Mybatis 常用及复杂查询,mybatis-generator自动生成mapper接口

mybatis-generator 自动生成Mapper和Mapper.xml

没有mybatis-generator的朋友请自行百度下载

重要的事情说三遍
每一次用mybatis-generator之前都要先检查里面的src目录有没有之前生成过的文件,假如有就全部都删掉,不删掉又生成，会变成大坑,小心!!
每一次用mybatis-generator之前都要先检查里面的src目录有没有之前生成过的文件,假如有就全部都删掉,不删掉又生成，会变成大坑,小心!!
每一次用mybatis-generator之前都要先检查里面的src目录有没有之前生成过的文件,假如有就全部都删掉,不删掉又生成，会变成大坑,小心!!

这篇博客的demo是基于我上一篇博客(Mybatis持久层框架环境搭建,加简单查询,插入数据)

因为我要用自动生成的Mapper接口和Mapper.xml所以就把上篇博客用的demo的dao包和entity包下的东西都删掉了
接下来演示自动生成那些写起来很麻烦的Mapper接口和Mapper.xml

1.配置generatorConfig.xml为:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE generatorConfiguration
PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
"http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
<generatorConfiguration>

    <classPathEntry
location="mysql-connector-java-5.1.25-bin.jar"/>

    <context id="MysqlTables" targetRuntime="MyBatis3">



        <commentGenerator>
            
            <property name="suppressAllComments" value="true"/>
        </commentGenerator>

        
        <jdbcConnection driverClass="com.mysql.jdbc.Driver"
  connectionURL="jdbc:mysql://localhost:3306/mysql_demo"
  userId="root" password="root">
        </jdbcConnection>
  
  
        <javaTypeResolver>
            <property name="forceBigDecimals" value="false"/>
        </javaTypeResolver>

        
   

        <javaModelGenerator targetPackage="entity"
  targetProject="src"
  >
  
            <property name="enableSubPackages" value="true"/>
    
            <property name="trimStrings" value="true"/>
        </javaModelGenerator>

      
        <sqlMapGenerator
  targetPackage="dao"
  targetProject="src">
            <property name="enableSubPackages" value="true"/>
        </sqlMapGenerator>

   
        
        <javaClientGenerator
  type="XMLMAPPER"
  targetPackage="dao"
  targetProject="src">
            <property name="enableSubPackages" value="true"/>
        </javaClientGenerator>
        
   
    
     
        <table
  tableName="student"
  domainObjectName="Student"
  enableInsert="true"
  enableCountByExample="false"
  enableUpdateByExample="false"
  enableDeleteByExample="false"
  enableSelectByExample="false"
  selectByExampleQueryId="false">
   
  
  
  </table>

    <table tableName="teacher"
  domainObjectName="Teacher"
  enableInsert="true"
  enableCountByExample="false"
  enableUpdateByExample="false"
  enableDeleteByExample="false"
  enableSelectByExample="false"
  selectByExampleQueryId="false">
   
  
  
  </table>
    </context>
</generatorConfiguration>

table标签以上的配置,配置过一次就行了,table标签根据不同项目自己修改
我的demo有student表和teacher表

2.在cmd窗口填写命令行调用jar包
win键+R 填入cmd就会弹出cmd窗口了
根据自己下载的mybatis-generator文件夹位置,按下图输入

再按回车

此时查看mybatis-generator文件夹下的src目录里多了dao文件夹和entity文件夹
entity文件夹里自动生成了Student实体类和Teacher实体类

dao文件夹里自动生成了 Mapper接口和Mapperxml 这样的逆向生成代码才是成功的

这样就完成mybatis-generator自动生成mapper了比起自己写,简直是省了一大堆时间

假如这里说有警告,生成的也是不对的 (这里是个大坑逆向生成时存在了多个数据库,所以那里才说有一个警告要没有警告所逆向生成的Mapper才是成功的 )

例如:

虽然生成成功了,但是有个警告,这样也是不行的

一对一查询关系（一个学生对应一个老师）

当我们实体类的属性不够用时,我们要添加对象的属性,我们就要自行修改Mapper接口了
在Student实体里添加 teacher属性,为符合javabean规范也加了get和set方法

