三 mybatis typeAlias（别名）使用和resultMap使用

 1、MyBatis提供的typeAlias

 

 2、定义自定义类型的别名

 定义自定义类型的别名

1.在mybatis-config.xml中增加

  <typeAliases>
      <typeAlias alias="user" type="cn.itcast.pojo.User"/>
  </typeAliases>

2.在UserMapper.xml中使用别名 resultType="user"

<select id="loadUserById" parameterType="integer" resultType="user">
      select * from user where id = #{id}
 </select>

 

 

3、resultMap使用

1.创建person表

  create table person(id int primary key,user_name varchar(50),age int,address varchar(150));
  desc person;
  insert into person values(1,’laozhao’,35,’haidian’);

2.创建person.java

public class Person {

  private Integer id;
  private String userName;
  private Integer age;
  private String address;

  set get ...

}

3.创建PersonMapper.xml

<mapper namespace="cn.itcast.dao.PersonMapper">
  <select id="loadPersonById" parameterType="integer" resultType="person">
      select * from person where id = #{id}
  </select>
</mapper>

4.修改mybatis-config.xml,增加person相关信息

<typeAliases>
    <typeAlias alias="person" type="cn.itcast.pojo.Person"/>
</typeAliases>
<mapper resource="cn/itcast/dao/PersonMapper.xml"/>

5.创建测试类TestPerson

@Test
public void testloadPersonById(){

    PersonMapper personMapper = sqlSession.getMapper(PersonMapper.class);
    Person person = sqlSession.selectOne("cn.itcast.dao.PersonMapper.loadPersonById", 1);
    System.out.println(person);
}

如何在javabean属性和表字段不一致的情况下正常取值？

 

方式一：查询语句中指定别名

1 <select id="loadPersonById2" parameterType="integer" resultType="person"> 2 3 　　select id,user_name as userName,age,address from person where id = #{id} 4 5 </select>

方式二、使用resultMap标签

 1 <resultMap type="person" id="personMap">  2  3 <result property=“userName" column="user_name"/>  4  5 </resultMap>  6  7 <select id="loadPersonById3" parameterType="integer" resultMap="personMap">  8  9 　　select * from person where id = #{id} 10 11 </select>

 

resultMap的使用  映射一对多、多对一

 

1.创建订单表orders

 create table orders(id int primary key,pid int,num varchar(12),name varchar(150),price double(10,2));

 desc orders;

 insert  orders values(1,1,'n101','shouji',1342.23);

 insert  orders values(2,1,'d102','diannao',8766.74);

 insert  orders values(3,1,'p103','pingban',3342.53);

2.创建orders.java

 public class Orders {

  private Integer id;

  private String num;

  private String name;

  private Double price;

  private Person person;

  get set ...

}

3.创建OrdersMapper.xml

<mapper namespace="cn.itcast.dao.OrdersMapper">

  <resultMap type="orders" id="ordersMap">

 　　 <result property="num" column="num"/>

  　　<result property="name" column="name"/>

  　　<association property="person" javaType="person" >

　　  　　<result property="name" column="user_name"/>

 　　 　　<result property="address" column="address"/>

  　　</association>

  </resultMap>

  <select id="loadOrdersById" parameterType="integer" resultMap="ordersMap">

  select a.*,b.* from orders a,person b where a.pid=b.id and a.id = #{id}

  </select>

</mapper>

4.修改mybatis-config.xml，增加

<typeAlias alias="orders" type="cn.itcast.pojo.Orders"/>
<typeAlias alias="persion" type="cn.itcast.pojo.Persion"/>
<mapper resource="cn/itcast/dao/OrdersMapper.xml"/>

5.创建TestOrders

public class TestOrders {

  @Test

  public void loadOrdersById(){

  Orders o = sqlSession.selectOne("cn.itcast.dao.OrdersMapper.loadOrdersById", 1);

  System.out.println("num:"+o.getNum() + ",name:" + o.getName() + ",personName:"

  + o.getPerson().getName() + ",address:" + o.getPerson().getAddress());

  }

}

1.在Person.java中增加对应订单的list

  private List<Orders> ordersList = new ArrayList<Orders>();

  public List<Orders> getOrdersList() {

  return ordersList;

  }

  public void setOrdersList(List<Orders> ordersList) {

  this.ordersList = ordersList;

  }

2.在PersonMapper.xml中增加查询

<resultMap type="person" id="personMap2">

 　<result property="name" column="user_name"/>

　　　　<!--配置orderList属性，并制定类型为orders-->
  <collection property="ordersList" javaType="orders">

  　　　　<result property="name" column="name"/>

 　　　　 <result property="price" column="price"/>

  　　　　<result property="num" column="num"/>

  </collection>

 </resultMap>

<select id="loadPersonById4" parameterType="integer" resultMap="personMap2">

  select a.*,b.* from person a,orders b where a.id=b.pid and a.id = #{id}

</select>

4. TestPerson中增加方法

@Test

  public void loadPersonById4(){


   Person person = sqlSession.selectOne("cn.itcast.dao.PersonMapper.loadPersonById4", 1);

   System.out.println(person.getName() + "  " + person.getOrdersList().size());

   for(Orders o: person.getOrdersList()){

  　　　　 System.out.println(o.getName() + "   " + o.getPrice() + "  " + o.getNum());

  }

  }