mybatis mapper接口开发dao层

本文将探讨使用 mapper接口，以及 pojo 包装类进行 dao 层基本开发

mybatis dao 层开发只写 mapper 接口

其中需要 开发的接口实现一些开发规范

1、 UserMapper.xml 这个配置文件中的namespace应该是 mapper 接口的地址

2、 UserMapper.java 中的方法名与UserMapper.xml 的 statementid 要保持一致

3、 第二点中的方法 输入参数 与 返回值均要 跟 UserMapper.xml 中配置好的 parametertype , resulttype 保持一致

满足这样的规范， mybatis 通过读取xxx_mapper.xml 这样的 配置文件即可通过反射创建 该 mapper 接口的 实现类。

由于涉及到的查询结果列已经不再是单纯的 pojo 对象的属性能够包含的

所以本示例代码中的对于简单java对象进行一次包装

UserOrderWrapperFirst

为啥叫这个名呢，因为我认为这个类不是终点，我可能后面还会写一个UserOrderWrapper包装类，所以暂且先叫First好了

同样老套路先上项目结构图

<?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 type="com.ghc.pojo.User" alias="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://localhost:3306/mybatis?characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="Mede645"/>

            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="mappers/UserMapper.xml"/>
    </mappers>

</configuration>

config/SqlMappingConfig.xml   mybatis全局配置文件

<?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="com.ghc.dao.UserDao">

    <select id="findUserById" parameterType="int" resultType="user">
        SELECT * FROM user WHERE id = #{id}
    </select>

    <resultMap id="findUserOrderMapper" type="com.ghc.pojo.UserOrderWrapperFirst"> <!--因为继承自Order类，所以这些都可以看做是Order这个对象的基本属性-->
        <id column="id" property="id"/>
        <result column="user_id" property="user_id"/>
        <result column="number" property="number"/>
        <result column="createtime" property="createtime"/>
        <result column="note" property="note"/>

        <!--配置映射关联的用户信息-->
        <!-- association: 用于映射关联查询单个对象的信息-->
        <!---->
        <association property="user" javaType="com.ghc.pojo.User"> <!--此处本可以写成user 但是为了突出就不用别名了 下面都是封装 wrapper 包装类的user对象到一个User的bean中-->
           <id column="user_id" property="id"/> <!--唯一标识用户的列就是主外键列 user_id 是 Order 的基本属性-->
            <result column="username" property="userName"/>
            <result column="birthday" property="birthday"/>
            <result column="sex" property="sex"/>
            <result column="address" property="address"/>
        </association>
    </resultMap>

    <select id="findUserOrder"  resultMap="findUserOrderMapper">
        select o.*,u.* from user u join orders o on u.id = o.user_id
    </select>
    <!--
    select o.*,u.* from user u join orders o on u.id = o.user_id
    -->
</mapper>

mappers/UserMapper.xml   对应mapper接口映射文件

log4j.rootLogger=DEBUG,A1
log4j.logger.org.springframework=debug
log4j.appender.A1=org.apache.log4j.ConsoleAppender
log4j.appender.A1.layout=org.apache.log4j.PatternLayout
log4j.appender.A1.layout.ConversionPattern=%d %5p [%t] (%F:%L) - %m%n

log4j.properties

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.ghc</groupId>
  <artifactId>mybatis</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>war</packaging>

  <name>mybatis Maven Webapp</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.7</maven.compiler.source>
    <maven.compiler.target>1.7</maven.compiler.target>
  </properties>

  <dependencies>

    <!-- https://mvnrepository.com/artifact/junit/junit -->
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
      <scope>test</scope>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.4.6</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/log4j/log4j -->
    <dependency>
      <groupId>log4j</groupId>
      <artifactId>log4j</artifactId>
      <version>1.2.17</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>6.0.6</version>
    </dependency>

  </dependencies>

  <build>
    <finalName>mybatis</finalName>
    <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
      <plugins>
        <plugin>
          <artifactId>maven-clean-plugin</artifactId>
          <version>3.0.0</version>
        </plugin>
        <!-- see http://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_war_packaging -->
        <plugin>
          <artifactId>maven-resources-plugin</artifactId>
          <version>3.0.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>3.7.0</version>
        </plugin>
        <plugin>
          <artifactId>maven-surefire-plugin</artifactId>
          <version>2.20.1</version>
        </plugin>
        <plugin>
          <artifactId>maven-war-plugin</artifactId>
          <version>3.2.0</version>
        </plugin>
        <plugin>
          <artifactId>maven-install-plugin</artifactId>
          <version>2.5.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-deploy-plugin</artifactId>
          <version>2.8.2</version>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>

pom.xml 项目管理文件

package com.ghc.pojo;

import java.util.Date;

public class User {
    private int id;
    private String userName;
    private Date birthday;
    private String sex;
    private String address;

    public int getId() {
        return id;
    }

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

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getSex() {
        return sex;
    }

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

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }
}

com.ghc.pojo.User 简单 java对象

package com.ghc.pojo;

import java.util.Date;

public class Orders {
    private int id;
    private int user_id;
    private String number;
    private Date createtime;
    private String note;

    public int getId() {
        return id;
    }

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

    public int getUser_id() {
        return user_id;
    }

    public void setUser_id(int user_id) {
        this.user_id = user_id;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    public Date getCreatetime() {
        return createtime;
    }

    public void setCreatetime(Date createtime) {
        this.createtime = createtime;
    }

    public String getNote() {
        return note;
    }

    public void setNote(String note) {
        this.note = note;
    }
}

com.ghc.pojo.Orders 简单 java对象

package com.ghc.pojo;

import java.util.Date;

public class UserOrderWrapperFirst extends Orders{
    private User user;
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }
}

com.ghc.pojo.UserOrderWrapperFirst 上面两个简单java对象的包装类

package com.ghc.dao;

import com.ghc.pojo.User;
import com.ghc.pojo.UserOrderWrapperFirst;

import java.util.List;

public interface UserDao {
    User findUserById(int id);
    List<UserOrderWrapperFirst> findUserOrder();
}

com.ghc.dao.UserDao 符合规范这里就只用写接口了

import com.ghc.dao.UserDao;
import com.ghc.pojo.UserOrderWrapperFirst;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.util.List;

import com.ghc.pojo.User;
public class UserDaoTest {
    private SqlSessionFactory sqlSessionFactory;
    @Before
    public void injectSqlSessionFactory() throws IOException {
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("config/SqlMappingConfig.xml"));
    }
    @Test
    public void testFindUserById(){
        UserDao userDao = sqlSessionFactory.openSession().getMapper(UserDao.class);
        User user = userDao.findUserById(1);
        System.out.println(user.getUserName());

        List<UserOrderWrapperFirst> userOrderWrapperFirstList = userDao.findUserOrder();
        for(UserOrderWrapperFirst userOrder:userOrderWrapperFirstList){
            String userName = userOrder.getUser().getUserName();
            int orderId = userOrder.getId();
            System.out.println(userName+" <-----> "+String.valueOf(orderId));

        }
    }
}

E:\mybatis\src\test\java\UserDaoTest.java下UserDaoTest 做下测试

效果图：

总结一波：

对于普通 java 对象 也就是 pojo 不能满足 mapper 映射要求的，需要扩展类集成基本的简单 java 对象，例如本例中，创建新类继承Order类，并在其内部增加一个 User 对象

用来接收 关联查询后的 用户信息，如图：

这一次算是把 pojo包装对象与 resultmap 区别于 (resultType 这个需要列名与属性名保持一致) , 做了一次demo

动态 sql 的我会另开一篇，留存配置