mybaits入门

1.回顾jdbc开发 orm概述

　　orm是一种解决持久层对象关系映射的规则，而不是一种具体技术。jdbc/dbutils/springdao，hibernate/springorm，mybaits同属于ORM解决方案之一。

2.mybaits

　　mybatis基于jdbc，兼顾难易度和速度。

3.mybatis快速入门

　　导入lib包

　　在src目录下配置mybatis.cfg.xml

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!--加载类路径下的属性文件-->
<properties resource="db.properties">
</properties>
<!--设置类型别名-->
<typeAliases>
<typeAlias type="app04.Student" alias="student"/>
</typeAliases>
<!--设置默认连接环境信息-->
<environments default="oracle_developer">
<!--连接环境信息，取一个唯一的名字-->
<environment id="mysql_developer">
<!--事务管理方式-->
<transactionManager type="jdbc"></transactionManager>
<!--使用连接池获取-->
<dataSource type="pooled">
<!--配置与数据库交互的4个必要属性-->
<property name="driver" value="${mysql.driver}"/>
<property name="url" value="${mysql.url}"/>
<property name="username" value="${mysql.username}"/>
<property name="password" value="${mysql.password}"/>
</dataSource>
</environment>
<environment id="oracle_developer">
<!--事务管理方式-->
<transactionManager type="jdbc"></transactionManager>
<!--使用连接池获取-->
<dataSource type="pooled">
<!--配置与数据库交互的4个必要属性-->
<property name="driver" value="oracle.jdbc.driver.OracleDriver"/>
<property name="url" value="jdbc:oracle:thin:@127.0.0.1:1521:orcl"/>
<property name="username" value="scott"/>
<property name="password" value="tiger"/>
</dataSource>
</environment>
</environments>
<!--加载映射文件-->
<mappers>
<mapper resource="app04/StudentMapper.xml"/>
<mapper resource="app09/StudentMapper.xml"/>
<mapper resource="app10/StudentMapper.xml"/>
<mapper resource="app11/StudentMapper.xml"/>
</mappers>
</configuration>

　　实体类

　　配置映射文件StudentMapper.xml

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="studentNamespace">
<!--映射实体与表-->
<!--type表示实体的全路径名
id为实体与表的映射取一个唯一的编号-->
<resultMap id="studentMap" type="app04.Student">
<!--id标签映射主键属性，result标签映射非主键属性
property表示实体的属性名
column表示表的字段名-->
<id property="id" column="id"/>
<result property="name" column="name"/>
<result property="sal" column="sal"/>
</resultMap>
<!--insert属性：要书写insert语句
id表示为insert语句取一个唯一编号
parameterType表示要执行的dao中的方法的参数，如果是类的话，必须使用全路径名-->
<insert id="add1">
INSERT INTO students(id,name,sal) values(1,"haha",7000)
</insert>
<insert id="add2" parameterType="student">
INSERT INTO students(id,name,sal) values(#{id},#{name},#{sal})
</insert>
</mapper>

　　获取连接

public class MybatisUtil {
private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
private static SqlSessionFactory sqlSessionFactory;
//加载位于mybatis.xml配置文件
static{
try {
Reader reader = Resources.getResourceAsReader("mybatis.cfg.xml");
sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
} catch (IOException e) {
throw new RuntimeException(e);
}
}

public static SqlSession getSqlSession(){
SqlSession sqlSession = threadLocal.get();
if(sqlSession == null){
sqlSession = sqlSessionFactory.openSession();
//将session与当前线程绑定在一起
threadLocal.set(sqlSession);
}
return sqlSession;
}
//关闭当前sqlsession，与当前线程分离
public static void closeSqlSession(){
SqlSession sqlSession = threadLocal.get();
if(sqlSession!=null){
sqlSession.close();
//分离，目的是为了尽早垃圾回收
threadLocal.remove();
}
}

