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MyBatis三个查询方法_selectList_selectOne_selectMap

分类: 文章 • 2025-05-02 11:46:46

一、项目的目录结构：

MyBatis三个查询方法_selectList_selectOne_selectMap

二、回顾Mybatis的项目搭建步骤

1、导入相关的包(11个jar包)1
2、在src目录下编写编写配置文件（mybatis-cfg.xml）
3、编写实体类(User.java)
4、编写映射文件（UserMapper.xml）
5、编写测试文件
6、调用JUnit 5进行调试

相关jar包截图

MyBatis三个查询方法_selectList_selectOne_selectMap

mybatis-cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-config.dtd">
  
  <configuration>
  	<environments default="dev">
  		<environment id="dev">
  			<transactionManager type="JDBC" />
  				<dataSource type="POOLED">
  				
  				<property name="driver" value="com.mysql.jdbc.Driver"/>
 				<property name="url" value="jdbc:mysql://localhost:3306/java505"/>
 				<property name="username" value="root"/>
 				<property name="password" value="szxy"/>
  				</dataSource>
  		</environment>
  		
  	</environments>
  	<mappers>
  	   <mapper resource="cn/bjsxt/mapper/usermapper.xml"/>
  	</mappers>
  </configuration>

注：java505为mysql下的数据库名。驱动器driver的值不能更改。

实体类：

设置私有变量，
实现序列化，
带参无参构造函数，
取值赋值方法，
改写toString方法，
hashCode（）和equals（）方法。

package cn.bjsxt.pojo;

import java.io.Serializable;

public class User implements Serializable{
	private int id;
	private String name;
	private String password;
	
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}
	public User(int id, String name, String password) {
		super();
		this.id = id;
		this.name = name;
		this.password = password;
	}
	public User() {
		super();
	}
	@Override
	public String toString() {
		return "User [id=" + id + ", name=" + name + ", password=" + password + "]";
	}
	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + id;
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		result = prime * result + ((password == null) ? 0 : password.hashCode());
		return result;
	}
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		User other = (User) obj;
		if (id != other.id)
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		if (password == null) {
			if (other.password != null)
				return false;
		} else if (!password.equals(other.password))
			return false;
		return true;
	}
	
	
}

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="cn.bjsxt.mapper.UserMapper">
	<select id="selAll" resultType="cn.bjsxt.pojo.User">
		select * from t_user
	</select>  	
	<select id="selOne" resultType="cn.bjsxt.pojo.User">
		select * from t_user where id=1
	</select>  
  </mapper>

select id=“selAll”: 定义查询方法的名称
select * from t_user：SQL语句为具体操作的内容

测试类testSelect.java

package cn.bjsxt.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import java.util.Map;
import java.util.Set;

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 cn.bjsxt.pojo.User;

public class TestSelect {
	@Test
	public void testSelectList() throws IOException {
		InputStream is = Resources.getResourceAsStream("mybatis-cfg.xml");
		SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is);
		SqlSession session = factory.openSession();
		
		/**List<User> list = session.selectList("cn.bjsxt.mapper.UserMapper.selAll");
		for (User user : list) {
			System.out.println(user);
		}*/
		
		/**User user = session.selectOne("cn.bjsxt.mapper.UserMapper.selOne");
		System.out.println(user);*/
		
		Map<Integer, User> map = session.selectMap("cn.bjsxt.mapper.UserMapper.selAll", "id");
		System.out.println(map);
		Set<Integer> set = map.keySet();
		for (Integer k : set) {
			System.out.println(map.get(k));
		}
		
		session.close();
	}
}

注：1、使用Junit 5需要在类里面添加一段代码@Test，并导入import org.junit.Test;
2、selectAll查询的是所有对象，selectOne查询的是一个对象并且需要设置条件，selectMap查询的是具有键值关系的对象

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