在多列联接表上使用投影

Question

日安。

因此，我有mapping@id@generatedvalue（strategy=generationtype.sequence,generator=“discount_fares_id_sequence”）@sequenceGenerator（name=“discount_fares_id_sequence”,sequenceName=“discount_fares_id_seq”,allocationSize=1）私有长ID；

@Column
private Long discount;

@Column(name = "fare_code", length = 255)
private String fareCode;

@ManyToOne
@JoinColumn(name = "aircompany_id", foreignKey = @ForeignKey(name = "fk_discfares_ref_aircompany_id"))
private AircompanyRB aircompanyId;

我如何使用投影只提取

discountFare id discountfarecode和aircompany_id（AircompanyRB的密钥）

所以基本上所有的DiscountFares字段加上AirCompanyRB的唯一关键字？

我试过了

    DetachedCriteria criteria = DetachedCriteria.forClass(DiscountFares.class)
        .createCriteria("aircompanyId")
        .setProjection(Projections.projectionList()
        .add(Projections.property("id"))
        .add(Projections.property("discount"))
        .add(Projections.property("fareCode")));

    List<DiscountFares> result = criteria.getExecutableCriteria(sessionFactory.getCurrentSession()).list();

但它会抛出异常，表示AircompanyRB没有字段“DiscountFares”（是的，它没有-DiscountFares有）

非常感谢！我们非常感谢任何帮助

Answer 1

首先,使用条件查询而不是死气沉沉的简单HQL查询会使您的生活变得困难：

select df.id, df.discount, df.fareCode, ac.id 
from DiscountFares df
left join df.aircompanyId ac

现在，如果您真的想使用一个条件，只需翻译上面的查询：

Criteria c = session.createCriteria(DiscountFares.class, "df");
c.createAlias("df.aircompanyId", "ac", JoinType.LEFT_OUTER_JOIN);
c.setProjection(Projections.projectionList()
    .add(Projections.property("df.id"))
    .add(Projections.property("df.discount"))
    .add(Projections.property("df.fareCode"))
    .add(Projections.property("ac.id")));