Hibernate HQL以及相关方法

纸上得来终觉浅

1.首先Hibernate有以下几种检索方式：

1)导航对象图检索方式：根据已经加载的对象导航到其他对象，比如前面文章讲到的关联方式，A对B，A可以加载B，那么只要获取A对象，就可以获取到B对象；

2)OID检索方式，按照对象的OID来检索对象，比如get和load方法；

3)HQL检索  (Hibernate query language),一种面向对象的查询，查询的结果面向对象。

4)QBC检索，对查询语句进行封装，更加面向对象，同时查询语句也面向对象。

5)本地SQL，就是一般的sql了。

2.HQL检索：

1)先创建表格以及添加数据(采用之前文章讲述的双向一对多的关联方式)：

Teacher类：

package roadArchitectWeb;

import java.util.HashSet;
import java.util.Set;

public class Teacher {
	private Integer Id;
	private String Name;
	private String PhoneNum;
	private Set Students = new HashSet<>();

	public Set getStudents() {
		return Students;
	}
	public void setStudents(Set students) {
		Students = students;
	}
	public Integer getId() {
		return Id;
	}
	public void setId(Integer id) {
		Id = id;
	}
	public String getName() {
		return Name;
	}
	public void setName(String name) {
		Name = name;
	}
	public String getPhoneNum() {
		return PhoneNum;
	}
	public void setPhoneNum(String phoneNum) {
		PhoneNum = phoneNum;
	}
	public  Teacher() {
	}
	@Override
	public String toString() {
		return "Teacher [Id=" + Id + ", Name=" + Name + ", PhoneNum=" + PhoneNum + ", Students=" + Students + "]";
	}
}

Student类：

package roadArchitectWeb;

import java.util.HashSet;
import java.util.Set;

public class Student {
	private Integer Id;
	private String sName;
	private String Age;
	private Teacher teacher;
	public Teacher getTeacher() {
		return teacher;
	}
	public void setTeacher(Teacher teacher) {
		this.teacher = teacher;
	}
	public Integer getId() {
		return Id;
	}
	public void setId(Integer id) {
		Id = id;
	}
	public String getsName() {
		return sName;
	}
	public void setsName(String sName) {
		this.sName = sName;
	}
	public String getAge() {
		return Age;
	}
	public void setAge(String age) {
		Age = age;
	}
	@Override
	public String toString() {
		return "Student [Id=" + Id + ", sName=" + sName + ", Age=" + Age + ", teacher=" + teacher + "]";
	}
	public Student(){
	}
}

Teacher和Student配置文件：

hibernate配置文件：

    
    root
    123456
    com.mysql.jdbc.Driver
    jdbc:mysql://localhost/roadarchitectweb
    
    org.hibernate.dialect.MySQL5InnoDBDialect
    true
    true
    update
    
    10
    5
    2
    
    2000
    2000
    
    10
    
    false
    
    
    

测试类：

package roadArchitectWeb;
import java.util.ArrayList;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.Test;

public class HibernateTest {
	@Test
	public void test() {
		SessionFactory sessionFactory = null;
		Configuration configuration = new Configuration().configure();
		sessionFactory = configuration.buildSessionFactory();
		Session session = sessionFactory.openSession();
		Transaction transaction = session.beginTransaction();
		
		/*begin*/
		Teacher teacher = new Teacher();
		Student student = new Student();
		teacher.setName("T1");
		teacher.setPhoneNum("T18788837117");
		student.setsName("S1");
		student.setAge("S10");
		student.setTeacher(teacher);
		session.save(student);
		session.save(teacher);
		
		Teacher teacher2 = new Teacher();
		Student student2 = new Student();
		teacher2.setName("T2");
		teacher2.setPhoneNum("T28788837117");
		student2.setsName("S2");
		student2.setAge("S20");
		student2.setTeacher(teacher2);
		session.save(student2);
		session.save(teacher2);
		
		Student student3 = new Student();
		student3.setsName("S3");
		student3.setAge("S30");
		student3.setTeacher(teacher);
		session.save(student3);
		
		Student student4 = new Student();
		student4.setsName("S4");
		student4.setAge("S40");
		student4.setTeacher(teacher);
		session.save(student4);
		
		Student student5 = new Student();
		student5.setsName("S5");
		student5.setAge("S50");
		student5.setTeacher(teacher2);
		session.save(student5);
		
		Student student6 = new Student();
		student6.setsName("S6");
		student6.setAge("S60");
		student6.setTeacher(teacher2);
		session.save(student6);
		
		/*按参数位置绑定(?)或者按参数名称(:Id)绑定*/
		//1.创建Query对象
//		String hql = "from Student a where a.sName like ? and a.teacher = ? and a.Id > :Id";
//		Query query = session.createQuery(hql);
		
		//2.绑定参数
//		Teacher teacher = new Teacher();
//		teacher.setId(2);
//		query.setString(0, "%S%")
//		.setInteger("Id", 1)
//		.setEntity(1,teacher);
		
		//3.执行查询
//		java.util.List list = query.list();
//		System.out.println("HibernateTest.test():"+list.size());
		
		transaction.commit();
		session.close();
		sessionFactory.close();
	}
}

2)HQL是面向对象的，它的机制就是经过hibernate翻译为sql，写hql时候，只关注类和类的属性：

在标准sql中应该写表名的地方写类型，列名的地方写属性名，如：Student是类名，sName是属性名：

/*按参数位置绑定(?)或者按参数名称(:Id)绑定*/
		//1.创建Query对象
		String hql = "from Student a where a.sName like ? and a.teacher = ? and a.Id > :Id";
		Query query = session.createQuery(hql);
		
		//2.绑定参数
		Teacher teacher = new Teacher();
		teacher.setId(2);
		query.setString(0, "%S%")
		.setInteger("Id", 1)
		.setEntity(1,teacher);
		
		//3.执行查询
		java.util.List list = query.list();
		System.out.println("HibernateTest.test():"+list.size());

3)hibernate分页：

 setFirstResult指定查询第几页的数据，setMaxResult指定一页显示多少数据；查询的结果就是first页的max条数据：

//1.创建Query对象
		String hql = "from Student a where a.sName like ? ";
		Query query = session.createQuery(hql);
		
		//2.绑定参数  setFirstResult指定查询第几页的数据，setMaxResult指定一页显示多少数据；查询的结果就是first页的max条数据
		query.setString(0, "%S%")
		.setFirstResult(2)
		.setMaxResults(2);
		
		//3.执行查询
		java.util.List list = query.list();
		System.out.println("HibernateTest.test():"+list.size());

4)投影查询：查询的结果转换为对象的格式

查询的结果为List，里面的每条数据都是一条记录，要想将一条数据转化为一个对象，就要使用hibernate的投影查询：

查询的结果要与类映射，首先要在Student类中新增一个构造器：

public Student(Integer id, String sName, String age, Teacher teacher) {
		super();
		Id = id;
		this.sName = sName;
		Age = age;
		this.teacher = teacher;
	}

		//1.创建Query对象
		String hql = "select new Student(a.Id,a.sName,a.Age,teacher) from Student a where a.sName like ? ";
		Query query = session.createQuery(hql);
		
		//2.绑定参数  setFirstResult指定查询第几页的数据，setMaxResult指定一页显示多少数据；查询的结果就是first页的max条数据
		query.setString(0, "%S%");
		
		//3.执行查询
		java.util.List list = query.list();
		/*可以使用getsName方法了*/
		for(Student studentT:list){
			System.out.println("HibernateTest.test():"+studentT.getsName());
		}

5)Hql还可以使用groupby和having以及其他聚合函数，同标准SQL相同。