Hibernate5入门（五）查询方式之QBC

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参考地址：https://mp.csdn.net/postedit

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目录

一、QBC检索方式

1.1 查询全部

1.2 通过条件查询

1.2.1 and

1.2.2 or

1.2.3 like

1.2.4 in

1.2.5 Restrictions的条件取值

1.3 连接查询

1.4 分页查询

1.5 排序

1.6 统计

1.7 聚合函数

1.8 多列查询

1.9 非空查询

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一、QBC检索方式

QBC:Query By Criteria,是一种更加面向对象的查询语言，提供的一系列QBC API来检索对象。

HQL所能做的事情，使用QBC也大多能做用，这个通过实例来看看QBC是如何使用的。

有些方法已经弃用，代替方法还没有总结。

1.1 查询全部

	@Test
	void testGetAll() {
		// 创建criteriaQuery对象
		Criteria criteria = session.createCriteria(Employee.class);
		// 获取结果集
		List employees = criteria.list();
		System.out.println(employees);
	}

Hibernate: 
SELECT
    employee0_.empId AS empId1_1_,
    employee0_.empName AS empName2_1_,
    employee0_.deptId AS deptId3_1_ 
FROM
    t_employee employee0_

 结果集是对象组成的数组：
[demo.entity.Employee@37d871c2, 
demo.entity.Employee@7a904f32, 
demo.entity.Employee@2b59501e, 
demo.entity.Employee@476e8796]

1.2 通过条件查询

1.2.1 and

	// 多条件and
	@Test
	void testGetByConditionAnd() {
		// 创建criteriaQuery对象
		Criteria criteria = session.createCriteria(Employee.class);
		// add添加条件，通过Restrictions(字段名，值)eq是等于，默认是and
		List employees = criteria.add(Restrictions.eq("empId", 1)).add(Restrictions.eq("empName", "员工1"))
				.list();
		System.out.println(employees);
	}

Hibernate SQL: 
SELECT
    this_.empId AS empId1_1_,
    this_.empName AS empName2_1_,
    this_.deptId AS deptId3_1_ 
FROM
    t_employee this_
WHERE
     this_.empId=? and this_.empName=?

结果集一个员工对象：
[demo.entity.Employee@21ac5eb4]

1.2.2 or

	// 多条件or
	@Test
	void testGetByConditionOr() {
		// 创建criteriaQuery对象
		Criteria criteria = session.createCriteria(Employee.class);
		// 多条件or
		List employees = criteria
				.add(Restrictions.or(Restrictions.eq("empId", 1), Restrictions.like("empName", "员工1%").ignoreCase()))
				.list();
		System.out.println(employees);
	}

Hibernate SQL: 
SELECT
    this_.empId AS empId1_1_,
    this_.empName AS empName2_1_,
    this_.deptId AS deptId3_1_ 
FROM
    t_employee this_
WHERE
     (this_.empId=? or lower(this_.empName) like ?)

结果集一个员工对象：
[demo.entity.Employee@21ac5eb4]

1.2.3 like

	@Test
	void testGetByConditionLike() {
		// 创建criteriaQuery对象
		Criteria criteria = session.createCriteria(Employee.class);
		// like查询，俩种写法
		// List employees = criteria.add(Restrictions.like("empName", "员工1%").ignoreCase()).list();
		List employees = criteria.add(Restrictions.like("empName", "员工1", MatchMode.ANYWHERE).ignoreCase()).list();
		System.out.println(employees);
	}

 

Hibernate SQL: 
SELECT
    this_.empId AS empId1_1_,
    this_.empName AS empName2_1_,
    this_.deptId AS deptId3_1_ 
FROM
    t_employee this_
WHERE
     lower(this_.empName) like ?

结果集一个员工对象：
[demo.entity.Employee@21ac5eb4]

1.2.4 in

	@Test
	void testGetByConditionIn() {
		// 创建criteriaQuery对象
		Criteria criteria = session.createCriteria(Employee.class);
		List employees = criteria.add(Restrictions.in("empId", new Integer[]{1, 2})).list();
		System.out.println(employees);
	}

Hibernate SQL: 
SELECT
    this_.empId AS empId1_1_,
    this_.empName AS empName2_1_,
    this_.deptId AS deptId3_1_ 
FROM
    t_employee this_
WHERE
    this_.empId in (?, ?)

结果集一个员工对象：
[demo.entity.Employee@21ac5eb4]

1.2.5 Restrictions的条件取值

实现数据库sql的条件查询

Restrictions的条件取值

Restrictions.eq	等于
Restrictions.allEq	多个等于判断（多个key/value）
Restrictions.gt	大于
Restrictions.ge	大于等于
Restrictions.lt	小于
Restrictions.le	小于等于
Restrictions.between	对应sql的between
Restrictions.like	对应sql的like
Restrictions.in	对应sql的in
Restrictions.and	and
Restrictions.or	or
Restrictions.sqlRestriction	sql限定查询
Restrictions.asc()	升序
Restrictions.desc()	降序
Restrictions.isNotNull	非空查询