1.在Student类里加了：
private Teacher teacher;

    public Teacher getTeacher() {
        return teacher;
    }

    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }

2.修改StudentMapper.xml 在resultMap里添加association(关联),再添加teacherResultMap
StudentMapper.xml里的resultMap标签添加association联系,然后在下面再加一个关联的resultMap
<resultMap id="BaseResultMap" type="entity.Student">
    <id column="Sid" jdbcType="VARCHAR" property="sid" />
    <result column="Sname" jdbcType="VARCHAR" property="sname" />
    <result column="Sage" jdbcType="TIMESTAMP" property="sage" />
    <result column="Ssex" jdbcType="VARCHAR" property="ssex" />
    <result column="Tid" jdbcType="INTEGER" property="tid" />
    <result column="SageNum" jdbcType="INTEGER" property="sagenum" />
    <association property="teacher" resultMap="teacherResultMap"/>
</resultMap>

关联查询就要用到多表查询了,要写新的sql语句了：
<select id="selectByPrimaryKeyWithTeacher" parameterType="java.lang.String" resultMap="BaseResultMap">
    select
    <include refid="Base_Column_List" />,
    Tid,Tname,username,password
    from student s
    LEFT JOIN teacher t ON t.Tid=s.Sid
    where Sid = #{sid,jdbcType=VARCHAR}
</select>

StudenMapper.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="dao.StudentMapper" >
<resultMap id="BaseResultMap" type="entity.Student" >
    <id column="Sid" property="sid" jdbcType="VARCHAR" />
    <result column="Sname" property="sname" jdbcType="VARCHAR" />
    <result column="Sage" property="sage" jdbcType="TIMESTAMP" />
    <result column="Ssex" property="ssex" jdbcType="VARCHAR" />
    <result column="Tid" property="tid" jdbcType="INTEGER" />
    <result column="SageNum" property="sagenum" jdbcType="INTEGER" />
    <association property="teacher" resultMap="teacherResultMap"/>
</resultMap>

<sql id="Base_Column_List" >
Sid, Sname, Sage, Ssex, s.Tid, SageNum
</sql>

<select id="selectByPrimaryKeyWithTeacher" parameterType="java.lang.String" resultMap="BaseResultMap">
    select
    <include refid="Base_Column_List" />,
    t.Tid,Tname,username,password
    from student s
    LEFT JOIN teacher t ON t.Tid=s.Sid
    where Sid = #{sid,jdbcType=VARCHAR}
</select>

