JPA: How to get entity based on field value other than ID?

Question

In JPA (Hibernate), when we automatically generate the ID field, it is assumed that the user has no knowledge about this key. So, when obtaining the entity, user would query

Answer 1

Write a custom method like this:

public Object findByYourField(Class entityClass, String yourFieldValue)
{
    CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
    CriteriaQuery<Object> criteriaQuery = criteriaBuilder.createQuery(entityClass);
    Root<Object> root = criteriaQuery.from(entityClass);
    criteriaQuery.select(root);

    ParameterExpression<String> params = criteriaBuilder.parameter(String.class);
    criteriaQuery.where(criteriaBuilder.equal(root.get("yourField"), params));

    TypedQuery<Object> query = entityManager.createQuery(criteriaQuery);
    query.setParameter(params, yourFieldValue);

    List<Object> queryResult = query.getResultList();

    Object returnObject = null;

    if (CollectionUtils.isNotEmpty(queryResult)) {
        returnObject = queryResult.get(0);
    }

    return returnObject;
}

Answer 2

No, you don't need to make criteria query it would be boilerplate code you just do simple thing if you working in Spring-boot: in your repo declare a method name with findBy[exact field name]. Example- if your model or document consist a string field myField and you want to find by it then your method name will be:

findBymyField(String myField);

Answer 3

This solution is from Beginning Hibernate book:

     Query<User> query = session.createQuery("from User u where u.scn=:scn", User.class);
     query.setParameter("scn", scn);
     User user = query.uniqueResult();