如何使用@SqlResultSetMapping将ONE-TO-MANY本机查询结果映射到POJO类中

Question

我正在使用Java和MySql在后端API中工作,我正在尝试在JPA 2.1中使用@SqlResultSetMapping将ONE-TO-MANY本机查询结果映射到POJO类,这是本机查询:

@NamedNativeQuery(name = "User.getAll”, query = "SELECT DISTINCT t1.ID, t1.RELIGION_ID t1.gender,t1.NAME,t1.CITY_ID , t2.question_id, t2.answer_id  FROM user_table t1 inner join user_answer_table t2 on t1.ID = t2.User_ID“,resultSetMapping="userMapping")

而且,这是我的结果SQL映射:

@SqlResultSetMapping(
            name = "userMapping",
            classes = {
                            @ConstructorResult(
                                    targetClass = MiniUser.class,
                                    columns = {
                                            @ColumnResult(name = "id"),
                                            @ColumnResult(name = "religion_id"),
                                            @ColumnResult(name = "gender"),
                                            @ColumnResult(name = "answers"),
                                            @ColumnResult(name = "name"),
                                            @ColumnResult(name = "city_id")

                                    }
                            ),

                            @ConstructorResult(
                                    targetClass = MiniUserAnswer.class,
                                    columns = {
                                            @ColumnResult(name = "question_id"),
                                            @ColumnResult(name = "answer_id")

                                    }
                              )

            })

而且,这是POJO类的实现:(我刚刚删除了构造函数和getter/setter)

MiniUser类

public class MiniUser {

    String id;
    String religionId;
    Gender gender;
    List<MiniUserAnswer> answers;
    String name;
    String city_id;
}

和MiniUserAnswer类

public class MiniUserAnswer {

    String questionId;
    String answerId;
}

我的目标是执行此查询并返回一个列表MiniUser,并在每个MiniUser中:列出他的"答案",这是一个列表MiniUserAnswer.

运行此代码后,我收到此错误:

The column result [answers] was not found in the results of the query.

我知道为什么,这是因为查询select语句中没有"answers"字段.
那么,考虑到性能,我怎样才能完成这样的事情呢？这个答案列表可能达到100.

我非常感谢您的帮助,提前致谢!

Answer 1

查询“SELECT DISTINCT t1.ID, t1.RELIGION_ID t1.gender, t1.NAME, t1.CITY_ID, t2.question_id, t2.answer_id”不会返回名为answers的参数。\n要获取您正在查找的结果，我会使用：

\n\n

选项 1（标准生成器）

\n\n

CriteriaBuilder cb = entityManager.getCriteriaBuilder();\nCriteriaQuery<UserTableEntity> cq = cb.createQuery(UserTableEntity.class);\nRoot<UserTableEntity> rootUserTable = cq.from(UserTableEntity.class);\nJoin<UserTableEntity,UserAnswerTableEntity> joinAnswerTable = rootUserTable.join(rootUserTable_.id) // if the relationship is defined as lazy, use "fetch" instead of "join"\n//cq.where() NO WHERE CLAUSE\ncq.select(rootUserTable)\n\nentityManager.createQuery(cq).getResultList();\n

\n\n

选项 2（命名查询，非本机）

\n\n

@NamedQuery(name = "User.getAll\xe2\x80\x9d, query = "从 UserTableEntityt1 中选择 t1 join 获取 t1.answers)

\n\n

选项 3（实体子图，JPA 2.1 中的新增功能）

\n\n

在用户实体类中：

\n\n

@NamedEntityGraphs({\n    @NamedEntityGraph(name = "graph.User.Answers", attributeNodes = @NamedAttributeNode("answers"))\n})\n

\n\n

在 DAO 中实体管理器中设置提示：

\n\n

EntityGraph graph = this.em.getEntityGraph("graph.User.Answers");\n\nMap hints = new HashMap();\nhints.put("javax.persistence.fetchgraph", graph);\n

\n