JPA(Java Persistence API)学习十六（标准API介绍）

1.概述

    标准(Criteria)API是构建实体及其持久状态查询的最常用方法之一。

   它只是定义JPA查询的另一种方法。Criteria API定义了一个独立于平台的条件查询，

   用Java编程语言编写。 它是在JPA 2.0中引入的。 这背后的主要目的是提供一种类型安全的方式来表达查询。

2.创建条件查询的步骤

   第一步： 通过在EntityManager接口实例上调用getCriteriaBuilder()方法创建CriteriaBuilder接口的对象。

         EntityManager em = emf.createEntityManager(); 

         CriteriaBuilder cb=em.getCriteriaBuilder();

   第二步：构建一个CriteriaQuery接口的实例来创建一个查询对象。

         CriteriaQuery<StudentEntity> cq=cb.createQuery(StudentEntity.class);

 

   第三步：从CriteriaQuery对象的方法调用来设置查询根。

         Root<StudentEntity> stud=cq.from(StudentEntity.class);

 

   第四步：调用CriteriaQuery对象的select()方法来指定查询结果的类型。

         CriteriaQuery<StudentEntity> select = cq.select(stud);

 

    第五步：创建Query接口的实例并指定用于访问数据库记录的方法的类型。

         Query q = em.createQuery(select);

 

   第六步：通过调用查询接口的方法来控制查询的执行。

        List<StudentEntity> list = q.getResultList();

 

3.标准API查询子句的方法（以下是相应接口和方法的子句列表）

子句	Criteria API接口	方法
SELECT	CriteriaQuery	select()
FROM	AbstractQuery	from()
WHERE	AbstractQuery	where()
ORDER BY	CriteriaQuery	orderBy()
GROUP BY	AbstractQuery	groupBy()
HAVING	AbstractQuery	having()

   

注意: CriteriaQuery接口是AbstractQuery接口的子接口。

 

4.标准的select查询

     EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

    EntityManager em = emf.createEntityManager();
    em.getTransaction().begin();
    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<StudentEntity> cq = cb.createQuery(StudentEntity.class);

 

    Root<StudentEntity> stud = cq.from(StudentEntity.class);

 

    cq.select(stud.get("s_name"));

 

    CriteriaQuery<StudentEntity> select = cq.select(stud);
    TypedQuery<StudentEntity> q = em.createQuery(select);
    List<StudentEntity> list = q.getResultList();

 

    System.out.println("s_id");

 

    for (StudentEntity s : list) {
        System.out.println(s.getS_id());

 

    }

 

    em.getTransaction().commit();
    em.close();
    emf.close();

 

 

5.选择多个表达式（查询）

     EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

    EntityManager em = emf.createEntityManager();
    em.getTransaction().begin();
    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<StudentEntity> cq = cb.createQuery(StudentEntity.class);

    Root<StudentEntity> stud = cq.from(StudentEntity.class);

    cq.multiselect(stud.get("s_id"), stud.get("s_name"), stud.get("s_age"));
    CriteriaQuery<StudentEntity> select = cq.select(stud);
    TypedQuery<StudentEntity> q = em.createQuery(select);
    List<StudentEntity> list = q.getResultList();

    System.out.print("s_id");
    System.out.print("\t s_name");
    System.out.println("\t s_age");

    for (StudentEntity s : list) {
        System.out.print(s.getS_id());
        System.out.print("\t" + s.getS_name());
        System.out.println("\t" + s.getS_age());
    }

    em.getTransaction().commit();
    em.close();
    emf.close();

 

6.标准ORDER BY示例

    EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

    EntityManager em = emf.createEntityManager();
    em.getTransaction().begin();
    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<StudentEntity> cq = cb.createQuery(StudentEntity.class);

    Root<StudentEntity> stud = cq.from(StudentEntity.class);

    cq.orderBy(cb.asc(stud.get("s_age")));//升序排序

    //cq.orderBy(cb.desc(stud.get("s_age")));  //降序排序
    CriteriaQuery<StudentEntity> select = cq.select(stud);
    TypedQuery<StudentEntity> q = em.createQuery(select);
    List<StudentEntity> list = q.getResultList();

    System.out.print("s_id");
    System.out.print("\t s_name");
    System.out.println("\t s_age");

    for (StudentEntity s : list) {
        System.out.print(s.getS_id());
        System.out.print("\t" + s.getS_name());
        System.out.println("\t" + s.getS_age());
    }

    em.getTransaction().commit();
    em.close();
    emf.close();

 

7.标准WHERE示例

    EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

    EntityManager em = emf.createEntityManager();
    em.getTransaction().begin();

    CriteriaBuilder cb = em.getCriteriaBuilder();

    AbstractQuery<StudentEntity> cq1 = cb.createQuery(StudentEntity.class);
    AbstractQuery<StudentEntity> cq2 = cb.createQuery(StudentEntity.class);

    Root<StudentEntity> stud1 = cq1.from(StudentEntity.class);

    cq1.where(cb.greaterThan(stud1.get("s_age"), 22));//greaterThan大于

    CriteriaQuery<StudentEntity> select1 = ((CriteriaQuery<StudentEntity>) cq1).select(stud1);
    TypedQuery<StudentEntity> tq1 = em.createQuery(select1);
    List<StudentEntity> list1 = tq1.getResultList();

    System.out.println("Students having age greater than 22");

    System.out.print("s_id");
    System.out.print("\t s_name");
    System.out.println("\t s_age");

    for (StudentEntity s : list1) {
        System.out.print(s.getS_id());
        System.out.print("\t" + s.getS_name());
        System.out.println("\t" + s.getS_age());
    }

