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映射文件：

主要是在xxxmapper.xml文件里的配置

映射文件指导这MyBatis如何进行数据库的增删该查，有着很重要的意义。

下面开始进入正题，最后会发一个完整版的代码

因为实现的主要内容是增删改查，所以我们现在接口类中定义好相关的方法，后面不在进行单一的定义！

工程的目录如下：

EmployeeMapper.java

package com.MrChengs.dao;

import java.util.Map;

import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

import com.MrChengs.bean.Employee;

public interface EmployeeMapper {

　　//我们直接传入map
    public Employee getByMap(Map<String,Object> map);
   
    //查询满足两个条件的数据
    public Employee getByIdAndNames(@Param("id")int id,@Param("name")String name);
    
    //查询
    public Employee getEmployee(int id);
    
    //增加
    public void addEmp(Employee employee);
    
    //更新
    public void updateEmp(Employee employee);
    
    //删除
    public void deleteById(int id);    
}

1）insert-映射插入语句

1.1）EmployeeMapper.xml

　　<insert id="addEmp" >

           　　insert into test(name,gender,email) values(#{name},#{gender},#{email})

     </insert>

1.2）在测试类中MyBatisTest.java

　　 @Test
     public void test2() throws IOException{
           //1.得到SqlSeesionFactory
           SqlSessionFactory sessionFactory = getSqlSessionFactory();
           //2.得到SqlSession
           SqlSession sqlSession = sessionFactory.openSession();
           try{
                EmployeeMapper mapper = (EmployeeMapper) sqlSession.getMapper(EmployeeMapper.class);
                //手动添加数据：
                Employee em = new Employee( "zhangsan", "boy", "[email protected]");
                mapper.addEmp(em);
                //手动提交数据
                sqlSession.commit();
           }finally{
                sqlSession.close(); }}

1.3)测试成功

2）update映射更新语句

2.1）EmployeeMapper.xml

 <update id="updateEmp">
           update test set name=#{name},gender=#{gender} where id=#{id}
     </update>

2.2）测试类中

   @Test
     public void test3() throws IOException{
           //1.得到SqlSeesionFactory
           SqlSessionFactory sessionFactory = getSqlSessionFactory();
           //2.得到SqlSession
           SqlSession sqlSession = sessionFactory.openSession();
           try{
                EmployeeMapper mapper = (EmployeeMapper) sqlSession.getMapper(EmployeeMapper.class);
                //手动添加数据：
                Employee em = new Employee( 6,"Jerry", "gril", null);
                mapper.updateEmp(em);
                //手动提交数据
                sqlSession.commit();
           }finally{
                sqlSession.close();}}

2.3）测试成功！

3）delete-映射删除操作

3.1）EmployeeMapper.xml

     <delete id="deleteById">
           delete from test where id=#{id}
     </delete>

3.2）测试类中

 @Test
     public void test4() throws IOException{
           //1.得到SqlSeesionFactory
           SqlSessionFactory sessionFactory = getSqlSessionFactory();
           //2.得到SqlSession
           SqlSession sqlSession = sessionFactory.openSession();
           try{
                EmployeeMapper mapper = (EmployeeMapper) sqlSession.getMapper(EmployeeMapper.class);
                //手动添加数据：
                mapper.deleteById(6);
                //手动提交数据
                sqlSession.commit();
           }finally{
                sqlSession.close();}}

3.3）测试成功！

4）关于主键的值问题

有时候需要用到主键值的问题，所以我们需要去学习这个知识点！

4.1）EmployeeMapper.xml

    <!-- useGeneratedKeys="true"使用自增主键获取主键的值 -->
    <!-- keyProperty=""接受对应的主键值-->
    <insert id="addEmp" useGeneratedKeys="true"  keyProperty="id">
        insert into test(name,gender,email) values(#{name},#{gender},#{email})
    </insert>

