1. 快速使用
步骤:
1. 添加Mybatis依赖坐标。
2. 创建数据库实体表,准备数据。
3. 创建实体类。
4. 编写配置文件mybatis-config.xml
5. 编写映射文件XxxMapper.xml
6. 测试类测试
1. 添加Mybatis依赖坐标。
<!--mybatis依赖-->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.9</version>
</dependency>
<!--数据库依赖-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.16</version>
</dependency>
2. 数据库表
实体类
package pojo;
/**
* @Date: 2022/4/21 20:11
* @author: ZHX
* @Description: 实体类 User类
*/
public class User {
private int id;
private String username;
private String password;
public User() {
}
public User(int id, String username, String password) {
this.id = id;
this.username = username;
this.password = password;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", password='" + password + '\'' +
'}';
}
public int getId() {
return id;
}
public void setId(int 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;
}
}
mybatis-config.xml
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/xin?useSSL=false&characterEncoding=utf8&serverTimezone=UTC"/>
<property name="username" value="root"/>
<property name="password" value="123456"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="UserMapper.xml"/>
</mappers>
</configuration>
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="UserMapper">
<select id="findAll" resultType="pojo.User">
select *
from user
</select>
</mapper>
测试
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 pojo.User;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
/**
* @Date: 2022/4/25 14:42
* @author: ZHX
* @Description: 测试使用Mybatis框架简单查询
*/
public class Test {
public static void main(String[] args) throws IOException {
InputStream resource = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resource);
SqlSession sqlSession = sqlSessionFactory.openSession();
List<User> userList = sqlSession.selectList("UserMapper.findAll");
System.out.println(userList);
sqlSession.close();
}
}
2. mybatis-config.xml配置文件
常用配置
<?xml version="1.0" encoding="UTF-8" ?>
<!--xml文档版本，编码-->
<!--dtd约束-->
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--根标签-->
<configuration>
<!--properties:设置属性(键值对形式),在该配置文件中可以通过key使用value,用来替换需要动态配置的属性值-->
<!--方式一 引入外部文件-->
<properties resource="jdbc.properties"/>
<!--方式二 直接设置-->
<properties>
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/xin?useSSL=false&characterEncoding=utf8&serverTimezone=UTC"/>
<property name="username" value="root"/>
<property name="password" value="123456"/>
</properties>
<!--方式三 引入网络资源-->
<properties url="http://localhost:80/...."/>
<!--typeAliases:别名,在配置文件中设置的别名可以在mapper映射文件中使用-->
<typeAliases>
<!--方式一: 给某个类单独设置别名-->
<typeAlias type="pojo.User" alias="user"/>
<!--方式二:包扫描,给该包下的所有类设置别名,默认别名是类名首字母小写-->
<package name="pojo"/>
</typeAliases>
<!--environments:数据库环境，支持多环境.default选中该id的环境-->
<environments default="development">
<!--开发环境-->
<environment id="development">
<!--指定事务管理器的类型，JDBC、MANAGED-->
<!--JDBC:直接使用JDBC的提交和回滚操作-->
<!--MANAGED:从不提交或回滚，默认关闭-->
<transactionManager type="JDBC"/>
<!--指定数据源,POOLED、UNPOOLED、JNDI-->
<!--POOLED:使用数据库连接池-->
<!--UNPOOLED:不使用连接池，每次请求都要打开或关闭连接-->
<!--JNDI:这个数据源实现是为了能在如 EJB 或应用服务器这类容器中使用，容器可以集中或在外部配置数据源，然后放置一个 JNDI 上下文的数据源引用。-->
<dataSource type="POOLED">
<!--数据源的配置参数-->
<property name="driver" value="${driver}"/>
<property name="url" value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
<!--测试环境-->
<environment id="test">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${driver}"/>
<property name="url" value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<!--映射器,配置映射文件路径-->
<mappers>
<!--方式一:相对路径-->
<mapper resource="mapper/UserMapper.xml"/>
<!--方式二:使用资源定位符-->
<mapper url="file://mapper/UserMapper.xml"/>
<!--方式三:使用接口作为映射,有要求全限定名必须和XxxMapper.xml文件的namespace一致.-->
<mapper class="mapper.UserMapper"/>
<!--方式四:将包内的接口全部注册为映射器-->
<package name="mapper"/>
</mappers>
</configuration>
其他配置
3. XxxMapper.xml映射文件
常用配置
<?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:根标签, namespace属性: 唯一标识,区分mapper.xml文件，建议和dao接口对应:包名.接口名-->
