Hibernate - QBC和本地SQL对象检索详解

【1】QBC检索

QBC 查询就是通过使用 Hibernate 提供的 Query By Criteria API 来查询对象，这种 API 封装了 SQL 语句的动态拼装，对查询提供了更加面向对象的功能接口。即使用面向对象的思想实现动态SQL拼接一样的功能，可以理解一下HQL和标准SQL。

这里就需要了解几个接口和实现类。

① Criterion接口

An object-oriented representation of a query criterion that may be used as a restriction in a Criteria query.

查询准则的面向对象表示，可作为Criteria 查询中的规则。

Built-in criterion types are provided by the Restrictions factory class. This interface might be implemented by application classes that define custom restriction criteria.

内置的标准类型由Restrictions 工厂类提供。此接口可以由定义自定义约束标准的应用程序类实现。

其源码如下：

public interface Criterion extends Serializable {

	/**
	 * Render the SQL fragment
	 *
	 * @param criteria The local criteria
	 * @param criteriaQuery The overal criteria query
	 *
	 * @return The generated SQL fragment
	 * @throws org.hibernate.HibernateException Problem during rendering.
	 */
	public String toSqlString(Criteria criteria, CriteriaQuery criteriaQuery) throws HibernateException;
	
	/**
	 * Return typed values for all parameters in the rendered SQL fragment
	 *
	 * @param criteria The local criteria
	 * @param criteriaQuery The overal criteria query
	 *
	 * @return The types values (for binding)
	 * @throws HibernateException Problem determining types.
	 */
	public TypedValue[] getTypedValues(Criteria criteria, CriteriaQuery criteriaQuery) throws HibernateException;

}

其实现类如下图所示：

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② Restrictions类

该类主要产生Criterion对象，Criteria 通过组合一系列的Criterion对象来检索实体。

方法如下图所示：

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③ Criteria接口

继承自CriteriaSpecification，Criteria实现类为CriteriaImpl，Criteria的javadoc如下：

功能说明：Criteria是一个检索entities的简单API，通过组合Criterion对象实现检索功能
Criteria is a simplified API for retrieving entities
 * by composing Criterion objects. This is a very
 * convenient approach for functionality like "search" screens
 * where there is a variable number of conditions to be placed
 * upon the result set.

 * 

 * The Session is a factory for Criteria.
 * Criterion instances are usually obtained via
 * the factory methods on Restrictions. eg.
 * 
 * List cats = session.createCriteria(Cat.class)
 *     .add( Restrictions.like("name", "Iz%") )
 *     .add( Restrictions.gt( "weight", new Float(minWeight) ) )
 *     .addOrder( Order.asc("age") )
 *     .list();
 * 
 * 导航对象图检索方式
 * You may navigate associations using createAlias() or
 * createCriteria().
 * 
 * List cats = session.createCriteria(Cat.class)
 *     .createCriteria("kittens")
 *         .add( Restrictions.like("name", "Iz%") )
 *     .list();
 * 
 * 
 * List cats = session.createCriteria(Cat.class)
 *     .createAlias("kittens", "kit")
 *     .add( Restrictions.like("kit.name", "Iz%") )
 *     .list();
 * 
 * 报表查询--聚集函数
 * You may specify projection and aggregation using Projection
 * instances obtained via the factory methods on Projections.
 * 
 * List cats = session.createCriteria(Cat.class)
 *     .setProjection( Projections.projectionList()
 *         .add( Projections.rowCount() )
 *         .add( Projections.avg("weight") )
 *         .add( Projections.max("weight") )
 *         .add( Projections.min("weight") )
 *         .add( Projections.groupProperty("color") )
 *     )
 *     .addOrder( Order.asc("color") )
 *     .list();
 * 

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④ Projections

一系列聚集函数的工厂类，用来产生Projection(An object-oriented representation of a query result set projection in a Criteria query.)对象，其方法如下图所示：

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【2】代码测试

① 普通查询

测试代码如下：

	@Test
	public void testQBC(){
		//1. 创建一个 Criteria 对象
		Criteria criteria = session.createCriteria(Employee.class);
		
		//2. 添加查询条件: 在 QBC 中查询条件使用 Criterion 来表示
		//Criterion 可以通过 Restrictions 的静态方法得到
		criteria.add(Restrictions.eq("email", "[email protected]"));
		criteria.add(Restrictions.gt("salary", 500F));
		
		//3. 执行查询
		Employee employee = (Employee) criteria.uniqueResult();
		System.out.println(employee); 
	}

测试结果如下：

Hibernate: 
    select
        this_.ID as ID1_1_0_,
        this_.NAME as NAME2_1_0_,
        this_.SALARY as SALARY3_1_0_,
        this_.EMAIL as EMAIL4_1_0_,
        this_.DEPT_ID as DEPT_ID5_1_0_ 
    from
        GG_EMPLOYEE this_ 
    where
        this_.EMAIL=? 
        and this_.SALARY>?
Employee [id=1]

上面这种方式与普通HQL查询是等价的。

String HQL = "FROM Employee e where e.email = :email and e.salary > :salary";

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② And 和Or查询

And使用Conjunction表示，Or使用Disjunction表示，其均是Junction子类。

测试代码如下：

	@Test
	public void testQBC2(){
		Criteria criteria = session.createCriteria(Employee.class);
		
