Optimize QuerydslJpaPredicateExecutor.exists.

Fixes #2333
Original pull request #2373

Author: quaff

src/main/java/org/springframework/data/jpa/repository/support/QuerydslJpaPredicateExecutor.java

@@ -37,6 +37,7 @@
 import com.querydsl.core.types.EntityPath;
 import com.querydsl.core.types.OrderSpecifier;
 import com.querydsl.core.types.Predicate;
+import com.querydsl.core.types.dsl.Expressions;
 import com.querydsl.core.types.dsl.PathBuilder;
 import com.querydsl.jpa.JPQLQuery;
 import com.querydsl.jpa.impl.AbstractJPAQuery;
@@ -176,7 +177,7 @@ public long count(Predicate predicate) {
 	 */
 	@Override
 	public boolean exists(Predicate predicate) {
-		return createQuery(predicate).fetchCount() > 0;
+		return createQuery(predicate).select(Expressions.ONE).fetchFirst() != null;
 	}
 
 	/**