MyBatis使用小结

MyBatis的xml配置文件示例

<?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>    <typeAliases>        <typeAlias alias="User" type="com.xxx.mybatis.models.User" />    </typeAliases>    <environments default="development">        <environment id="development">            <transactionManager type="JDBC" />            <dataSource type="POOLED">                  <property name="driver" value="com.mysql.jdbc.Driver" />                <property name="url" value="jdbc:mysql://127.0.0.1:3306/yiibai" />                <property name="username" value="root" />                <property name="password" value="" />            </dataSource>        </environment>    </environments>    <mappers>         <mapper resource="com/xxx/mybatis/models/User.xml" />    </mappers></configuration>

该xml文件用来构建MyBatis的session factory。

MyBatis实体类

即POJO

Mapper示例

<?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="com.xxx.mybatis.models.UserMapper">    <select id="GetUserByID" parameterType="int" resultType="User">        select * from `user` where id = #{id}    </select></mapper>

最初级使用代码示例

try {    reader = Resources.getResourceAsReader("config/Configure.xml");    sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);//构建session factory} catch (Exception e) {    e.printStackTrace();}SqlSession session = sqlSessionFactory.openSession();try {    User user = (User) session.selectOne("com.yiibai.mybatis.models.UserMapper.GetUserByID", 1);    if(user!=null){        String userInfo = "名字："+user.getName()+", 所属部门："+user.getDept()+", 主页："+user.getWebsite();        System.out.println(userInfo);    }} finally {    session.close();}

使用带注解的接口消除xml mapper

通过带注解的dao接口类可以替代xml形式的mapper

public interface IUser {     @Select("select * from user where id= #{id}")     public User getUserByID(int id);}

SqlSession session = sqlSessionFactory.openSession();try {    IUser iuser = session.getMapper(IUser.class);    User user = iuser.getUserByID(1);    System.out.println("名字："+user.getName());    System.out.println("所属部门："+user.getDept());    System.out.println("主页："+user.getWebsite());} finally {    session.close();}

完全使用接口和xml mapper

接口

public interface IUser {    public List<User> getUserList();    public void insertUser(User user);    public void updateUser(User user);    public void deleteUser(int userId);    public User getUser(int id);}

xml mapper

<?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="com.yiibai.mybatis.dao.IUser">    <select id="getUser" parameterType="int"        resultType="com.xxx.mybatis.models.User">        SELECT *        FROM USER        WHERE id = #{userId}    </select>    <insert id="insertUser" parameterType="User">        INSERT INTO USER(name,        dept, website,phone)        VALUES(#{name}, #{dept}, #{website}, #{phone})    </insert>    <select id="getUserList" resultType="com.xxx.mybatis.models.User">        SELECT * FROM USER    </select>    <update id="updateUser" parameterType="User">        UPDATE USER        SET        name=        #{name},        dept = #{dept},        website = #{website},        phone = #{phone}        WHERE        id =        #{id}    </update>    <delete id="deleteUser" parameterType="int">        DELETE FROM USER WHERE id = #{id}    </delete></mapper>

注意在User.xml 配置文件中，mapper namespace=”com.yiibai.mybatis.inter.IUser” ，命名空间对应非常重要，名称不能有错，必须与我们定义的 package 和 接口一致。

使用代码

try {    reader = Resources.getResourceAsReader("config/Configure.xml");    sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);//构建session factory} catch (Exception e) {    e.printStackTrace();}try{    // 获取Session连接    SqlSession session = sqlSessionFactory.openSession();    // 获取Mapper    IUser userMapper = session.getMapper(IUser.class);    // 执行插入    User user = new User();    user.setId(0);    user.setName("Google");    user.setDept("Tech");    user.setWebsite("http://www.google.com");    user.setPhone("120");    userMapper.insertUser(user);    // 提交事务    session.commit();    System.out.println("Test insert finished...");} catch (Exception e){    e.printStackTrace();}

一对多关联，多对一关联

User用户与Post文章之间存在一对多关系

public class User implements Serializable{    private int id;    private String username;    private String mobile;    private List<Post> posts;

public class Post implements Serializable{    private int id;    private User user;    private String title;    private String content;

mapper中的一对多映射语句

<resultMap type="User" id="resultUserMap">    <result property="id" column="user_id" />    <result property="username" column="username" />    <result property="mobile" column="mobile" />    <collection property="posts" ofType="com.xxx.pojo.Post" column="userid">        <id property="id" column="post_id" javaType="int" jdbcType="INTEGER"/>            <result property="title" column="title" javaType="string" jdbcType="VARCHAR"/>        <result property="content" column="content" javaType="string" jdbcType="VARCHAR"/>     </collection></resultMap><select id="getUser" resultMap="resultUserMap" parameterType="int">    SELECT u.*,p.*    FROM user u, post p    WHERE u.id=p.userid AND id=#{user_id} </select>

mapper中的多对一映射语句

<resultMap type="Post" id="resultPostsMap">    <result property="id" column="post_id" />    <result property="title" column="title" />    <result property="content" column="content" />    <association property="user" javaType="User">          <id property="id" column="userid"/>               <result property="username" column="username"/>               <result property="mobile" column="mobile"/>           </association> </resultMap><select id="getPosts" resultMap="resultPostsMap" parameterType="int">    SELECT u.*,p.*    FROM user u, post p    WHERE u.id=p.userid AND p.post_id=#{post_id} </select>

