jpa api原生JOIN-基於CriteriaQuery的關聯

EntityManager em = emf.createEntityManager();
CriteriaBuilder cb = em.getCriteriaBuilder();

CriteriaQuery<TestStudentPo> query = cb.createQuery(TestStudentPo.class);

Root<TestStudentPo> root = query.from(TestStudentPo.class);
//建立關聯關係
Join<TestStudentPo, TestClassPo> join = root.join("testClassPo", JoinType.LEFT);

query.select(root).where(cb.equal(join.get("classId"), "1"));

List<TestStudentPo> list = em.createQuery(query).getResultList();

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這段JPA API 轉爲sql爲：

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SELECT
a.STUDENT_ID AS STUDENT_1_2_,
a.CLASS_ID AS CLASS_ID2_2_,
a.COURSE_ID AS COURSE_I3_2_,
a.STUDENT_NAME AS STUDENT_4_2_,
a.TIME AS TIME5_2_
FROM
test_student a
LEFT OUTER JOIN test_class b ON a.CLASS_ID = b.CLASS_ID
WHERE
b.CLASS_ID =?

最重要的是這個關係要配置好

@OneToOne
    @JoinColumn(name="CLASS_ID",referencedColumnName = "CLASS_ID")
    private TestClassPo testClassPo;