<select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.String" >
    select
    <include refid="Base_Column_List" />
    from student
    where Sid = #{sid,jdbcType=VARCHAR}
</select>
<delete id="deleteByPrimaryKey" parameterType="java.lang.String" >
    delete from student
    where Sid = #{sid,jdbcType=VARCHAR}
</delete>
<insert id="insert" parameterType="entity.Student" >
    insert into student (Sid, Sname, Sage,
      Ssex, Tid, SageNum)
    values (#{sid,jdbcType=VARCHAR}, #{sname,jdbcType=VARCHAR}, #{sage,jdbcType=TIMESTAMP},
      #{ssex,jdbcType=VARCHAR}, #{tid,jdbcType=INTEGER}, #{sagenum,jdbcType=INTEGER})
</insert>
<insert id="insertSelective" parameterType="entity.Student" >
    insert into student
    <trim prefix="(" suffix=")" suffixOverrides="," >
      <if test="sid != null" >
        Sid,
      </if>
      <if test="sname != null" >
        Sname,
      </if>
      <if test="sage != null" >
        Sage,
      </if>
      <if test="ssex != null" >
        Ssex,
      </if>
      <if test="tid != null" >
        Tid,
      </if>
      <if test="sagenum != null" >
        SageNum,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides="," >
      <if test="sid != null" >
        #{sid,jdbcType=VARCHAR},
      </if>
      <if test="sname != null" >
        #{sname,jdbcType=VARCHAR},
      </if>
      <if test="sage != null" >
        #{sage,jdbcType=TIMESTAMP},
      </if>
      <if test="ssex != null" >
        #{ssex,jdbcType=VARCHAR},
      </if>
      <if test="tid != null" >
        #{tid,jdbcType=INTEGER},
      </if>
      <if test="sagenum != null" >
        #{sagenum,jdbcType=INTEGER},
      </if>
    </trim>
</insert>
<update id="updateByPrimaryKeySelective" parameterType="entity.Student" >
    update student
    <set >
      <if test="sname != null" >
        Sname = #{sname,jdbcType=VARCHAR},
      </if>
      <if test="sage != null" >
        Sage = #{sage,jdbcType=TIMESTAMP},
      </if>
      <if test="ssex != null" >
        Ssex = #{ssex,jdbcType=VARCHAR},
      </if>
      <if test="tid != null" >
        Tid = #{tid,jdbcType=INTEGER},
      </if>
      <if test="sagenum != null" >
        SageNum = #{sagenum,jdbcType=INTEGER},
      </if>
    </set>
    where Sid = #{sid,jdbcType=VARCHAR}
</update>
<update id="updateByPrimaryKey" parameterType="entity.Student" >
    update student
    set Sname = #{sname,jdbcType=VARCHAR},
      Sage = #{sage,jdbcType=TIMESTAMP},
      Ssex = #{ssex,jdbcType=VARCHAR},
      Tid = #{tid,jdbcType=INTEGER},
      SageNum = #{sagenum,jdbcType=INTEGER}
    where Sid = #{sid,jdbcType=VARCHAR}
</update>
</mapper>

3.因为StudentMapper.xml里面多了一个查询方法则要在StudentMapper里面写多个方法
StudentMapper接口:
public interface StudentMapper {
int deleteByPrimaryKey(String sid);

int insert(Student record);

int insertSelective(Student record);

Student selectByPrimaryKey(String sid);

Student selectByPrimaryKeyWithTeacher(String sid);

int updateByPrimaryKeySelective(Student record);

int updateByPrimaryKey(Student record);
}

4.修改主函数:

public class Main {
    public static void main(String[] args) throws Exception {
            //加载配置文件通过io流加载xml文件
         InputStream in= Main.class.getResourceAsStream("resource/mybatis-cfg.xml");
        SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(in);
        SqlSession session= factory.openSession();
        StudentMapper mapper=session.getMapper(StudentMapper.class);
        Student student=new Student();
      student=mapper.selectByPrimaryKeyWithTeacher("1");
        session.commit();
        //关闭会话   避免占用资源
        session.close();
    }
}

运行程序:

一对多的查询关系（一个老师对应了多个学生）:

1.修改TeacherMapper.xml里的查询方法

TeacherMapper.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="dao.TeacherMapper" >

<resultMap id="BaseResultMap" type="entity.Teacher" >
    <id column="Tid" property="tid" jdbcType="INTEGER" />
    <result column="Tname" property="tname" jdbcType="VARCHAR" />
    <result column="username" property="username" jdbcType="VARCHAR" />
    <result column="password" property="password" jdbcType="VARCHAR" />
    <collection property="stuList" resultMap="stuResultMap" />
</resultMap>

<sql id="Base_Column_List" >
    t.Tid, Tname, username, password
</sql>

<select id="selectByPrimaryKeyWithStudent" parameterType="java.lang.Integer" resultMap="BaseResultMap">
    select
    <include refid="Base_Column_List" />,
    Sid, Sname, Sage, Ssex, s.Tid, SageNum
    from teacher t
    LEFT JOIN student s ON s.Tid=t.Tid
    where t.Tid = #{tid,jdbcType=INTEGER}
</select>

