JPA学习笔记（13）——查询缓存

使用hibernate的查询缓存

运行下面代码：

String jpql = "FROM User u WHERE u.id = ?";
Query query = entityManager.createQuery(jpql);
query.setParameter(1, 1);
User user = (User) query.getSingleResult();

query = entityManager.createQuery(jpql);
query.setParameter(1, 1);
user = (User) query.getSingleResult();

非常显然会运行两次查询

假设想要使用缓存，仅仅查询一次。能够使用setHint

String jpql = "FROM User u WHERE u.id = ?";
Query query = entityManager.createQuery(jpql).setHint(QueryHints.HINT_CACHEABLE, true);
query.setParameter(1, 1);
User user = (User) query.getSingleResult();

query = entityManager.createQuery(jpql).setHint(QueryHints.HINT_CACHEABLE, true);
query.setParameter(1, 1);
user = (User) query.getSingleResult();

注意：这里的QueryHints是org.hibernate.ejb.QueryHints包下的，而且。使用查询缓存的前提是在配置文件里配置了启用查询缓存

<property name="hibernate.cache.use_query_cache" value="true"/>