复杂的休眠预测

Question

我想问一下，我创建的查询预测和标准是否有可能超过一层深度？ 我有 2 个模型类：

@Entity  
@Table(name = "person")  
public class Person implements Serializable {
    @Id
    @GeneratedValue
    private int personID;
    private double valueDouble;
    private int valueInt;
    private String name;
    @OneToOne(cascade = {CascadeType.ALL}, orphanRemoval = true)
    @JoinColumn(name="wifeId")
    private Wife wife;
       /*   
        *  Setter Getter    
        */
}


@Entity 
@Table(name = "wife")  
public class Wife implements Serializable {

    @Id
    @GeneratedValue     
    @Column(name="wifeId")
    private int id;
    @Column(name="name")
    private String name;
    @Column(name="age")
    private int age;            
    /*
     *  Setter Getter
     */       
}

我的标准 API：

ProjectionList projections = Projections.projectionList(); 
projections.add(Projections.property("this.personID"), "personID");
projections.add(Projections.property("this.wife"), "wife");
projections.add(Projections.property("this.wife.name"), "wife.name");

Criteria criteria = null; 
criteria = getHandlerSession().createCriteria(Person.class); 
criteria.createCriteria("wife", "wife", JoinType.LEFT.ordinal()); 
criterion = Restrictions.eq("wife.age", 19);  
criteria.add(criterion); 
criteria.setProjection(projections);
criteria.setResultTransformer(Transformers.aliasToBean(Person.class)); 
return criteria.list();

我希望，我可以查询 Person，具有指定的妻子财产条件，并指定返回结果集。 所以我使用 Projections 来获取指定的返回结果集

我想返回 personID、name(Person)、name(Wife)。我必须如何使用 API，我更喜欢使用 Hibernate Criteria API。

这一次，我使用上面的代码来获得我的预期结果，但它会抛出异常并显示错误消息： Exception in thread "main" org.hibernate.QueryException: could not resolve property: wife.name of: maladzan.model.Person, 以及我的Restrictions.eq("wife.age", 19); 是否适用于获取妻子年龄为 19 岁的人？

谢谢

Answer 1

AFAIK 无法使用 aliastobean 变压器投射超过一层的深度。您的选择是

• 创建平面数据传输对象 (DTO)
• 自己将生成的 Person 填充到内存中
• 实现您自己的结果转换器（类似于选项 2）

选项 1 如下所示：

Criteria criteria = getHandlerSession().createCriteria(Person.class)
    .createAlias("wife", "wife", JoinType.LEFT.ordinal())
    .add(Restrictions.eq("wife.age", 19)); 
    .setProjection(Projections.projectionList()
        .add(Projections.property("personID"), "personID")
        .add(Projections.property("name"), "personName")
        .add(Projections.property("wife.name"), "wifeName"));
    .setResultTransformer(Transformers.aliasToBean(PersonWifeDto.class));

return criteria.list();

Answer 2

我写了ResultTransformer，正是这样做的。它的名字是AliasToBeanNestedResultTransformer，查看github。

Answer 3

感谢萨米·安多尼。我能够使用您的 AliasToBeanNestedResultTransformer 稍作修改以适应我的情况。我发现嵌套转换器不支持字段位于超类中的场景，因此我对其进行了增强，以便在您要投影到的类的类继承层次结构中查找最多 10 级的字段：

    public Object transformTuple(Object[] tuple, String[] aliases) {

        ...


                if (alias.contains(".")) {
                    nestedAliases.add(alias);

                    String[] sp = alias.split("\\.");
                    String fieldName = sp[0];
                    String aliasName = sp[1];

                    Class<?> subclass = getDeclaredFieldForClassOrSuperClasses(resultClass, fieldName, 1);
...
}

其中getDeclaredFieldForClassOrSuperClasses()定义如下：

private Class<?> getDeclaredFieldForClassOrSuperClasses(Class<?> resultClass, String fieldName, int level) throws NoSuchFieldException{
    Class<?> result = null;
    try {
        result = resultClass.getDeclaredField(fieldName).getType();
    } catch (NoSuchFieldException e) {
        if (level <= 10){
        return getDeclaredFieldForClassOrSuperClasses(
                resultClass.getSuperclass(), fieldName, level++);
        } else {
            throw e;
        }
    }
    return result;
}

我对这个嵌套属性的 Hibernate 投影如下所示：

Projections.projectionList().add( Property.forName("metadata.copyright").as("productMetadata.copyright"));

我要投影的课程如下所示：

public class ProductMetadata extends AbstractMetadata {
...
}

public abstract class AbstractMetadata {
...   
   protected String copyright;
...
}

Answer 4

而不是创建Data Transfer Object (DTO)
在projectionlist 中进行以下更改，它将对您有用。

    ProjectionList projections = Projections.projectionList(); 
    projections.add(Projections.property("person.personID"), "personID");
    projections.add(Projections.property("person.wife"), "wife");
    projections.add(Projections.property("wife.name"));

    Criteria criteria = null; 
    criteria = getHandlerSession().createCriteria(Person.class,"person").createAlias("person.wife", "wife"); 
    criterion = Restrictions.eq("wife.age", 19);  
    criteria.add(criterion); 
    criteria.setProjection(projections);
    criteria.setResultTransformer(Transformers.aliasToBean(Person.class)); 
    return criteria.list();