spring jpa 连表重复 join 解决方案
为了解决 userentity 和 userarchiveentity 之间重复的 userarchive 关联，可以在 specification 中手动指定连接类型。修改后的代码如下：
specification<userentity> specification = (root, query, criteriabuilder) -> {
predicate predicate = criteriabuilder.conjunction();
join<userentity, userarchiveentity> userarchiveentityjoin = root.join("userarchive", jointype.left);
return predicate;
};对于不同的业务场景需要不同的模型关联，spring jpa 无法提供针对不同关联要求的方法重载。可以使用依赖注入来解决此问题：
@Repository
public class UserRepositoryImpl implements UserRepositoryCustom {
@Autowired
private UserRepository userRepository;
@Override
public Page<UserEntity> findAllWithUserArchive(Specification<UserEntity> specification, Pageable pageable) {
EntityGraph<UserEntity> entityGraph = EntityGraph.of(UserEntity.class)
.addSubgraph("userArchive");
return userRepository.findAll(specification, pageable, entityGraph);
}
@Override
public Page<UserEntity> findAllWithUserArchiveAndNation(Specification<UserEntity> specification, Pageable pageable) {
EntityGraph<UserEntity> entityGraph = EntityGraph.of(UserEntity.class)
.addSubgraph("userArchive")
.addSubgraph("userArchive.nation");
return userRepository.findAll(specification, pageable, entityGraph);
}
} 