多对多关联

在多对多关联中需要建立中间关联表的实体。
User用户与Group用户组之间存在多对多关系

public class User {    private int id;    private String username;    private String mobile;    private List<Group> groups;

public class Group {    private int groupId;    private String groupName;    private List<User> users;

public class UserGroup {    private int userId;      private int groupId;

Group的mapper配置片段

<resultMap type="Group" id="resultGroupMap_1">    <result property="id" column="id" />    <result property="groupName" column="group_name" />    <collection property="users" column="group_id"        select="com.yiibai.maper.UserGroupMaper.getUsersByGroupId" /></resultMap><select id="getGroup" resultMap="resultGroupMap_1"    parameterType="int">    SELECT *    FROM `group`    WHERE group_id=#{id}</select>

User的mapper配置片段

<resultMap type="User" id="resultUser">    <result property="id" column="group_id"/>    <result property="name" column="name"/>        <collection property="groups" column="id" select="com.yiibai.maper.UserGroupMaper.getGroupsByUserId"/></resultMap><select id="getUser" resultMap="resultUser" parameterType="int">    SELECT *    FROM user    WHERE id=#{id}</select> 

UserGroup的mapper配置片段

<!-- 根据一个用户组ID,查看这个用户组下的所有用户 --><resultMap type="User" id="resultUserMap_2">    <result property="id" column="id"/>    <result property="username" column="username"/>    <result property="mobile" column="mobile"/></resultMap><select id="getUsersByGroupId" resultMap="resultUserMap_2" parameterType="int">    SELECT u.*, ug.group_id    FROM user u, user_group ug    WHERE u.id=ug.user_id AND ug.group_id=#{group_id}</select><!-- 根据一个用户ID,查看这个用户所对应的组--><resultMap type="Group" id="resultGroupMap_2">    <result property="groupId" column="group_id"/>    <result property="groupName" column="group_name"/></resultMap> <select id="getGroupsByUserId" resultMap="resultGroupMap_2" parameterType="int">    SELECT g.*, u.user_id    FROM group g, user_group u    WHERE g.group_id=u.group_id AND u.user_id=#{user_id}</select>

MyBatis与Spring集成（非扫描mapper，mapper在配置文件中显示声明）

在集成过程中，涉及三类比较重要的文件。

1. Spring的配置文件applicationContext.xml

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">    <property name="driverClassName" value="com.mysql.jdbc.Driver" />    <property name="url" value="jdbc:mysql://127.0.0.1:3306/yiibai?characterEncoding=utf8" />    <property name="username" value="root" />    <property name="password" value="" /></bean><bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">    <property name="dataSource" ref="dataSource" />    <property name="configLocation" value="config/Configuration.xml" /></bean><bean id="userMaper" class="org.mybatis.spring.mapper.MapperFactoryBean">     <property name="sqlSessionFactory" ref="sqlSessionFactory" />    <property name="mapperInterface" value="com.xxx.maper.UserMaper" /></bean>

1. MyBatis的配置文件mybatisConfiguration.xml (可以配置MyBatis相关的setting属性)
   在mybatisConfiguration.xml中不在需要配置environments节点，但是仍要配置mappers节点（下文会通过配置spring中sqlSessionFactory内的mapperLocations，将mappers节点配置也给省略）。

2. MyBatis中的映射文件

调用Spring context中的dao接口

ctx = new ClassPathXmlApplicationContext("config/applicationContext.xml");UserMaper userMaper = (UserMaper) ctx.getBean("userMaper");// 测试id=1的用户查询，可根据数据库中的情况修改.User user = userMaper.getUserById(1);System.out.println("获取用户 ID=1 的用户名："+user.getUsername());

MyBatis与Spring集成（扫描mapper，mapper无需在配置文件中显示声明）

如果想使用MyBatis的扫描mapper的功能，需要在Spring中增加配置。

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">    <property name="dataSource" ref="dataSource" />    <property name="configLocation" value="classpath:config/Configuration.xml" />    <property name="mapperLocations" value="classpath*:com/yiibai/mapepr/*.xml" />    //不在需要在mapper中指定type全限定名    <property name="typeAliasesPackage" value="com.xxx,com.yyy"/></bean><bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">    <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory" />    <property name="basePackage" value="com.xxx.maper" />    //可以指定扫描包下面有特殊注解的mapper类    <property name="annotationClass" value="com.xxx.common.persistence.annotation.MyBatisDao"/></bean>

通过自动注入，可以将dao接口的实现注入到具体的service中。

@Autowiredprivate UserMapper userMapper;

更多参考官方文档：http://www.mybatis.org/mybatis-3/zh/index.html