19、Java Persistence Query Language (JPA QL) Guide

Java Persistence Query Language (JPA QL) Guide

1. Handling Non - Unique Results

When querying in Java Persistence, there’s a risk of getting a NonUniqueResultException . For example, if you search for all employees named ‘Dave’, there could be multiple matches. To avoid this exception, you can use the getResultList() method:

Query query = entityManager.createQuery(
    "from Employee e where e.name='Dave'");
java.util.List<?> bills = query.getResultList();

The getResultList() method returns an empty list if no matching results are found, instead of throwing an exception.

2. Query Parameters

JPA QL allows you to specify parameters in