Mapper动态代理

小咪咪 2021-09-19 04:24 336阅读 0赞

**目录**

1.通过id查询记录（SELECT \* FROM user WHERE id =\#\{id\}）

2.通过名字模糊查询用户列表（SELECT \* FROM user WHERE username like "%"\#\{name\}"%"）

3.查询记录数量（SELECT count(\*) from user）

4.手动映射（此时要用resultMap,而不是resultType了）-模糊查询

--------------------

# 1.通过id查询记录（SELECT \* FROM user WHERE id =\#\{id\}） #

![20190430204300239.png][]

User.java:

package com.sikiedu.bean;
    
    public class User {
    	private Integer id;
    	private String username;
    	private String password;
    	
    	public Integer getId() {
    		return id;
    	}
    	public void setId(Integer id) {
    		this.id = id;
    	}
    	public String getUsername() {
    		return username;
    	}
    	public void setUsername(String username) {
    		this.username = username;
    	}
    	public String getPassword() {
    		return password;
    	}
    	public void setPassword(String password) {
    		this.password = password;
    	}
    	
    	@Override
    	public String toString() {
    		return "User [id=" + id + ", username=" + username + ", password=" + password + "]";
    	}
    	
    	
    }

UserMapper.java:

package mapper;
    
    import com.sikiedu.bean.User;
    
    public interface UserMapper {
    
    	public User selectUserById(Integer id);
    }

UserMapper.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="mapper.UserMapper">
     
    	<select id="selectUserById" parameterType="Integer" resultType="com.sikiedu.bean.User">
    		SELECT * FROM user WHERE id =#{id}
    	</select>
    </mapper>

MapperTest.java:

package test;
    
    import java.io.IOException;
    import java.io.InputStream;
    
    import org.apache.ibatis.io.Resources;
    import org.apache.ibatis.session.SqlSession;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.apache.ibatis.session.SqlSessionFactoryBuilder;
    import org.junit.Test;
    
    import com.sikiedu.bean.User;
    
    import mapper.UserMapper;
    
    public class MapperTest {
    
    	@Test
    	public void Test() throws IOException{
    		String resource="sqlMapConfig.xml";
    		InputStream in = Resources.getResourceAsStream(resource);
    		SqlSessionFactoryBuilder ssfb=new SqlSessionFactoryBuilder();
    		SqlSessionFactory ssf=ssfb.build(in);
    		SqlSession session  = ssf.openSession();
    		
    		UserMapper mapper = session.getMapper(UserMapper.class);
    		User user = mapper.selectUserById(1);
    		System.out.println(user);
    
    	}
    }

运行结果：

![20190430204444961.png][]

# 2.通过名字模糊查询用户列表（SELECT \* FROM user WHERE username like "%"\#\{name\}"%"） #

MapperTest.java:

@Test
    	public void Test2() throws IOException{
    		String resource="sqlMapConfig.xml";
    		InputStream in = Resources.getResourceAsStream(resource);
    		SqlSessionFactoryBuilder ssfb=new SqlSessionFactoryBuilder();
    		SqlSessionFactory ssf=ssfb.build(in);
    		SqlSession session  = ssf.openSession();
    		
    		UserMapper mapper = session.getMapper(UserMapper.class);
    		List<User> user = mapper.selectUserByName("李");
    		for (User u : user) {
    			System.out.println(u);
    		}
    	}

UserMapper.java:

package mapper;
    
    
    import java.util.List;
    
    import com.sikiedu.bean.User;
    
    public interface UserMapper {
    
    //	public User selectUserById(Integer id);
    	
    	public List<User> selectUserByName(String name);
    }

UserMapper.xml:

<select id="selectUserByName" parameterType="String" resultType="com.sikiedu.bean.User">
    
    			SELECT * FROM user WHERE username like "%"#{name}"%"
    	</select>

运行结果：

![20190430205548239.png][]

# 3.查询记录数量（SELECT count(\*) from user） #

MapperTest.java:

@Test
    	public void Test4() throws Exception{
    		String resource="sqlMapConfig.xml";
    		InputStream in = Resources.getResourceAsStream(resource);
    		SqlSessionFactoryBuilder ssfb=new SqlSessionFactoryBuilder();
    		SqlSessionFactory ssf=ssfb.build(in);
    		SqlSession session  = ssf.openSession();
    		
