mybatis - 4. Mybatis基本应用 - 《Java 框架》

步骤
传统的dao层开发方式
代理开发方式
mybatis核心配置文件的参数详解
动态sql编写
复杂映射的开发
- 一对一查询
- 一对多查询

步骤

引入mybatis依赖 ```xml org.mybatis mybatis 3.4.5

mysql mysql-connector-java 5.1.6

junit junit 4.12


2. 编写实体类
3. 编写映射文件UserMapper.xml
```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.lagou.entity.User">
    <select id="findAll" resultType="com.lagou.entity.User">
        select * from user
    </select>
</mapper>

编写核心配置类sqlMapper.xml

<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
 <!--environments：运行环境-->
 <environments default="development">
     <environment id="development">
         <!--当前事务交由JDBC管理-->
         <transactionManager type="JDBC"/>
         <!--使用mybatis提供的连接池-->
         <dataSource type="POOLED">
             <property name="driver" value="com.mysql.jdbc.Driver"/>
             <property name="url" value="jdbc:mysql://localhost:3307/layui?characterEncoding=utf-8"/>
             <property name="username" value="root"/>
             <property name="password" value="root"/>
         </dataSource>
     </environment>
 </environments>
 <mappers>
     <mapper resource="UserMapper.xml"/>
 </mappers>
</configuration>

测试类

@Test
public void test1() throws IOException {
 InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
 SqlSessionFactory build = new SqlSessionFactoryBuilder().build(resourceAsStream);
 SqlSession sqlSession = build.openSession();
 List<User> users = sqlSession.selectList("com.lagou.entity.User.findAll");
 System.out.println(users);
 sqlSession.close();
}

传统的dao层开发方式

编写Dao接口

public interface UserDao {
 List<User> findAll() throws IOException;
}

编写Dao实现类

public class UserDaoImpl implements UserDao{
 @Override
 public List<User> findAll() throws IOException {
     InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
     SqlSessionFactory build = new SqlSessionFactoryBuilder().build(resourceAsStream);
     SqlSession sqlSession = build.openSession();
     List<User> users = sqlSession.selectList("com.lagou.entity.User.findAll");
     System.out.println(users);
     sqlSession.close();
     return users;
 }
}

测试
```
@Test
public void test2() throws IOException {
 UserDaoImpl userDao = new UserDaoImpl();
 List<User> all = userDao.findAll();
 System.out.println(all);
}
```
代理开发方式
Mapper接口开发方法只需要程序员编写Mapper接口，由Myabtis开发框架根据接口定义创建接口的动态代理对象，代理对象的方法体同上边Dao接口实现类方法。
Mapper接口需要遵循以下规范：
Mapper.xml文件中的namespace与mapper接口的全限定类名相同
Mapper接口的方法名和Mapper.xml定义的每个statement的id相同
Mapper接口的输入参数类型和mapper.xml定义的每个parameterType相同
Mapper接口的输出参数类型和mapper.xml定义的resultType类型相同

测试：

@Test
public void test3() throws IOException {
 InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
 SqlSessionFactory build = new SqlSessionFactoryBuilder().build(resourceAsStream);
 SqlSession sqlSession = build.openSession();
 UserDao mapper = sqlSession.getMapper(UserDao.class);
 List<User> all = mapper.findAll();
 System.out.println(all);
}

mybatis核心配置文件的参数详解

核心配置类sqlMapper.xml

<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
 <!--加载外部properties文件,可以更方便管理数据源参数-->
 <properties resource="jdbc.properties"/>
 <!--给实体类的全限定类名取别名-->
 <!--基本类型的别名mybatis已经配置好：int,string,long,double,boolean...-->
 <typeAliases>
     <!--给单独的实体取别名-->
     <typeAlias type="com.lagou.entity.User" alias="user"/>
     <!--批量取别名：就是该包下实体本身的类名,别名不区分大小写-->
     <package name="com.lagou.entity"/>
 </typeAliases>
 <!--environments：运行环境-->
 <environments default="development">
     <environment id="development">
         <!--当前事务交由JDBC管理-->
         <transactionManager type="JDBC"/>
         <!--使用mybatis提供的连接池-->
         <dataSource type="POOLED">
             <property name="driver" value="${jdbc.driver}"/>
             <property name="url" value="${jdbc.url}"/>
             <property name="username" value="${jdbc.username}"/>
             <property name="password" value="${jdbc.password}"/>
         </dataSource>
     </environment>
 </environments>
 <mappers>
     <mapper resource="UserMapper.xml"/>
 </mappers>   
</configuration>

外部配置文件jdbc.propertice

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3307/layui?characterEncoding=utf-8
jdbc.username=root
jdbc.password=root

动态sql编写

多条件查询if

<?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.lagou.entity.dao.UserDao">
 <!--多条件组合查询，演示if-->
 <select id="findByCondition" resultType="com.lagou.entity.User" parameterType="com.lagou.entity.User">
     select * from user
     <where>
         <if test="id != null and id != ''">
             and id=#{id}
         </if>
         <if test="name != null and name != ''">
             and name = #{name}
         </if>
     </where>
 </select>
</mapper>

多值查询foreach

<select id="findByIds" resultType="com.lagou.entity.User">
 select * from user
 <where>
     <foreach collection="array" open="id in (" close=")" separator="," item="id">
         #{id}
     </foreach>
 </where>
</select>

抽取sql

<sql id="selectUser">
    select * from user
</sql>
<select id="findAll" resultType="com.lagou.entity.User">
    <include refid="selectUser"></include>
</select>

复杂映射的开发

一对一查询

user类

public class User {
 private Long id;
 private String name;
 private List<Order> orderList;
}

order类

public class Order {
 private Integer orderId;
 private String name;
 private User user;
}

查询语句

<?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.lagou.entity.dao.OrderDao">
 <resultMap id="OrderMap" type="com.lagou.entity.Order">
     <result property="orderId" column="order_id"/>
     <result property="name" column="name"/>
     <!--order类里的封装的user类-->
     <association property="user" javaType="com.lagou.entity.User">
         <result property="id" column="id"/>
         <result property="name" column="name"/>
     </association>
 </resultMap>
 <select id="findOrderAndUser" resultMap="OrderMap">
     SELECT * FROM `order` o,`user` u WHERE o.user_id = u.id
 </select>
</mapper>

一对多查询

```xml

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### 多对多查询
```xml
<resultMap id="roleMap" type="com.lagou.entity.User">
  <id property="id" column="uid"/>
  <result property="name" column="name"/>
  <!--user类里面封装的order集合类-->
  <collection property="roleList" ofType="com.lagou.entity.Role">
    <id property="rid" column="rid"/>
    <result property="rname" column="rname"/>
  </collection>
</resultMap>
<select id="findAllRole" resultMap="roleMap">
  SELECT * FROM `user` u LEFT JOIN `user_role` ur ON u.id = ur.uid LEFT JOIN `role` r ON         r.rid = ur.rid
</select>

4. Mybatis基本应用

步骤

传统的dao层开发方式

代理开发方式

mybatis核心配置文件的参数详解

动态sql编写

复杂映射的开发

一对一查询

一对多查询