}

　　dao

public void add1() throws Exception{
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
//默认事务开始，读取StudentMapper.xml映射文件中的sql语句
int i = sqlSession.insert("studentNamespace.add1");
sqlSession.commit();
System.out.println("本次操作影响了"+i+"行");
}catch (Exception e){
sqlSession.rollback();
throw e;
}finally {
MybatisUtil.closeSqlSession();
}
}
public void add2(Student student) throws Exception{
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
//默认事务开始，读取StudentMapper.xml映射文件中的sql语句
sqlSession.insert("studentNamespace.add2",student);
sqlSession.commit();
}catch (Exception e){
sqlSession.rollback();
throw e;
}finally {
MybatisUtil.closeSqlSession();
}
}

4.mybatis工作流程

1）通过Reader对象读取src目录下的mybatis.cfg.xml配置文件(该文本的位置和名字可任意)

2）通过SqlSessionFactoryBuilder对象创建SqlSessionFactory对象

3）从当前线程中获取SqlSession对象

4）事务开始，在mybatis中默认

5）通过SqlSession对象读取StudentMapper.xml映射文件中的操作编号，从而读取sql语句

6）事务提交，必写

7）关闭SqlSession对象，并且分开当前线程与SqlSession对象，让GC尽早回收

5基于MybatisUtil工具类，完成CURD操作

　　映射配置文件

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="app09.Student">
<resultMap id="studentMap" type="app09.Student">
<id property="id" column="id"/>
<result property="name" column="name"/>
<result property="sal" column="sal"/>
</resultMap>
<insert id="add" parameterType="app09.Student">
INSERT  INTO students(id,name, sal) VALUES(#{id},#{name},#{sal})
</insert>
<!--如果参数不是实体，只是普通变量，#中的参数名可以随便写-->
<select id="findById" parameterType="int" resultType="app09.Student">
SELECT ID,NAME,SAL FROM students WHERE id = #{xxx}
</select>

<select id="findAll" resultType="app09.Student">
SELECT ID,NAME,SAL FROM students
</select>

<update id="update" parameterType="app09.Student">
UPDATE students SET name=#{name},sal=#{sal} WHERE id=#{id}
</update>
<delete id="delete" parameterType="app09.Student">
DELETE  FROM students WHERE  ID=#{id}
</delete>
</mapper>

　　dao

public void add(Student student) throws Exception{
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
sqlSession.insert(Student.class.getName()+".add",student);
sqlSession.commit();
}catch (Exception e){
sqlSession.rollback();
throw e;
}finally {
MybatisUtil.closeSqlSession();
}
}
private Student findById(int id) {
Student student= null;
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
student = sqlSession.selectOne(Student.class.getName() + ".findById", id);
sqlSession.commit();
}catch (Exception e){
sqlSession.rollback();
throw e;
}finally {
MybatisUtil.closeSqlSession();
}
return student;

}

private List<Student> findAll() {
List<Student> students = new ArrayList<>();
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
students = sqlSession.selectList(Student.class.getName() + ".findAll");
sqlSession.commit();
}catch (Exception e){
sqlSession.rollback();
throw e;
}finally {
MybatisUtil.closeSqlSession();
}
return students;
}
private void update(Student student) {
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
sqlSession.update(Student.class.getName()+".update",student);
sqlSession.commit();
}catch (Exception e){
sqlSession.rollback();
throw e;
}finally {
MybatisUtil.closeSqlSession();
}
}
private void delete(Student student) {
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
sqlSession.delete(Student.class.getName()+".delete",student);
sqlSession.commit();
}catch (Exception e){
sqlSession.rollback();
throw e;
}finally {
MybatisUtil.closeSqlSession();
}
}

6.分页查询(mysql,oracle)

