Nine, mybaitis learning - parameter processing

Single parameter: directly use #{parameter name} to obtain the value, mybatis does not do special processing, and the parameter name can be written casually.
Multiple parameters: use #{param1}, #{param2} value, or #{args1} #{args2}
Named parameters: explicitly specify the key in the encapsulation map through @param("key"), and you can retrieve the parameter value through #{key}
POJO: If multiple parameters happen to be business models, the business model can be passed in at this time, and the value can be obtained through #{attribute name}
Map: If multiple parameters are not business models and are not frequently used, you can customize the Map to pass in
TO: If multiple parameters are not business models and are often used, you can customize a TO to transfer objects

1. A single parameter

In the configuration sql mapping file, when a parameter is passed in the sql statement, how should it be passed?

Earlier we tested that mybatis does not do special processing, just use #{parameter name} to take out the parameter value.
Note: In fact, here #{id}, the parameter name id can write any value, because only one parameter is passed. .



<?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.pjf.mybatis.dao.HotelMapper">
    <!-- public Hotel getHotel(Integer i); -->
    <select id="getHotel" resultType="com.pjf.mybatis.po.Hotel">
        select id,hotel_name as
        hotelName, hotel_address as hotelAddress, price from hotel
        where
     <!-- 这里#{id}可以写成任何值如 #{abc}-->
        id=#{id} 
    </select>
</mapper>

2. Multiple parameters

First of all, let’s take an example. Of course, it’s easy to think that this is the way to get parameter values and write #{id} and #{price} directly.


<?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.pjf.mybatis.dao.HotelMapper">
    <!-- public Hotel getHotel(Integer i,Integer j); -->
    <select id="getHotel" resultType="com.pjf.mybatis.po.Hotel">
        select id,hotel_name as
        hotelName, hotel_address as hotelAddress, price from hotel
        where
        id=#{id} and price =#{price}
    </select>
</mapper>

This is wrong, after running it, I found an error

Caused by: org.apache.ibatis.binding.BindingException: 
Parameter 'id' not found. 
Available parameters are [arg1, arg0, param1, param2]

In fact, when there are multiple parameters, mybatis will do special processing, and multiple parameters will be encapsulated as map

key is param1, param2.....or 0, 1, 2 index value

value is the parameter value

You can experiment again and change the parameter name to #{param1},#{ param2}



<?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.pjf.mybatis.dao.HotelMapper">
    <!-- public Hotel getHotel(Integer i,Integer j); -->
    <select id="getHotel" resultType="com.pjf.mybatis.po.Hotel">
        select id,hotel_name as
        hotelName, hotel_address as hotelAddress, price from hotel
        where
        id=#{param1} and price =#{param2}
    </select>
</mapper>

It can be found that the result is correct at this time

3. Named parameters

In fact, people are still used to using #{id} and #{price} instead of #{param1} and #{param2}, of course mybatis also provides a solution

By explicitly specifying the key in the encapsulated map by @param("key"), the parameter value can be retrieved by #{key}

@param("key") is written on the hotelMapper interface



package com.pjf.mybatis.dao;

import org.apache.ibatis.annotations.Param;

import com.pjf.mybatis.po.Hotel;

public interface HotelMapper {

    public Hotel getHotel(@Param("id")Integer i,@Param("price")Integer j);

}



hotelMapper.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.pjf.mybatis.dao.HotelMapper">
    <!-- public Hotel getHotel(@Param("id")Integer i,@Param("price")Integer j); -->
    <select id="getHotel" resultType="com.pjf.mybatis.po.Hotel">
        select id,hotel_name as
        hotelName, hotel_address as hotelAddress, price from hotel
        where
        id=#{id} and price =#{price}
    </select>
</mapper>

At this time, you can get the parameter value through #{id} and #{price}.

4、map

The above is @param("key") to specify a key, then of course we can also pass in a Map ourselves.


实例：

hotelMapper接口


package com.pjf.mybatis.dao;

import java.util.Map;
import org.apache.ibatis.annotations.Param;
import com.pjf.mybatis.po.Hotel;

public interface HotelMapper {

    public Hotel getHotel(Map<String,Integer> map);

}



hotelMapper.xml和上面一样


<?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.pjf.mybatis.dao.HotelMapper">
    <!-- public Hotel getHotel(@Param("id")Integer i,@Param("price")Integer j); -->
    <select id="getHotel" resultType="com.pjf.mybatis.po.Hotel">
        select id,hotel_name as
        hotelName, hotel_address as hotelAddress, price from hotel
        where
        id=#{id} and price =#{price}
    </select>
</mapper>

public class TestHotel {

    public SqlSessionFactory sqlSessionFactory() throws IOException {
        // mybatis的配置文件
        String resource = "mybatis_config.xml";
        // 使用类加载器加载mybatis的配置文件（它也加载关联的映射文件）TestHotel.class.getClassLoader()
        InputStream is = Resources.getResourceAsStream(resource);
        // 构建sqlSession的工厂
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
        return sessionFactory;
    }

    // 查
    @Test
    public void getHotel() throws IOException {

        SqlSessionFactory sessionFactory = sqlSessionFactory();
        SqlSession session = sessionFactory.openSession();
        HotelMapper hotelMapper = session.getMapper(HotelMapper.class);
        System.out.println(hotelMapper.getClass());
        //手动封装一个map传入
        Map map =new HashMap<>();
        map.put("id", 1001);
        map.put("price", 997);
        Hotel hotel = hotelMapper.getHotel(map);
        System.out.println(hotel);
        session.close();
    }
}

5. Object parameters (POJO)

If multiple parameters happen to be business models, then you can directly pass them as objects, and you can get the attribute values of the object through #{attribute value}

hotelMapper接口

package com.pjf.mybatis.dao;

import java.util.Map;
import org.apache.ibatis.annotations.Param;
import com.pjf.mybatis.po.Hotel;

public interface HotelMapper {
    public Hotel getHotel(Map<String,Integer> map);

 //直接传入hotel业务模型
    public void insertHotel(Hotel hotel);
}

6. Object parameters (TO)

If multiple parameters are not business models, but are useful more frequently, we can write a TO object specifically to pass parameters

“`
package com.pjf.mybatis.po;

public class HotelTo {

private int id;
private int price;

public int getId() {
    return id;
}

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

public int getPrice() {
    return price;
}

public void setPrice(int price) {
    this.price = price;
}

}
package com.pjf.mybatis.dao;

import java.util.Map;
import org.apache.ibatis.annotations.Param;
import com.pjf.mybatis.po.Hotel;

public interface HotelMapper {
public Hotel getHotel(Map