provider, backed by MySQL. I have gotten an example query working fine in MySQL, but when trying to get it running in JPQL it flops. The MySQL query looks a bit like this:

Select exists(Select statement with criteria) 
  or not exists(Select statement with criteria);

I also got the same output using CASE, but as JPQL doesn't support that statement.

Anyways, when I try to use a similar query in JPQL I get the error:

"unexpected end of subtree"

which from my understanding means that something is missing in the query. Does anyone have any idea how to fix it?

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You can do a boolean query using a case expression.

As of JPA 2.0 (Java EE 6) you can create a TypedQuery .

String query = "select case when (count(*) > 0)  then true else false end from ......"
TypedQuery<Boolean> booleanQuery = entityManager.createQuery(query, Boolean.class);
boolean exists = booleanQuery.getSingleResult();

In JPA 1.0 (Java EE 5) you must use an untyped query.

Query booleanQuery = entityManager.createQuery(query);
boolean exists = (Boolean) booleanQuery.getSingleResult();

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This answer is obsolete. Please refer to correct answer from Rene Link

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No, it is not possible.

Refer to the JPQL BNF documentation from oracle.

simple_cond_expression ::= comparison_expression | between_expression | like_expression | in_expression | null_comparison_expression | empty_collection_comparison_expression | collection_member_expression | exists_expression

exists_expression ::= [NOT] EXISTS(subquery)

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In a project with Hibernate 5.2 (which supports JPA 2.1), and Spring Data Jpa 2.0.6, I successfully used this JPQL query:

@Query("SELECT COUNT(c) > 0 FROM Contract c WHERE c.person.id = :pid")
Boolean existContractForPerson(@Param("pid") Long personId);

In the logs, I read that the produced native query is the following:

select count(contract0_.contract_id)>0 as col_0_0_ from contracts contract0_ where contract0_.fk_person_id=?

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Alternatively you could use a select count(...) and test whether it returns 0. This should be almost as efficient without requiring to write much more code (in fact, the query itself will probably look simpler).

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You have mismatched brackets. Try removing the one before the not (and the ones around the first exists):

select exists(Select statement with criteria) 
  or not exists(Select statement with criteria);

You don't need brackets around exists()

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In a project that uses

    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-core</artifactId>
        <version>4.2.4.Final</version>
    </dependency>
    ...

I successfully used an

exists(select s.primaryKey from Something s)

clause. So it might have changed. It could also be Hibernate-proprietary. Since a lot of people use Hibernate as a persistence provider, I thought I might add this here.

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It is more efficient for DB not counting all records. Create native query

Spring-Data-JPA

@Query(value = ".....", nativeQuery = true)

or JPA:

@NamedNativeQuery(name=.., query="..", resultClass=..)