<select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.Integer" >
    select
    <include refid="Base_Column_List" />
    from teacher
    where Tid = #{tid,jdbcType=INTEGER}
</select>
<delete id="deleteByPrimaryKey" parameterType="java.lang.Integer" >
    delete from teacher
    where Tid = #{tid,jdbcType=INTEGER}
</delete>
<insert id="insert" parameterType="entity.Teacher" >
    insert into teacher (Tid, Tname, username,
      password)
    values (#{tid,jdbcType=INTEGER}, #{tname,jdbcType=VARCHAR}, #{username,jdbcType=VARCHAR},
      #{password,jdbcType=VARCHAR})
</insert>
<insert id="insertSelective" parameterType="entity.Teacher" >
    insert into teacher
    <trim prefix="(" suffix=")" suffixOverrides="," >
      <if test="tid != null" >
        Tid,
      </if>
      <if test="tname != null" >
        Tname,
      </if>
      <if test="username != null" >
        username,
      </if>
      <if test="password != null" >
        password,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides="," >
      <if test="tid != null" >
        #{tid,jdbcType=INTEGER},
      </if>
      <if test="tname != null" >
        #{tname,jdbcType=VARCHAR},
      </if>
      <if test="username != null" >
        #{username,jdbcType=VARCHAR},
      </if>
      <if test="password != null" >
        #{password,jdbcType=VARCHAR},
      </if>
    </trim>
</insert>
<update id="updateByPrimaryKeySelective" parameterType="entity.Teacher" >
    update teacher
    <set >
      <if test="tname != null" >
        Tname = #{tname,jdbcType=VARCHAR},
      </if>
      <if test="username != null" >
        username = #{username,jdbcType=VARCHAR},
      </if>
      <if test="password != null" >
        password = #{password,jdbcType=VARCHAR},
      </if>
    </set>
    where Tid = #{tid,jdbcType=INTEGER}
</update>
<update id="updateByPrimaryKey" parameterType="entity.Teacher" >
    update teacher
    set Tname = #{tname,jdbcType=VARCHAR},
      username = #{username,jdbcType=VARCHAR},
      password = #{password,jdbcType=VARCHAR}
    where Tid = #{tid,jdbcType=INTEGER}
</update>
</mapper>

2.在TeacherMapper里面添加方法:
TeacherMapper:
public interface TeacherMapper {
int deleteByPrimaryKey(Integer tid);

int insert(Teacher record);

int insertSelective(Teacher record);

Teacher selectByPrimaryKey(Integer tid);

Teacher selectByPrimaryKeyWithStudent(Integer tid);

int updateByPrimaryKeySelective(Teacher record);

int updateByPrimaryKey(Teacher record);
}

3.修改主函数:
public class Main {

teacher=mapper.selectByPrimaryKeyWithStudent(1);

        //mybatis自动把查询出的数据,自动映射,封装成对象大大节省了时间
        //现在看来   写StudentMapper 和StudentMapper.xml都很费时间在后面,我会在博客里说如何自动生成Mapper和Mapper.xml
        session.commit();
        //关闭会话   避免占用资源
        session.close();
    }
}

执行程序:

查询出了一个老师对象和学生列表(里面有四个学生对象)

倘若前端传来一个表单要我填入一个老师的信息和一个学生的信息

要往数据库"同时"插入学生和老师的信息
问题来了,一个老师的Tid对应一个学生的Tid,要怎样才能在插入数据库之前,学生对象拿到老师的Tid,拿到之后一个学生就能绑定一个老师了

1.修改主函数:
public class Main {

    public static void main(String[] args) throws Exception {
            //加载配置文件通过io流加载xml文件
         InputStream in= Main.class.getResourceAsStream("resource/mybatis-cfg.xml");
        SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(in);
        SqlSession session= factory.openSession();
        TeacherMapper mapper=session.getMapper(TeacherMapper.class);
        StudentMapper studentMapper=session.getMapper(StudentMapper.class);
        Teacher teacher=new Teacher();
        teacher.setPassword("123456");
        teacher.setUsername("gaga");
        //用TeacherMapper,先插入教师的信息,mybatis再把插入的Tid返回来
        mapper.insertSelective(teacher);
        Student stu=new Student();
        stu.setSagenum(12);
        stu.setSname("gugu");
        stu.setSid("20");
        stu.setTid(teacher.getTid());
        studentMapper.insertSelective(stu);
        //mybatis自动把查询出的数据,自动映射,封装成对象大大节省了时间
        //现在看来   写StudentMapper 和StudentMapper.xml都很费时间在后面,我会在博客里说如何自动生成Mapper和Mapper.xml
        session.commit();
        //关闭会话   避免占用资源
        session.close();
    }
}

