Hibernate入门

2016-10-04 本文已影响62人篱开罗

慕课网Hibernate学习笔记

开发环境

eclipse mars
hibernate toos

最简单的例子

创建java Project
导入相关依赖

导入hibernate-re...\lib\required中的jar包
导入mysql驱动
导入Junit4包

创建hibernate.cfg.xml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.user">root</property>
        <property name="connection.password">root</property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/hibernate?useUnicode=true&characterEncoding=UTF-8</property>
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
        
        <property name="show_sql">true</property>
        <property name="format_sql">true</property>
        <property name="hbm2ddl.auto">update</property>
    </session-factory>
</hibernate-configuration>

创建持久化类(javabean)

公有
提供不带参数的的构造方法
属性私有
有setter和getter

public class Student {
    private int id;
    private String name;
    private String sex;
    private int age;

    public Student() {
    }

    public Student(int id, String name, String sex, int age) {
        this.id = id;
        this.name = name;
        this.sex = sex;
        this.age = age;
    }
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", sex=" + sex + ", age=" + age + "]";
    }

}

创建对象关系映射文件(*.hbm.xml)

    <?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 2016-10-2 16:35:18 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
    <class name="Student" table="STUDENT">
        <id name="id" type="int">
            <column name="ID" />
            <generator class="assigned" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="NAME" />
        </property>
        <property name="sex" type="java.lang.String">
            <column name="SEX" />
        </property>
        <property name="age" type="int">
            <column name="AGE" />
        </property>
    </class>
</hibernate-mapping>

将映射添加到hibernate.cfg.xml

 <mapping resource="Student.hbm.xml"/>

创建JUnit测试类

public class StudentTest {
    
    private SessionFactory sessionFactory;
    private Session session;
    private Transaction transaction;
    
    @Before 
    public void init(){
        StandardServiceRegistry registry = new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();
        sessionFactory = new MetadataSources(registry).buildMetadata().buildSessionFactory();
        session = sessionFactory.openSession();
        transaction = session.beginTransaction();
    }
    
    @After
    public void destroy(){
        transaction.commit();
        session.close();
        sessionFactory.close();
    }
    
    @Test
    public void testSaveStudent() {
        Student student = new Student(2, "老王", "男", 13);
        session.save(student);
    }
}

运行测试即可将数据存入数据库

Hibernate相关介绍

hibernat.cfg.xml属性介绍

hibernat.show_sql:(true|false)是否输出sql语句到控制台
hibernat.format_sql: (true|false)是否对输出的sql语句进行排版
hbm2ddl.auto:(create|update|create-drop|va|idate)
create每次插入都会删除原来的表，update会更新原来的表
hibernate.default_schema:(hibernate)设置默认数据库，会在sql语句中的表名前加入前缀
hibernate.dialect:(org.hibernate.dialect.MySQLDialect)数据库方言，可针对特定数据库进行优化
hibernate.current_session_contex_class:(thread|jta):
用于指定getCurrentSession是获取本地事务还是全局事务

session

SessionFactory一个系统一般只创建一个
openSession每次获取的事务时不同事务
getCurrentSession获取的是同一个事务，会自动关闭
通过session进行增删改查
操作前需开启transaction，完成后提交transaction

*.hbm.xml配置文件介绍

<hibernate-mapping
schema="schema_name"
catalog="catalog_name"//目录mysql不支持
default_cascade="cascade_style"//级联风格
default_access="field|property|ClassName"//访问策略
default-lazy="true|false"//加载策略
package="packageName"
>
<id>
<generator class="assigned|native|increment"/>
</id>
//组件属性
<component name="address" class=""> 
    <property name="" column></property>
</component>

增删改查

save
update
delete
get //一次性获取
load // 懒加载

一对多

实体类中设置多方的set
在一方的映射文件中设置

<set name="students" table="student" lazy="true" inverse="true" cascade="all">//inverse=true表示由多方维护关联关系（多方add元素后，插入时不会出现update）
//cascade="all|save-update|delete|none"
    <key column="gid"></key>
    <one-to-many class="student">
</set>

