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mybatis映射文件mapper.xml的具體寫法

更新時間：2021年09月09日 16:39:27 作者：鈣奶加辣條。

在開發(fā)過程中，需要開發(fā)人員配置mapper映射文件，本文主要介紹了mybatis映射文件mapper.xml的具體寫法，感興趣的可以了解一下

Mapper映射文件是一個xml格式文件，必須遵循相應的dtd文件規(guī)范

在學習mybatis的時候我們通常會在映射文件這樣寫：

<?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.qbd.mapper.StudentMappers">
    <select id="findbyid" parameterType="Integer" resultMap="StudentResult">
        select *from student where id=#{id}
    </select>
    
    <select id="findbygradeid" parameterType="Integer" resultMap="StudentResult">
        select *from student where gid=#{gid}
    </select>
    
    <resultMap type="Student" id="StudentResult">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="age" column="age"/>
        <association property="address" column="addid" select="com.qbd.mapper.AddressMappers.findbyid">    
        </association>
        <association property="grade" column="gid" select="com.qbd.mapper.GradeMappers.findbyid">    
        </association>
    </resultMap>
</mapper>

然后再寫dao的實現(xiàn)在寫一個類，來實現(xiàn)dao的接口。但是這樣在實現(xiàn)中需要這樣寫：

package com.qbd.service;
import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;
 
import com.qbd.mapper.StudentMappers;
import com.qbd.model.Student;
import com.qbd.util.SqlSessionFactoryUtil;
 
public class StudentService {
    private static Logger logge=Logger.getLogger(StudentService.class);
    public static void main(String[] args) {
        SqlSession sqlSession=SqlSessionFactoryUtil.getSqlSession();
        
        StudentMappers studentMappers=(StudentMappers)sqlSession.getMapper(StudentMappers.class);
        Student student=new Student();
        student.setName("22");
        student.setAge(2);
        int s=studentMappers.add(student);
        sqlSession.commit();
        if(s>0){
            logge.info("success");
            System.out.println("success");
        }
        
    }
}

來讀取配置文件

另一種方法就是：

直接在mapper.xml中的這一部分寫成dao<mapper namespace="com.qbd.mapper.StudentMappers">如下

<?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.qbd.ssm.dao.UserDao">
    <!-- 定義緩存  一般是一級緩存，如果用同一個sqlsession 那么相同查詢直接會從緩存中查找 
    <cache size="1024" flushInterval="60000" eviction="LRU" readOnly="false"></cache>
    -->
    <!-- 查找所有 -->
    <select id="find" parameterType="Map" resultMap="StudentResult">
        select * from user
        <where>
            <if test="uname!=null and uname!='' ">
                and uname like #{uname}
            </if>
        </where>
        <if test="start!=null and size!=null">
            limit #{start},#{size}
        </if>
    </select>
    
    <select id="getTotal" parameterType="Map" resultType="Long">
        select count(*) from user
        <where>
            <if test="uname!=null and uname!='' ">
                and uname like #{uname}
            </if>
        </where>
    </select>
    <!-- 按照用戶名和密碼查找 -->
    <select id="getUser" resultMap="StudentResult" parameterType="Map">
        select *from user where uname=#{uname} and upassword=#{upassword}
    </select>
    <!-- 刪除 -->
    <delete id="delete" parameterType="Map">
        delete from user where uid=#{uid}
    </delete>
    <!-- 修改 -->
    <update id="update" parameterType="User">
        update user
        <set>
            <if test="uname!=null">
                 uname=#{uname},
            </if>
            <if test="upassword!=null">
                upassword=#{upassword},
            </if>
            <if test="upower!=null">
                upower=#{upower},
            </if>
        </set>
        where uid=#{uid}
    </update>
    <!-- 增加 -->
    <insert id="add" parameterType="User">
        insert into user values(null,#{uname},#{upassword},#{upower})
    </insert>
    <resultMap type="User" id="StudentResult">
        <id property="uid" column="uid"/>
        <result property="uname" column="uname"/>
        <result property="upassword" column="upassword"/>
    </resultMap>
</mapper>

那么就不用寫dao的實現(xiàn)在service中就能掉用 mybatis默認會把mapper.xml映射為dao的實現(xiàn)

那么下面dao就能這樣寫：

package com.qbd.ssm.dao;
 
import java.util.List;
import java.util.Map;
 
import org.apache.ibatis.annotations.Delete;
 
import com.qbd.ssm.model.User;
 
public interface UserDao {
 
    public List<User> getAll();
    public User getUser(User user);
    public int delete(User user);
    public int update(User user);
    public int add(User user);
    public List<User> find(Map<String,Object> map);
    public Long getTotal(Map<String,Object> map);
}

service這樣寫

package com.qbd.ssm.service;
import java.util.List;
import java.util.Map;
import com.qbd.ssm.model.User; 
public interface UserService {
 
    public List<User> getAll();
    public User getUser(User user);
    public int delete(User user);
    public int update(User user);
    public int add(User user);
    public List<User> find(Map<String,Object> map);
    public Long getTotal(Map<String,Object> map);
}

service的實現(xiàn)：

package com.qbd.ssm.serviceimpl;
import java.util.List;
import java.util.Map;
import javax.annotation.Resource; 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.qbd.ssm.dao.UserDao;
import com.qbd.ssm.model.User;
import com.qbd.ssm.service.UserService;
 
@Service("userService")
public class UserServiceImpl implements UserService {
 
    private UserDao userDao;
    
    public UserDao getUserDao() {
        return userDao;
    }
 
    @Resource
    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }
 
    public List<User> getAll() {
        // TODO Auto-generated method stub
        return userDao.getAll();
    }
 
    public User getUser(User user) {
        // TODO Auto-generated method stub
        return userDao.getUser(user);
    }
 
    public int delete(User user) {
        // TODO Auto-generated method stub
        return userDao.delete(user);
    }
 
    public int update(User user) {
        // TODO Auto-generated method stub
        return userDao.update(user);
    }
 
    public int add(User user) {
        // TODO Auto-generated method stub
        return userDao.add(user);
    }
 
    public List<User> find(Map<String, Object> map) {
        // TODO Auto-generated method stub
        return userDao.find(map);
    }
 
    public Long getTotal(Map<String, Object> map) {
        // TODO Auto-generated method stub
        return userDao.getTotal(map);
    }
}

在這里面userDao不能寫錯，spring會按照name進行注入

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