　　映射配置文件

mysql

<select id="findAllWithFy" parameterType="map" resultMap="studentMap">
SELECT id,name,sal FROM students LIMIT #{start},#{size}
</select>

oracle

<select id="findAllWithFyByOracle" parameterType="map" resultMap="studentMap">
SELECT ID,NAME,SAL
FROM (SELECT ROWNUM IDS,ID,NAME,SAL
FROM STUDENTS
WHERE ROWNUM < #{end})
WHERE IDS > #{start}
</select>

　　dao

public List<Student> findAllWithFy(int start,int size){
List<Student> students = new ArrayList<>();
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
Map<String, Object> map = new LinkedHashMap<>();
map.put("start",start);
map.put("size",size);
students = sqlSession.selectList(Student.class.getName()+".findAllWithFy",map);
sqlSession.commit();
return students;
}catch (Exception e){
sqlSession.rollback();
throw e;
}finally {
MybatisUtil.closeSqlSession();
}
}

7.动态SQL操作之查询

　　映射配置文件

<select id="findAll" parameterType="map" resultMap="studentMap">
SELECT ID,NAME,SAL FROM STUDENTS
<where>
<if test="pid!=null">
and ID = #{pid}
</if>
<if test="pname!=null">
and NAME = #{pname}
</if>
<if test="psal != null">
AND SAL < #{psal}
</if>
</where>
</select>

　　dao

public List<Student> findAll(Integer id ,String name,Double sal){
List<Student> students = new ArrayList<>();
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
Map<String, Object> map = new LinkedHashMap<>();
map.put("pid",id);
map.put("pname",name);
map.put("psal",sal);
students = sqlSession.selectList(Student.class.getName()+".findAll",map);
sqlSession.commit();
return students;
}catch (Exception e){
sqlSession.rollback();
throw new RuntimeException(e);
}finally {
MybatisUtil.closeSqlSession();
}
}

8.动态SQL操作之更新

　　映射配置文件

<update id="update" parameterType="map">
UPDATE STUDENTS
<set>
<if test="pname!=null">
name = #{pname},
</if>
<if test="psal != null">
sal = #{psal},
</if>
</set>
WHERE id = #{pid}
</update>

　　dao

public void update(Student student){
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
Map<String, Object> map = new LinkedHashMap<>();
map.put("pid",student.getId());
map.put("pname",student.getName());
map.put("psal",student.getSal());
sqlSession.update(Student.class.getName()+".update",map);
sqlSession.commit();
}catch (Exception e){
sqlSession.rollback();
throw new RuntimeException(e);
}finally {
MybatisUtil.closeSqlSession();
}
}

9.动态SQL操作之删除

　　映射配置文件

<delete id="deleteAll" >
DELETE FROM  students WHERE ID IN
<foreach collection="array" open="(" close=")" separator="," item="ids">
#{ids}
</foreach>
</delete>

　　dao

public void deleteAll(int... ids)throws Exception{
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
sqlSession.delete(Student.class.getName()+".deleteAll",ids);
sqlSession.commit();
}catch (Exception e){
sqlSession.rollback();
throw new RuntimeException(e);
}finally {
MybatisUtil.closeSqlSession();
}
}

10.动态SQL操作之插入

　　映射配置文件

<!--sql片段-->
<sql id="key">
<trim suffixOverrides=",">
<if test="id != null">
id,
</if>
<if test="name != null">
name,
</if>
<if test="sal != null">
sal,
</if>
</trim>
</sql>
<sql id="value">
<trim suffixOverrides=",">
<if test="id != null">
#{id},
</if>
<if test="name != null">
#{name},
</if>
<if test="sal != null">
#{sal},
</if>
</trim>
</sql>
<insert id="insert" parameterType="app11.Student">
INSERT INTO students(<include refid="key"/>) values (<include refid="value"/>)
</insert>

　　dao

public void deleteList(List<Integer> ids)throws Exception{
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
sqlSession.delete(Student.class.getName()+".deleteList",ids);
sqlSession.commit();
}catch (Exception e){
sqlSession.rollback();
throw new RuntimeException(e);
}finally {
MybatisUtil.closeSqlSession();
}
}