    		UserMapper mapper = session.getMapper(UserMapper.class);
    		Integer count = mapper.selectUserCount();
    		System.out.println(count);
    	}

UserMapper.java:

public Integer selectUserCount();

UserMapper.xml:

<select id="selectUserCount" resultType="Integer">
    		SELECT count(*) from user
    	</select>

运行结果：

![20190501095531847.png][]

# 4.手动映射（此时要用resultMap,而不是resultType了）-模糊查询 #

如果数据库中每列的字段名和bean中对象中的属性名相同，那么系统会自动映射，此时可以使用resultType。

如果数据库中某列的字段名和bean中对象中的属性名不同，那么系统不会自动映射该属性，此时就不能使用resultType了，此时给该属性使用resultMap来手动映射就可以了。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMzIzMjU2_size_16_color_FFFFFF_t_70][]

User2.java:

package com.sikiedu.bean;
    
    public class User2 {
    
    	private Integer id;
    	private String u_username;//此属性名和数据库中的字段名不相同，需手动映射
    	private String password;
    	public Integer getId() {
    		return id;
    	}
    	public void setId(Integer id) {
    		this.id = id;
    	}
    	public String getU_username() {
    		return u_username;
    	}
    	public void setU_username(String u_username) {
    		this.u_username = u_username;
    	}
    	public String getPassword() {
    		return password;
    	}
    	public void setPassword(String password) {
    		this.password = password;
    	}
    	@Override
    	public String toString() {
    		return "User2 [id=" + id + ", u_username=" + u_username + ", password=" + password + "]";
    	}
    	
    	
    }

User2Mapper.java:

package com.sikiedu.mapper;
    
    import java.util.List;
    
    import com.sikiedu.bean.User2;
    
    public interface User2Mapper {
    
    	public List<User2> selectUserByName(String name);
    }

User2Mapper.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.sikiedu.mapper.User2Mapper">
    
    	<resultMap type="com.sikiedu.bean.User2" id="user2">
    		<result property="u_username" column="username"/>
    	</resultMap>
    	<select id="selectUserByName" resultMap="user2">
    
    			SELECT * FROM user WHERE username like "%"#{name}"%"
    	</select>
    
    </mapper>

Mapper2Test.java:

package test;
    
    import java.io.InputStream;
    import java.util.List;
    
    import org.apache.ibatis.io.Resources;
    import org.apache.ibatis.session.SqlSession;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.apache.ibatis.session.SqlSessionFactoryBuilder;
    import org.junit.Test;
    
    import com.sikiedu.bean.User2;
    import com.sikiedu.mapper.User2Mapper;
    
    public class Mapper2Test {
    
    	@Test
    	public void Test() throws Exception{
    		String resource="sqlMapConfig.xml";
    		InputStream in = Resources.getResourceAsStream(resource);
    		SqlSessionFactoryBuilder ssfb=new SqlSessionFactoryBuilder();
    		SqlSessionFactory ssf=ssfb.build(in);
    		SqlSession session  = ssf.openSession();
    		
    		User2Mapper mapper = session.getMapper(User2Mapper.class);
    		
    		List<User2> user = mapper.selectUserByName("李");
    		for (User2 u : user) {
    			System.out.println(u);
    		}
    	}
    }

运行结果：

![20190501101841418.png][]

[20190430204300239.png]: /images/20210725/cef5c766dd35481faa39756ccf488b5b.png
[20190430204444961.png]: /images/20210725/0032f80b1d6540cdbc8fbfcb11961ff2.png
[20190430205548239.png]: /images/20210725/e2fd1498beb64e88a812a856df0eb347.png
[20190501095531847.png]: /images/20210725/b0d489a798bd4b5fabc8969b0fe870da.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMzIzMjU2_size_16_color_FFFFFF_t_70]: /images/20210725/3f79a7eebeb546e8a7aa432a79ff98e7.png
[20190501101841418.png]: /images/20210725/b7b39e3df8db45c4bc88be7d032f2216.png