2.修改TeacherMapper.xml里的插入语句:
TeacherMapper.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="dao.TeacherMapper" >

<sql id="Base_Column_List" >
t.Tid, Tname, username, password
</sql>

<select id="selectByPrimaryKeyWithStudent" parameterType="java.lang.Integer" resultMap="BaseResultMap">
    select
    <include refid="Base_Column_List" />,
    Sid, Sname, Sage, Ssex, s.Tid, SageNum
    from teacher t
    LEFT JOIN student s ON s.Tid=t.Tid
    where t.Tid = #{tid,jdbcType=INTEGER}
</select>

<insert id="insertSelective" parameterType="entity.Teacher"   useGeneratedKeys="true" keyProperty="tid">
    insert into teacher
    <trim prefix="(" suffix=")" suffixOverrides="," >
      <if test="tid != null" >
        Tid,
      </if>
      <if test="tname != null" >
        Tname,
      </if>
      <if test="username != null" >
        username,
      </if>
      <if test="password != null" >
        password,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides="," >
      <if test="tid != null" >
        #{tid,jdbcType=INTEGER},
      </if>
      <if test="tname != null" >
        #{tname,jdbcType=VARCHAR},
      </if>
      <if test="username != null" >
        #{username,jdbcType=VARCHAR},
      </if>
      <if test="password != null" >
        #{password,jdbcType=VARCHAR},
      </if>
    </trim>
</insert>
<update id="updateByPrimaryKeySelective" parameterType="entity.Teacher" >
    update teacher
    <set >
      <if test="tname != null" >
        Tname = #{tname,jdbcType=VARCHAR},
      </if>
      <if test="username != null" >
        username = #{username,jdbcType=VARCHAR},
      </if>
      <if test="password != null" >
        password = #{password,jdbcType=VARCHAR},
      </if>
    </set>
    where Tid = #{tid,jdbcType=INTEGER}
</update>
<update id="updateByPrimaryKey" parameterType="entity.Teacher" >
    update teacher
    set Tname = #{tname,jdbcType=VARCHAR},
      username = #{username,jdbcType=VARCHAR},
      password = #{password,jdbcType=VARCHAR}
    where Tid = #{tid,jdbcType=INTEGER}
</update>
</mapper>

执行程序,查看数据库:

新的教师成功关联了一个新的同学

倘若我要查询老师ID为1和2的信息（用list来查询,list集合里面包含1和2）

因为是mybatis是采用动态sql查询的所以弄的时候麻烦了一点:

1.在TeacherMapper.xml里添加selectByTids查询语句:
TeacherMapper.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="dao.TeacherMapper" >

<sql id="Base_Column_List" >
t.Tid, Tname, username, password
</sql>

<select id="selectByTids" resultMap="BaseResultMap" parameterType="list" >
    select
    <include refid="Base_Column_List" />
    from teacher t
    where t.Tid IN
    <foreach collection="tids" item="it" open="(" close=")" separator="," >
      #{it}
    </foreach>
</select>

<delete id="deleteByPrimaryKey" parameterType="java.lang.Integer" >
    delete from teacher
    where Tid = #{tid,jdbcType=INTEGER}
</delete>
<insert id="insert" parameterType="entity.Teacher" >
    insert into teacher (Tid, Tname, username,
      password)
    values (#{tid,jdbcType=INTEGER}, #{tname,jdbcType=VARCHAR}, #{username,jdbcType=VARCHAR},
      #{password,jdbcType=VARCHAR})
</insert>

2.在TeacherMapper里添加selectByTids方法:
TeacherMapper:
public interface TeacherMapper {
int deleteByPrimaryKey(Integer tid);