java - 如何在数据库表中查询仅包含两个数据对象的记录列表

Question

我的数据库表如下所示:

ID      ACCESSID    ENTITYGUID      NAME    NAMEID      OWNERGUID   TIMECREATED     VALUEID     VALUETYPE  

我只想检索包含两个字段的列表:name 和 valueId，而不是整个记录。我尝试如下:

通过预测:

public void getAllEntityMetadata(int GUID) {
        Criteria c = session.createCriteria(RevMetadata.class)
                .add(Restrictions.eq("entityGUID", GUID))
                .setProjection(Projections.property("name"))
                .setProjection(Projections.property("nameId"));

        List<RevMetadata> m = (List<RevMetadata>) (RevMetadata) c.list();
        for (RevMetadata item : m) {
            System.out.println("-> All entity metadata for GUID: " + item.getName() + " : " + item.getValueId());
        }
}

我收到错误:

Caused by: java.lang.ClassCastException: java.util.ArrayList cannot be cast to wakiliproject.Persistence.RevMetadata
    at wakiliproject.Persistence.PersistRevMetadata.getAllEntityMetadata(PersistRevMetadata.java:112)
    at wakiliproject.HomeController.showMetastring(HomeController.java:492)
    ... 40 more

通过示例查询，我只得到下面的输出，但没有数据。没有调用错误:

public void getAllEntityMetadataEg(int GUID) {
        RevMetadata m = new RevMetadata();
        m.setEntityGUID(GUID);
        Example e = Example.create(m);

        Criteria c = session.createCriteria(RevMetadata.class).add(e);
        for (Iterator it = c.list().iterator(); it.hasNext();) {
            RevMetadata item = (RevMetadata) it.next();
            System.out.println("-> All entity metadata for GUID: " + item.getName() + " : " + item.getValueId());
        }
}

输出:

Hibernate: select this_.id as id1_4_0_, this_.accessId as accessId2_4_0_, this_.entityGUID as entityGU3_4_0_, this_.name as name4_4_0_, this_.nameId as nameId5_4_0_, this_.ownerGUID as ownerGUI6_4_0_, this_.timeCreated as timeCrea7_4_0_, this_.valueId as valueId8_4_0_, this_.valueType as valueTyp9_4_0_ from METADATA this_ where (this_.accessId=? and this_.entityGUID=? and this_.nameId=? and this_.ownerGUID=? and this_.timeCreated=? and this_.valueId=?)

这些方法都不起作用。请帮助我使其工作，以便我可以获得包含 name 和 nameId

两个数据对象的列表

更新:

数据库表实体类:

public class RevMetadata implements Serializable {
    private String name;
    private int valueId;

}

Answer 1

如果只检索某些指定的列，结果将为List<Object[]> .

就您而言，Object[]将填充 name值 => 索引 0 和 nameId => 索引 1。需要将其转换为目标值的类型。

Criteria criteria = session.createCriteria(RevMetadata.class);
criteria.add(Restrictions.eq("entityGUID", GUID));

criteria.setProjection(Projections.projectionList()
                        .add(Projections.property("name"))
                        .add(Projections.property("nameId")));

List<Object[]> criteriaResult = criteria.list();

List<RevMetadata> results = new ArrayList<RevMetadata>();
//then get result into the class properties
for (Object[] object : criteriaResult) {
    //cast to target value type
    String name = (String)object[0];
    int nameId = ((Integer)object[1]).intValue();

    RevMetadata result = new RevMetadata();
    result.setName(name);
    result.setValueId(nameId);

    results.add(result);
}

//now results of List<RevMetadata> is ready