CriteriaBuilder：使用ON子句一对多连接 [英] CriteriaBuilder: join one-to-many with ON clause

问题描述

假设您具有以下一对多关系：学校->学生-> ScientificWork 。现在，您要选择所有学生名为 John且其科学工作称为 Black Holes的学校。

Suppose you the following OneToMany relationships: School->Student->ScientificWork. Now you want to select all Schools that have Student with name 'John' and his scientific job is called 'Black Holes'.

我这样做如下，但是由于某种原因，它使我所有可能的学校都退学了。

I do it like the following, but for some reason it retrurns me all possible schools.

public static Specification<School> spec() {
    return (root, query, cb) -> {
        final SetJoin<School, Student> studs = root.joinSet("students", JoinType.LEFT);
        final SetJoin<Student, ScientificWork> works = root.joinSet("works", JoinType.LEFT);
        return cb.and(
                cb.equal(studs.get(Student_.name), 'John'),
                cb.equal(nodes.get(ScientificWork_.name), 'Black Holes')
        );
    };
}

更新

找到此答案我尝试了以下操作，但结果相同（返回的是所有学校而不是一个学校）：

Update

After finding this answer I tried the following, but with the same result (it returns me all Schools instead of one):

public static Specification<School> spec() {
    return (root, query, cb) -> {
        final SetJoin<School, Student> studs = root.joinSet("students", JoinType.LEFT);
        studs.on(cb.equal(studs.get(Student_.name), 'John'));
        final SetJoin<Student, ScientificWork> works = root.joinSet("works", JoinType.LEFT);          
        return cb.equal(nodes.get(ScientificWork_.name), 'Black Holes');
    };
}

推荐答案

public static Specification<School> spec() {
return (root, query, cb) -> {
    final Join<School, Student> studs = root.join("students", JoinType.LEFT);
    studs.on(cb.equal(studs.get(Student_.name), "John"));
    final Join<Student, ScientificWork> works = studs.join("works", JoinType.LEFT);          
    return cb.equal(works.get(ScientificWork_.name), "Black Holes");
};

}

我使用了加入而不是 joinSet ，然后将 ** works **。get（ScientificWork_.name）代替 ** nodes **。get（ScientificWork_.name）

I used join instead of joinSet and put **works**.get(ScientificWork_.name) instead of **nodes**.get(ScientificWork_.name)

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