    Root<StudentEntity> stud2 = cq2.from(StudentEntity.class);

    cq2.where(cb.lessThan(stud2.get("s_age"), 22));//lessThan小于

    CriteriaQuery<StudentEntity> select2 = ((CriteriaQuery<StudentEntity>) cq2).select(stud2);
    TypedQuery<StudentEntity> tq2 = em.createQuery(select2);
    List<StudentEntity> list2 = tq2.getResultList();

    System.out.println("Students having age Less than 22");

    System.out.print("s_id");
    System.out.print("\t s_name");
    System.out.println("\t s_age");

    for (StudentEntity s : list2) {
        System.out.print(s.getS_id());
        System.out.print("\t" + s.getS_name());
        System.out.println("\t" + s.getS_age());
    }

    em.getTransaction().commit();
    em.close();
    emf.close();

 

8.JPQL Between条件

     EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

    EntityManager em = emf.createEntityManager();
    em.getTransaction().begin();

    CriteriaBuilder cb = em.getCriteriaBuilder();

    AbstractQuery<StudentEntity> cq = cb.createQuery(StudentEntity.class);

    Root<StudentEntity> stud = cq.from(StudentEntity.class);

    cq.where(cb.between(stud.get("s_age"), 22, 26));
    CriteriaQuery<StudentEntity> select = ((CriteriaQuery<StudentEntity>) cq).select(stud);
    TypedQuery<StudentEntity> tq = em.createQuery(select);
    List<StudentEntity> list = tq.getResultList();

    System.out.println("Students having age between 22 and 26");

    System.out.print("s_id");
    System.out.print("\t s_name");
    System.out.println("\t s_age");

    for (StudentEntity s : list) {
        System.out.print(s.getS_id());
        System.out.print("\t" + s.getS_name());
        System.out.println("\t" + s.getS_age());
    }

    em.getTransaction().commit();
    em.close();
    emf.close();

 

9.JPQL Like条件

    EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

    EntityManager em = emf.createEntityManager();
    em.getTransaction().begin();

    CriteriaBuilder cb = em.getCriteriaBuilder();

    AbstractQuery<StudentEntity> cq = cb.createQuery(StudentEntity.class);

    Root<StudentEntity> stud = cq.from(StudentEntity.class);

    cq.where(cb.like(stud.get("s_name"), "R%"));
    CriteriaQuery<StudentEntity> select = ((CriteriaQuery<StudentEntity>) cq).select(stud);
    TypedQuery<StudentEntity> tq = em.createQuery(select);
    List<StudentEntity> list = tq.getResultList();

    System.out.println("Students name starting with R");

    System.out.print("s_id");
    System.out.print("\t s_name");
    System.out.println("\t s_age");

    for (StudentEntity s : list) {
        System.out.print(s.getS_id());
        System.out.print("\t" + s.getS_name());
        System.out.println("\t" + s.getS_age());
    }
    em.getTransaction().commit();
    em.close();
    emf.close();

 

10.JPQL In条件

     EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

    EntityManager em = emf.createEntityManager();
    em.getTransaction().begin();

    CriteriaBuilder cb = em.getCriteriaBuilder();

    AbstractQuery<StudentEntity> cq = cb.createQuery(StudentEntity.class);

    Root<StudentEntity> stud = cq.from(StudentEntity.class);

    cq.where(cb.in(stud.get("s_age")).value(22).value(24));
    CriteriaQuery<StudentEntity> select = ((CriteriaQuery<StudentEntity>) cq).select(stud);
    TypedQuery<StudentEntity> tq = em.createQuery(select);
    List<StudentEntity> list = tq.getResultList();

    System.out.println("Students having age 22 and 24");

    System.out.print("s_id");
    System.out.print("\t s_name");
    System.out.println("\t s_age");

    for (StudentEntity s : list) {
        System.out.print(s.getS_id());
        System.out.print("\t" + s.getS_name());
        System.out.println("\t" + s.getS_age());
    }

    em.getTransaction().commit();
    em.close();
    emf.close();

 

11.标准GROUP BY示例

     EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

    EntityManager em = emf.createEntityManager();
    em.getTransaction().begin();

    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<Object[]> cq = cb.createQuery(Object[].class);
    Root<StudentEntity> stud = cq.from(StudentEntity.class);
    cq.multiselect(stud.get("s_age"), cb.count(stud)).groupBy(stud.get("s_age"));

    System.out.print("s_age");
    System.out.println("\t Count");
    List<Object[]> list = em.createQuery(cq).getResultList();
    for (Object[] object : list) {
        System.out.println(object[0] + "     " + object[1]);

    }

    em.getTransaction().commit();
    em.close();
    emf.close();

 

12.标准Having示例

     EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

    EntityManager em = emf.createEntityManager();
    em.getTransaction().begin();

    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<Object[]> cq = cb.createQuery(Object[].class);
    Root<StudentEntity> stud = cq.from(StudentEntity.class);

    cq.multiselect(stud.get("s_age"), cb.count(stud)).groupBy(stud.get("s_age"))
            .having(cb.ge(stud.get("s_age"), 24));

    System.out.print("s_age");
    System.out.println("\t Count");
    List<Object[]> list = em.createQuery(cq).getResultList();
    for (Object[] object : list) {
        System.out.println(object[0] + " " + object[1]);

    }

    em.getTransaction().commit();
    em.close();
    emf.close();

 

 

学习来源：https://www.yiibai.com/jpa/jpa-criteria-api-introduction.html#article-start