		//1. AND: 使用 Conjunction 表示
		//Conjunction 本身就是一个 Criterion 对象
		//且其中还可以添加 Criterion 对象
		Conjunction conjunction = Restrictions.conjunction();
		conjunction.add(Restrictions.like("name", "A", MatchMode.ANYWHERE));
		Department dept = new Department();
		dept.setId(1);
		conjunction.add(Restrictions.eq("dept", dept));
		System.out.println(conjunction); 
		
		//2. OR
		Disjunction disjunction = Restrictions.disjunction();
		disjunction.add(Restrictions.ge("salary", 3000F));
		disjunction.add(Restrictions.isNull("email"));
		
		System.out.println(disjunction);
		
		criteria.add(disjunction);
		criteria.add(conjunction);
		
		List list = criteria.list();
		for(Employee employee:list){
			System.out.println(employee);
		}
	}

测试结果如下：

(name like %A% and dept=Department [id=1])
(salary>=3000.0 or email is null)
Hibernate: 
    select
        this_.ID as ID1_1_0_,
        this_.NAME as NAME2_1_0_,
        this_.SALARY as SALARY3_1_0_,
        this_.EMAIL as EMAIL4_1_0_,
        this_.DEPT_ID as DEPT_ID5_1_0_ 
    from
        GG_EMPLOYEE this_ 
    where
        (
            this_.SALARY>=? 
            or this_.EMAIL is null
        ) 
        and (
            this_.NAME like ? 
            and this_.DEPT_ID=?
        )
Employee [id=1]

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③ 对象导航检索测试

测试代码如下：

	@Test
	public void testQBC1(){
		 List list = session.createCriteria(Employee.class).
//				 createCriteria("dept","d")
//				 .add( Restrictions.like("d.name", "%A%") )
				 createCriteria("dept")
				 .add( Restrictions.like("name", "%A%") )
				 .list();
		 for(Employee employee:list){
				System.out.println(employee);
			}
	}

测试结果如下：

Hibernate: 
    select
        this_.ID as ID1_1_1_,
        this_.NAME as NAME2_1_1_,
        this_.SALARY as SALARY3_1_1_,
        this_.EMAIL as EMAIL4_1_1_,
        this_.DEPT_ID as DEPT_ID5_1_1_,
        department1_.ID as ID1_0_0_,
        department1_.NAME as NAME2_0_0_ 
    from
        GG_EMPLOYEE this_ 
    inner join
        GG_DEPARTMENT department1_ 
            on this_.DEPT_ID=department1_.ID 
    where
        department1_.NAME like ?
Employee [id=1]
Employee [id=2]

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④ 聚集函数测试

测试代码如下：

	@Test
	public void testQBC3(){
		Criteria criteria = session.createCriteria(Employee.class);
		
		//统计查询: 使用 Projection 来表示: 可以由 Projections 的静态方法得到
		criteria.setProjection(Projections.max("salary"));
		
		System.out.println(criteria.uniqueResult()); 
	}

测试结果如下：

Hibernate: 
    select
        max(this_.SALARY) as y0_ 
    from
        GG_EMPLOYEE this_
10000.0

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⑤ 分页和排序

测试代码如下：

	@Test
	public void testQBC4(){
		Criteria criteria = session.createCriteria(Employee.class);
		
		//1. 添加排序
		criteria.addOrder(Order.asc("salary"));
		criteria.addOrder(Order.desc("email"));
		
		//2. 添加翻页方法
		int pageSize = 2;
		int pageNo = 2;
		List list = criteria.setFirstResult((pageNo - 1) * pageSize)
		        .setMaxResults(pageSize)
		        .list();
		for(Employee employee:list){
			System.out.println(employee);
		}
	}

测试结果如下：

Hibernate: 
    select
        this_.ID as ID1_1_0_,
        this_.NAME as NAME2_1_0_,
        this_.SALARY as SALARY3_1_0_,
        this_.EMAIL as EMAIL4_1_0_,
        this_.DEPT_ID as DEPT_ID5_1_0_ 
    from
        GG_EMPLOYEE this_ 
    order by
        this_.SALARY asc,
        this_.EMAIL desc limit ?,
        ?
Employee [id=8]
Employee [id=2]

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【3】本地SQL查询

本地SQL查询来完善HQL不能涵盖所有的查询特性，这里主要使用createSQLQuery或createNativeQuery来创建NativeQuery 对象。二者有所区别的是前者创建的query对象在设置参数时索引从0开始，后者从1开始。

测试代码如下：

	@Test
	public void testNativeSQL(){
		String sql = "INSERT INTO gg_department VALUES(?, ?)";
		Query query = session.createSQLQuery(sql);
		int executeUpdate = query.setInteger(0, 15).setString(1, "JANE").executeUpdate();
//		NativeQuery query = session.createNativeQuery(sql);
//		int executeUpdate = query.setInteger(1, 15).setString(2, "JANE").executeUpdate();
		
		System.out.println(executeUpdate);
	}

测试结果如下：

Hibernate: 
    INSERT 
    INTO
        gg_department
        
    VALUES
        (?, ?)
1

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【4】HQL的更新和删除操作

前面所讲的HQL均是各种查询操作，同样HQL也支持更新和删除(但是不支持插入操作)。

测试代码如下：

	@Test
	public void testHQLUpdate(){
		String hql = "DELETE FROM Department d WHERE d.id = :id";
		
		session.createQuery(hql).setInteger("id", 280)
		                        .executeUpdate();
	}

测试结果如下：

Hibernate: 
    delete 
    from
        GG_DEPARTMENT 
    where
        ID=?

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如果尝试使用HQL执行插入操作，则会抛出异常。