4.2)测试类

　　@Test
    public void test2() throws IOException{
        //1.得到SqlSeesionFactory
        SqlSessionFactory sessionFactory = getSqlSessionFactory();
        //2.得到SqlSession
        SqlSession sqlSession = sessionFactory.openSession();
        try{
            EmployeeMapper mapper = (EmployeeMapper) sqlSession.getMapper(EmployeeMapper.class);
            //手动添加数据：
            Employee em = new Employee( "zhangsan", "boy", "[email protected]");
            mapper.addEmp(em);
            //获取主键值的属性值进行打印
            System.out.println(em.getId());
            //手动提交数据
            sqlSession.commit();
        }finally{
            sqlSession.close();
        }
    }

4.3）测试成功

5）参数处理

5.1）单个参数：MyBatis不会做任何处理

　　 #{参数名} ：取出参数值

5.1.1）xml配置文件中

<select id="getId" resultType="com.MrChengs.bean.Employee">
        select id,name,gender,email from test where id = #{idabc}
    </select>

5.1.2）测试类

@Test
    public void test() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);        
        SqlSessionFactory sqlSessionFactory = (SqlSessionFactory) new 
                SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
        try{
            Employee employee =  session.selectOne("getId",5);
            System.out.println(employee);
        }finally{
            session.close();
        }
    }

5.1.3）测试是成功的！

5.2）多个参数时

MyBatis会做特殊的处理

多个参数时封装成map

key param1 ,param2......

value 传入的值

5.2.1）接口类中的查询代码设计如上所展示的

public Employee getByIdAndNames(@Param("id")int id,@Param("name")String name);

此时去掉@param：

public Employee getByIdAndNames(int id,String name);

5.2.2) xml文件

<select id="getByIdAndNames" resultType="com.MrChengs.bean.Employee" >
        select id,name,gender,email from test where id = #{id} and name=#{name}
 </select>

5.2.3）测试代码

　　@Test
    public void test5() throws IOException{
                SqlSessionFactory sessionFactory = getSqlSessionFactory();
                SqlSession sqlSession = sessionFactory.openSession();
                try{
                    EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
                    Employee employee = mapper.getByIdAndNames(5, "MrChengs");
                    System.out.println(employee);
                }finally{
                    sqlSession.close();
                }
    }

5.2.4）此时会报错

5.2.5）处理方案：是在EmployeeMapper.xml文件中修改的

<!-- 同时使用两个参数进行数据库的查询 -->
    <!-- public Employee getByIdAndNames(int id,String name); -->
    <select id="getByIdAndNames" resultType="com.MrChengs.bean.Employee" >
        select id,name,gender,email from test where id = #{param1} 
　　　　　　and name=#{param2}
 </select>

此时得到正确的答案！

5.3）多个查询字段时推荐使用的命名字段

明确指定封装参数时的map和key @param("id")

key:使用@param指定的值

5.3.1）接口类中

public Employee getByIdAndNames(@Param("id")int id,@Param("name")String name);

5.3.2）xml文件中

<select id="getByIdAndNames" resultType="com.MrChengs.bean.Employee" >
        select id,name,gender,email from test where id = #{id} and name=#{name}
</select>

测试类是5.2.3中的测试类，此时可以得到正确的结果！

5.4）

pojo：

如果参数过多，正好是业务逻辑的数据模型，我们直接传入pojo刚刚好

#{属性名} ：取出传入的pojo的属性值

如果多个参数不是业务逻辑数据，没有对应pojo，为了方法我们也可以直接传入map

#{key}就是取出对应的值

5.4.1）接口类中的

  public Employee getByMap(Map<String,Object> map);

5.4.2）xml文件中添加

<select id="getByMap" resultType="com.MrChengs.bean.Employee" >
           select id,name,gender,email from test where id = #{id} and name=#{name}
</select>

5.4.3）测试类

　　@Test
    public void test6() throws IOException{
                SqlSessionFactory sessionFactory = getSqlSessionFactory();
                SqlSession sqlSession = sessionFactory.openSession();
                try{
                    EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
                    Map<String, Object> map = new HashMap<>();
                    map.put("id", 5);
                    map.put("name", "MrChengs"); 
                    Employee employee = mapper.getByMap(map);
                    System.out.println(employee);
                }finally{
                    sqlSession.close();
                }
    }

运行时，可以正确输出结果!

5.5）思考问题注意

MyBatis(3)-映射文件

未完，待更新....

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