多对一

在实体类中设置一方的实例
在多方映射文件中设置

<many-to-one name="grade" class="Grade" conlumn = "gid"></many-to-one>

HQL语句

select xxx from xxx where xxx group by xxx having xxx order by xxx

使用方法

大小写敏感
简单例子

    @Test
    public void testQuery(){
        String hql = "from Student as s";
        List<Student> students = session.createQuery(hql).list();
        for(Student student : students){
            System.out.println(student);
        }
    }

返回Object[]

//只选择一个属性则返回object
    @Test
    public void testSelect(){
        String hql = "select s.id, s.name from Student as s";
        Query<Object[]> query = session.createQuery(hql);
        List<Object[]> list = query.list();
        for(Object[] objects : list){
            System.out.println(objects[0]);
            System.out.println(objects[1]);
        }
    }

返回list

    @Test
    public void testSelectWithList(){
        String hql = "select new list(s.id, s.name) from Student as s";
        Query query = session.createQuery(hql);
        List<List> lists = query.list();
        for(List list : lists){
            System.out.println(list.get(0));
            System.out.println(list.get(1));
        }
    }

返回自定义类

//需要有相应的构造方法
String hql = "select new Student(s.id, s.name) from Student as s"
List<Student> lists = query.list();

没有指定构造器会调用默认构造器即无参构造函数
集合运算"from grade g where g.students is not empty";
获取单个对象

    @Test
    public void testGetOne(){
        String hql="from Student as s where s.id=1";
        Query query = session.createQuery(hql);
        Student student = (Student) query.uniqueResult();
        System.out.println(student.getName());
    }

Hibernate 缓存

一级缓存

与session相同的生命周期
示例代码

    @Test
    public void testCache(){
        Student student1 = session.get(Student.class, 1);
        //清除指定对象缓存
        session.evict(student1);
        //清除所有缓存
        session.clear();
        Student student2 = session.get(Student.class, 1);
        //list()不使用缓存
        String hql = "from Student";
        Query query = session.createQuery(hql);
        List<Student> students = query.list();
        //iterator 先从数据库获取所有id，判断缓存中是否有对应记录，若有则直接使用缓存
        Iterator iterator = query.iterate();
        while(iterator.hasNext()){
            Student student = (Student) iterator.next();
            System.out.println(student.getName());
        }
    }

Hibernate注解

类级别注解

@Entity(name="tableName")
@table(name="", catalog="", schema="")
@Embeddable // 在嵌入类上添加（如Address类）

属性级别注解

可写在属性上也可以写在get方法上

@Id
//多个属性Id实体类需要实现serializable接口
//字符串主键需要通过@Column指定长度
@GeneratedValue(strategy=(), generator="")
//主键生成策略

@GeneratedValue(generator="id")
@GenericGenerator(name="id", strategy="assigned")

@Column(length="", name="", nullable="", insertable="", unique="", updateable="")
@Embedded
//嵌入类需要@Embeddable
@EmbeddedId
//嵌入类（需要@Embeddable,实现Serializable接口，有无参构造方法，覆盖equals,hashCode）作为主键
@Transient
//忽略某个字段，不映射到数据库

关联映射注解

@OneToOne(cascade=CascadeType.ALl, mappedBy="id")
//mappedBy设置主控放
@JoinColumn(name="id", unique=true)
@ManyTOOne(cascade={CascadeType.ALL} fetch=FetchType.EAGER)
//fetch抓取策略默认积极
@JoinColumn(name="gid", referenceColumnName="gid")
@OneToMany(cascade={CascadeType.ALL} fetch=FetchType.LAZY)
@JoinColumn(name="gid")
@ManyToMany(mappedBy="")
@JoinTable(name="",JoinColumns="",
inverseJoinColumns={@JoinColumn(name="tid")})

Hibernate入门

开发环境

最简单的例子

Hibernate相关介绍

hibernat.cfg.xml属性介绍

session

*.hbm.xml配置文件介绍

增删改查

一对多

多对一

HQL语句

Hibernate 缓存

一级缓存

Hibernate注解

类级别注解

属性级别注解

关联映射注解

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