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<Student> Students = new HashSet<>();
public Set<Student> getStudents() {
return Students;
}
public void setStudents(Set<Student> 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：
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2016-4-21 19:24:31 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
<class name="roadArchitectWeb.Teacher" table="TEACHER">
<id name="Id" type="java.lang.Integer">
<column name="ID" />
<generator class="native" />
</id>
<property name="Name" type="java.lang.String">
<column name="NAME" />
</property>
<property name="PhoneNum" type="java.lang.String">
<column name="PHONENUM" />
</property>
<set name="Students" table="STUDENT">
<!-- 这里的column与many-to-one中生成的column一致 -->
<key column="teacherId"></key>
<one-to-many class="roadArchitectWeb.Student"/>
</set>
</class>
</hibernate-mapping>
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2016-4-21 19:12:13 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping package="roadArchitectWeb">
<class name="Student" table="STUDENT">
<id name="Id" type="java.lang.Integer">
<column name="ID" />
<generator class="native">
</generator>
</id>
<property name="sName" type="java.lang.String">
<column name="SNAME" />
</property>
<property name="Age" type="java.lang.String">
<column name="AGE" />
</property>
<many-to-one name="teacher" class="Teacher"
column="teacherId">
</many-to-one>
</class>
</hibernate-mapping>hibernate配置文件：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="connection.username">root</property>
<property name="connection.password">123456</property>
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost/roadarchitectweb</property>
<property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
<property name="show_sql">true</property>
<property name="format_sql">true</property>
<property name="hbm2ddl.auto">update</property>
<property name="hibernate.c3p0.max_size">10</property>
<property name="hibernate.c3p0.min_size">5</property>
<property name="c3p0.acquire_increment">2</property>
<property name="c3p0.idle_test_period">2000</property>
<property name="c3p0.timeout">2000</property>
<property name="c3p0.max_statements">10</property>
<property name="hibernate.temp.use_jdbc_metadata_defaults">false</property>
<mapping resource="roadArchitectWeb/Student.hbm.xml"/>
<mapping resource="roadArchitectWeb/Teacher.hbm.xml"/>
</session-factory>
</hibernate-configuration>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<Student> 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<Student> 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<Student> 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<Student> 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。