Mybatis - 一对一，一对多，多对多

• pojo

  public class Car implements Serializable {
        
        
      private Integer id;
      private String name;
      private Integer uId;
  
      private User user;
  
      public Integer getId() {
        
        
          return id;
      }
  
      public void setId(Integer id) {
        
        
          this.id = id;
      }
  
      public String getName() {
        
        
          return name;
      }
  
      public void setName(String name) {
        
        
          this.name = name;
      }
  
      public Integer getuId() {
        
        
          return uId;
      }
  
      public void setuId(Integer uId) {
        
        
          this.uId = uId;
      }
  
      public User getUser() {
        
        
          return user;
      }
  
      public void setUser(User user) {
        
        
          this.user = user;
      }
  
      @Override
      public String toString() {
        
        
          return "Car{" +
                  "id=" + id +
                  ", name='" + name + '\'' +
                  ", uId=" + uId +
                  '}';
      }
  }
  

  public class User implements Serializable {
        
        
      private Integer id;
      private String name;
      
      public Integer getId() {
        
        
          return id;
      }
  
      public void setId(Integer id) {
        
        
          this.id = id;
      }
  
      public String getName() {
        
        
          return name;
      }
  
      public void setName(String name) {
        
        
          this.name = name;
      }
  
      @Override
      public String toString() {
        
        
          return "User{" +
                  "id=" + id +
                  ", name='" + name + '\'' +
                  '}';
      }
  

• sql语句
  

• Mapper.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="com.harbin.dao.CarMapper">
      <resultMap id="CarResultMap" type="car">
          <id property="id" column="id"></id>
          <result property="name" column="name"></result>
          <result property="uId" column="uId"></result>
          <!--一对一关系：property值是类Car中的user字段
          			  javaType是字段对象的类型-->
          <association property="user" javaType="user">
              <id property="id" column="uId"></id>
              <result property="name" column="uname"></result>
          </association>
      </resultMap>
      <!--List<Car> find()-->
      <select id="find" resultMap="CarResultMap">
          select car.*,user.name uname from user,car where user.id = car.uId
      </select>
  </mapper>
  

• pojo

  public class User implements Serializable {
        
        
      private Integer id;
      private String name;
  
      List<Car> cars;
  
      public List<Car> getCars() {
        
        
          return cars;
      }
  
      public void setCars(List<Car> cars) {
        
        
          this.cars = cars;
      }
  
      public Integer getId() {
        
        
          return id;
      }
  
      public void setId(Integer id) {
        
        
          this.id = id;
      }
  
      public String getName() {
        
        
          return name;
      }
  
      public void setName(String name) {
        
        
          this.name = name;
      }
  
      @Override
      public String toString() {
        
        
          return "User{" +
                  "id=" + id +
                  ", name='" + name + '\'' +
                  '}';
      }
  }
  

  public class Car implements Serializable {
        
        
      private Integer id;
      private String name;
      private Integer uId;
  
      public Integer getId() {
        
        
          return id;
      }
  
      public void setId(Integer id) {
        
        
          this.id = id;
      }
  
      public String getName() {
        
        
          return name;
      }
  
      public void setName(String name) {
        
        
          this.name = name;
      }
  
      public Integer getuId() {
        
        
          return uId;
      }
  
      public void setuId(Integer uId) {
        
        
          this.uId = uId;
      }
  
      @Override
      public String toString() {
        
        
          return "Car{" +
                  "id=" + id +
                  ", name='" + name + '\'' +
                  ", uId=" + uId +
                  '}';
      }
  }
  
  

• sql语句
  

• Mapper.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="com.harbin.dao.UserMapper">
      <resultMap id="UserResultMap" type="user">
          <id property="id" column="uId"></id>
          <result property="name" column="uname"></result>
          <!--一对多关系：property值是类User中的cars字段
          			  ofType是集合中元素的类型-->
          <collection property="cars" ofType="car">
              <id property="id" column="id"></id>
              <result property="name" column="name"></result>
              <result property="uId" column="uId"></result>
          </collection>
      </resultMap>
      <!--List<User> find()-->
      <select id="find" resultMap="UserResultMap">
          select car.*,user.name uname from user LEFT JOIN car on user.id = car.uid
      </select>
  </mapper>