1.3 连接查询

	@Test
	void testGetInnerJoin() {
		// 创建criteriaQuery对象
		Criteria criteria = session.createCriteria(Employee.class);
		// createAlias默认是内连接，可以不用写。可以为dept表取别名，也可以不取
		criteria.createAlias("dept", "d", Criteria.LEFT_JOIN);
		List employees = criteria.list();
		System.out.println(employees);
	}

Hibernate: 
SELECT
    this_.empId AS empId1_1_0_,
    dept1_.deptId AS deptId1_0_1_,
    this_.empName AS empName2_1_0_,
    this_.deptId AS deptId3_1_0_,
    dept1_.deptName AS deptName2_0_1_ 
FROM
    t_employee this_
    left outer join t_dept d1_ on this_.deptId=d1_.deptId

结果集是以这种方式
[demo.entity.Employee@3b2f4a93, 
demo.entity.Employee@213bd3d5, 
demo.entity.Employee@451882b2, 
demo.entity.Employee@4a23350]

1.4 分页查询

	@Test
	void testGetLimit() {
		// 创建criteriaQuery对象
		Criteria criteria = session.createCriteria(Employee.class);
		// 从第1条开始取2条
		List employees = criteria.setFirstResult(1).setMaxResults(2).list();
		System.out.println(employees);
	}

Hibernate: 
SELECT
    this_.empId AS empId1_1_,
    this_.empName AS empName2_1_,
    this_.deptId AS deptId3_1_ 
FROM
    t_employee this_
    LIMIT ?,    ?

结果集是Employee对象数组： 
[demo.entity.Employee@4acb2510, demo.entity.Employee@4e1459ea]

1.5 排序

	@Test
	void testOrder() {
		// 创建criteriaQuery对象
		Criteria criteria = session.createCriteria(Employee.class);
		// empId排序
		List employees = criteria.addOrder(Order.desc("empId")).list();
		System.out.println(employees);
	}

Hibernate: 
SELECT
     this_.empId AS empId1_1_,
     this_.empName AS empName2_1_,
     this_.deptId AS deptId3_1_ 
FROM
    t_employee this_
    order by this_.empId desc

结果集是Employee对象数组： 
[demo.entity.Employee@4acb2510, demo.entity.Employee@4e1459ea]

1.6 统计

查部门下的员工数

	@Test
	public void testCount() {
		Criteria criteria = session.createCriteria(Employee.class);
		// 统计部门1下的员工
		List employees = criteria.setProjection(Projections.rowCount()).add(Restrictions.eq("dept.deptId", 1)).list();
		System.out.println(employees);
	}

Hibernate: 
SELECT
    count(*) as y0_ 
FROM
    t_employee this_

WHERE
    this_.deptId=?

结果集是Employee对象数组： 
[2]

1.7 聚合函数

查部门下的员工数

	@Test
	public void testFunc() {
		Criteria criteria = session.createCriteria(Employee.class);
		// 统计部门1下的员工
		List employees = criteria.setProjection(Projections.projectionList()
                .add(Projections.property("dept.deptId"))
                .add(Projections.rowCount())
                .add(Projections.avg("empId"))
                .add(Projections.max("empId"))
                .add(Projections.min("empId"))
                .add(Projections.sum("empId"))
                .add(Projections.groupProperty("dept.deptId"))
        ).list();
		System.out.println(employees);
	}

Hibernate: 
SELECT
    this_.deptId AS y0_,
    count( * ) AS y1_,
    avg( this_.empId ) AS y2_,
    max( this_.empId ) AS y3_,
    min( this_.empId ) AS y4_,
    sum( this_.empId ) AS y5_,
    this_.deptId AS y6_ 
FROM
    t_employee this_ 
GROUP BY
    this_.deptId

结果集是Employee对象数组： 
[[Ljava.lang.Object;@38b5f25, [Ljava.lang.Object;@327ed9f5]

1.8 多列查询

	@Test
	public void testCount() {
		Criteria criteria = session.createCriteria(Employee.class);
		// 统计部门1下的员工
		List employees = criteria.setProjection(Projections.rowCount()).add(Restrictions.eq("dept.deptId", 1)).list();
		System.out.println(employees);
	}

Hibernate: 
SELECT
   this_.empId AS empId1_1_,
   this_.empName AS empName2_1_,
FROM
    t_employee this_

结果集是Employee对象数组：
[[Ljava.lang.Object;@2776015d, 
[Ljava.lang.Object;@b174a73, 
[Ljava.lang.Object;@2e3f79a2, 
[Ljava.lang.Object;@1460c81d]

1.9 非空查询

	@Test
	public void testNotNull() {
		Criteria criteria = session.createCriteria(Employee.class);
		// 统计部门1下的员工
		List employees = criteria.add(Restrictions.isNotNull("empId")).list();
		System.out.println(employees);
	}

Hibernate: 
SELECT
    this_.empId AS empId1_1_,
    this_.empName AS empName2_1_,
    this_.deptId AS deptId3_1_ 
FROM
    t_employee this1_
WHERE
    this_.empId is not null

结果集是Employee对象数组： 
[demo.entity.Employee@4acb2510, demo.entity.Employee@4e1459ea]