查询与null元素的加入

Question

我用弹簧数据的JPA与Hibernate。

@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;
    ...
}

尺寸和颜色可能为空。

我搜索得到samples与product，dimensions，colors（如果没有dimension，colors，希望得到samples太）。

我所做的：

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);

为了得到结果我需要我应该把留给color和dimension？

Answer 1

如果没有尺寸，颜色，想要得到的样本太

要做到这一点，你需要改变INNER JOIN和color到dimensions的LEFT JOINs：

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);

根据你的使用情况，您可能希望在INNER JOIN的product求助于LEFT JOIN为好。