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;
}

我的目标是执行这个查询并返回一个MiniUser列表，并在每个MiniUser中：他的“答案”列表，这是一个MiniUserAnswer列表。

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.

我知道原因，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？此答案列表可能达到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”不返回名为answers的参数。要获得您正在寻找的结果，我将使用：

选项1（Criteria Builder）

CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<UserTableEntity> cq = cb.createQuery(UserTableEntity.class);
Root<UserTableEntity> rootUserTable = cq.from(UserTableEntity.class);
Join<UserTableEntity,UserAnswerTableEntity> joinAnswerTable = rootUserTable.join(rootUserTable_.id) // if the relationship is defined as lazy, use "fetch" instead of "join"
//cq.where() NO WHERE CLAUSE
cq.select(rootUserTable)

entityManager.createQuery(cq).getResultList();

选项2（命名查询，不是本机的）

@NamedQuery（name =“User.getAll”，query =“SELECT t1 FROM UserTableEntityt1 join fetch t1.answers）

备选方案3（实体子图，JPA 2.1中的新内容）

在用户实体类中：

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

在DAO中，在实体管理器中设置提示：

EntityGraph graph = this.em.getEntityGraph("graph.User.Answers");

Map hints = new HashMap();
hints.put("javax.persistence.fetchgraph", graph);