mybatis（一）

项目目录

1.两个配置文件

全局配置文件mybatis-config.xml

在配置数据源时将数据库配置写在jdbc.properties中

jdbc.properties

driverClass=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/testdemo
username=root
password=root

mybatis-config.xml

五个部分

1.读取jdbc.properties资源文件

2.配置jdbc数据源

3.mapper.xml配置文件路径，告诉mybatis去哪里找sql语句

4.如果数据库字段和实体类字段不同，且数据库字段符合驼峰命名格式则可开启驼峰命名转换

5.在mapper.xml里可以不用写实体类的全类名，只需写实体类类名，用来减少类完全限定名的冗余

<?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>
	<!-- 加载jdbc的配置文件 -->
	<properties resource="jdbc.properties"></properties>
	<!-- 驼峰命名转换 -->
	<settings>
		<setting name="mapUnderscoreToCamelCase" value="true" />
	</settings>
	<!-- 为java类型命名的一个短名字在mapperxml里面可以只用类名 -->
	<typeAliases>
		<typeAlias alias="Role" type="com.hwj.pojo.Role" />
	</typeAliases>
	<environments default="development">
		<environment id="development">
			<transactionManager type="JDBC" />
			<dataSource type="POOLED">
				<property name="driver" value="${driverClass}" />
				<property name="url" value="${url}" />
				<property name="username" value="${username}" />
				<property name="password" value="${password}" />
			</dataSource>
		</environment>
	</environments>
	<mappers>
		<mapper resource="com/hwj/mapper/roleMapper.xml" />
	</mappers>

</configuration>

 

mapper.xml映射文件

dao的实现类对sqlsession的使用方式很相似,mybatis接口实现了动态代理，不需要接口的实现类，

namespace的值需要和对应dao接口的全路径一致，dao层接口名称与sql定义的id一致，但本身如果有dao接口的实现类对namespace的定义是没有限制的

接口没有实现类所以需要特殊的实例化，通过sqlsession.getMapper(dao.class)获得

接口代码：

package com.hwj.dao;

import java.util.List;

import com.hwj.pojo.Role;

public interface IRole {
  public List<Role> selectAll();
  public Role selectById(Long id);
  public int delete(Long id);
  public int update(Role role);
  public int add(Role role);
}

mapper.xml代码

<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.hwj.dao.IRole">
	<select id="selectAll" resultType="Role">
		select * from role;
	</select>
	<select id="selectById" resultType="Role">
		select * from role where id=#{id}
	</select>
	<insert id="add" parameterType="Role">
		insert into role(role_name,description) values(#{roleName},#{description})
	</insert>
	<delete id="delete">
		delete from role where id=#{id}
	</delete>
	<update id="update" parameterType="Role">
	   update role set role_name=#{roleName},description=#{description} where id=#{id}
	</update>
</mapper>

#{} 存在mapper.xml中的sql语句部分，标识该位置可以接受参数信息。相当于?占位符。

测试类：

1.从xml中构建SqlSessionFactory

String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
	SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

2.从sqlSessionFactory得到SqlSession

SqlSession session = sqlSessionFactory.openSession();

3.实例化dao

IRole roledao=session.getMapper(IRole.class);

4.操作dao的方法

新增部分：多表查询，延迟加载

表：role user user_role

role                                                                        user

 

user-role

查询某个角色下所有的用户

Role类中有一个属性为List<User>多对一的关系

Role类：

package com.hwj.pojo;

import java.util.ArrayList;
import java.util.List;

public class Role {
	private Long id;
	private String roleName;
	private String description;
	private List<User> list;
	public Long getId() {
		return id;
	}
	public void setId(Long id) {
		this.id = id;
	}
	public String getRoleName() {
		return roleName;
	}
	public void setRoleName(String roleName) {
		this.roleName = roleName;
	}
	public String getDescription() {
		return description;
	}
	public void setDescription(String description) {
		this.description = description;
	}
	public List<User> getList() {
		return list;
	}
	public void setList(List<User> list) {
		this.list = list;
	}
	@Override
	public String toString() {
		return "Role [id=" + id + ", roleName=" + roleName + ", description=" + description + ", list=" + list + "]";
	}
	public Role(String roleName, String description) {
		this.roleName = roleName;
		this.description = description;
	}
	public Role(Long id, String roleName, String description) {
		
		this.id = id;
		this.roleName = roleName;
		this.description = description;
	}
	public Role() {
		
	}
	
	
}

mapper.xml中

<select id="selectT" resultType="User">
	   select u.* from user_role ur inner join user u on ur.user_id=u.id where ur.role_id=#{id};
	</select>
	<resultMap type="Role" id="result">
	   <id column="id" property="id"></id>
	   <result column="username"  javaType="String"  property="username"/>
	   <result column="password" javaType="String"   property="password"/>
	   <result column="create_time" javaType="Date"  property="createTime"/>
	   <collection property="list" javaType="list" ofType="User" autoMapping="true" select="selectT" column="id"></collection>
	</resultMap>
	<select id="selectTwo" resultMap="result">
	   select * from Role where id=#{id}
	</select>

selectTwo接口的返回值为Role