Spring JPA使用Tips

Posted 2020-12-09 又是火星人

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命名查询的前缀定义可以在PartTree类找到，

package org.springframework.data.repository.query.parser;

public class PartTree implements Streamable<OrPart> {
    // ...
    private static final String QUERY_PATTERN = "find|read|get|query|stream";
    private static final String COUNT_PATTERN = "count";
    private static final String EXISTS_PATTERN = "exists";
    private static final String DELETE_PATTERN = "delete|remove";
    // ...
}

1、count和exists前缀让我们可以使用命名查询获取查询结果；

@Query(" select count(t) from FollowerInfo t where investUserId = :invUserId")
Integer findFollowerNumberByInvUserId(@Param("invUserId") Long invUserId);

// 效果等同于
Long countByInvestUserId(Long investUserId);

2、stream和Pageable可以优化程序的内存占用(类似Python的生成器)

public interface UserRepository extends JpaRepository<User, Integer> {
    // ...
    Page<User> findAll(Pageable pageable);
    // ...
}

public interface UserRepository extends JpaRepository<User, Integer> {
    // ...
    Stream<User> findAllByName(String name);
    // ...
}

3、Optional可以有效解决Null值问题

public interface UserRepository extends JpaRepository<User, Integer> {
     
    Optional<User> findOneByName(String name);
     
}

4、xxxxxxxxx