查询以空元素联接

Question

我在休眠状态下使用spring数据jpa。

@Entity
public class Samples {

    @EmbeddedId
    private SampleId id;

    @MapsId("samplingId")
    @ManyToOne(optional = false)
    private Samplings sampling;
    ..
}

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class Samplings {
    @OneToOne
    private Products product;

    @OneToOne
    private Dimensions dimension;

    @OneToOne
    private Colors color;
    ...
}

尺寸和颜色可以为空。

我搜索以samples，product，dimensions来获得colors（如果没有dimension，colors，也获得samples。

我做到了：

Join<Samples, Samplings> samplings = root.join("sampling", JoinType.INNER);
Join<Samples, Colors> colors = (Join) samplings.join("color", JoinType.INNER);
Join<Samples, Dimensions> dimension = (Join) samplings.join("dimension", JoinType.INNER);
Join<Samplings, Products> product = (Join) samplings.join("product", JoinType.INNER);

要获得结果，我需要为color和dimension放左？

Answer 1

  

如果没有尺寸，颜色，也想获取样品

要实现此目的，您需要将INNER JOIN和color上的dimension更改为LEFT JOIN s

Join<Samples, Samplings> samplings = root.join("sampling", JoinType.INNER);
Join<Samples, Colors> colors = (Join) samplings.join("color", JoinType.LEFT);
Join<Samples, Dimensions> dimension = (Join) samplings.join("dimension", JoinType.LEFT);
Join<Samplings, Products> product = (Join) samplings.join("product", JoinType.INNER);

根据您的用例，您可能还希望将INNER JOIN上的product转换为LEFT JOIN。