<mapper namespace="mapper.UserMapper">
<!--查询-->
<select id="findAll" resultType="user">
select *
from user
</select>
<!--插入-->
<insert id="insert" parameterType="user">
# 类似与jdbc中的预编译sql写法:insert into user(id, username, password) values(?,?,?)
insert into user(id, username, password)
values (#{id}, #{username}, #{password})
</insert>
<!--更新-->
<update id="update" parameterType="user">
update user
set username = #{username},
password = #{password}
where id = #{id}
</update>
<!--删除-->
<delete id="deleteById" parameterType="int">
delete
from user
where id = #{id}
</delete>
<!--sql语句抽取-->
<sql id="selectUser">
select *
from user
</sql>
<!--动态sql-->
<!--if 多条件查询，不确定用户会用几个参数来查,所以null的字段不查-->
<!--<where>标签相当于自带个1=1,当if条件都不满足时，where 1=1-->
<select id="findByCondition" parameterType="user" resultType="user">
/*使用抽取的sql*/
<include refid="selectUser"/>
<where>
<if test="id!=0">
id =#{id}
</if>
<if test="username != null">
and username = #{username}
</if>
<if test="password != null">
and password = #{password}
</if>
</where>
</select>
<!--动态sql in-->
<select id="findByIds" parameterType="list" resultType="user">
select *
from user
<where>
<foreach collection="list" open="id in (" close=")" item="id" separator=",">
#{id}
</foreach>
</where>
</select>
</mapper>
其他配置
4. 多表操作
表与表的关系:
1.一对一:共用同一个主键或一个表的外键和另一个表的主键映射。
2.一对多或多对于:
3.多对多:
数据库实体表
订单表order
用户表user
4.1 一对一
sql参考
select *, a.id as oid, b.id as uid
from `order` a,
user b
where a.user_id = b.id;
<?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.OrderMapper">
<resultMap id="orderMap" type="pojo.Order">
<!--手动自定字段和实体属性的映射关系-->
<id column="oid" property="id"/>
<result column="order_time" property="orderTime"/>
<result column="total" property="total"/>
<!--Order对象中的user属性赋值-->
<!--方式一-->
<result column="uid" property="user.id"/>
<result column="username" property="user.username"/>
<result column="password" property="user.password"/>
<!--方式二-->
<association property="user" javaType="pojo.User">
<id column="uid" property="id"/>
<result column="username" property="username"/>
<result column="password" property="password"/>
</association>
</resultMap>
<!--多表查询-->
<!-- 查询该订单以及对应的用户信息。查询结果无法封装到匹配的实体类,用resultMap进行中间转换-->
<select id="findOrderAndUser" resultMap="orderMap">
select *, a.id as oid, b.id as uid
from `order` a,
user b
where a.user_id = b.id;
</select>
</mapper>
4.2 一对多
sql参考
select *, u.id as uid
from user u,
`order` o
where u.id = o.user_id;
<!--封装多表查询的结果-->
<resultMap id="userOrders" type="pojo.User">
<id column="uid" property="id"/>
<result column="username" property="username"/>
<result column="password" property="password"/>
<collection property="orderList" ofType="pojo.Order">
<id column="oid" property="id"/>
<result column="order_time" property="orderTime"/>
<result column="total" property="total"/>
</collection>
</resultMap>
<!--一对多,查询一个用户的所有订单-->
<select id="findUser" resultMap="userOrders">
select *, u.id as uid
from user u,
`order` o
where u.id = o.user_id;
</select>
4.3 多对多
一个用户有多个角色，一个角色属于多个用户。
表
<!--封装多表查询的结果-->
<resultMap id="userAndRole" type="pojo.User">
<id column="uid" property="id"/>
<result column="username" property="username"/>
<result column="password" property="password"/>
<collection property="roleList" ofType="pojo.Role">
<id column="rid" property="id"/>
<result column="role_description" property="description"/>
</collection>
</resultMap>
<!--多对多查询-->
<select id="findUserAndRole" resultMap="userAndRole">
select *
from user u,
role r,
user_role ur
where u.id = ur.uid
and r.id = ur.rid
</select>
