java - 将 JPA Criteria Builder 与表连接结合使用

Question

我正在尝试使用 JPA Criteria Builder 连接两个表:Country 和 Geotarget。等效的 SQL 是

Select distinct Country.* from Country Inner Join Geotarget
 where Geotarget.Country_ID = Country.ID;

我的代码是

     CriteriaBuilder criteriaBuilder getTransactionalEntityManager().getCriteriaBuilder();
    CriteriaQuery<Country> criteriaQuery = criteriaBuilder.createQuery(Country.class);
    Root<Country> root = criteriaQuery.from(Country.class);
    Join<Geotarget, Country> geotargetJoin = root.join(Geotarget_.country, JoinType.INNER);
    Predicate predicate = criteriaBuilder.equal(Country_.id,Geotarget_.country);
    criteriaQuery = criteriaQuery.where(predicate);
    criteriaQuery.select(Country.class).distinct(true);
    return findAllObjects(criteriaQuery);

但这是错误的，它甚至没有在某些地方进行解析。特别是我似乎找不到连接线或等于原因的代码，因为它似乎不喜欢比较两个字段。你能用正确的代码帮助我吗？

Answer 1

我认为您不需要谓词。连接本身应执行 GeoTarget.Country_ID = Country.ID。因此修改为:

CriteriaBuilder criteriaBuilder getTransactionalEntityManager().getCriteriaBuilder();
CriteriaQuery<Country> criteriaQuery = criteriaBuilder.createQuery(Country.class);
Root<Country> root = criteriaQuery.from(Country.class);
Join<Geotarget, Country> geotargetJoin = root.join(Geotarget_.country); // Default is inner
criteriaQuery.select(Country.class).distinct(true);
return findAllObjects(criteriaQuery);