初识Mybatis一些总结

DBUtils 要设置为单例模式 

public enum DBUtil {

	INSTANCE;
	
	
	private SqlSessionFactory sessionFactory;
	
	private DBUtil() {
		
		String resource = "mybatis-config.xml";
		
		try (Reader reader = Resources.getResourceAsReader(resource)){

			sessionFactory = new SqlSessionFactoryBuilder().build(reader);
			
		} catch (IOException e) {

			e.printStackTrace();
		}
	}

	public SqlSessionFactory getSessionFactory() {
		return sessionFactory;
	}
}　

1 有关配置(mybatis-config.xml 文件)

 <?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>
<!-- 这个要注意是要放在typeAliases标签的前面  不然会报错-->

    <settings>
          <!-- 开启数据库下划线命名方式和 java 驼峰命名方式之间的转换 -->
          <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>

    <typeAliases>
        <!-- 设置别名，使用别名代替原始的名字 -->
        <typeAlias type="com.rjxy.model.User" alias="_User"/>
    </typeAliases>

	<environments default="development">
		<environment id="development">
			<transactionManager type="JDBC" />
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.jdbc.Driver" />
				<property name="url" value="jdbc:mysql://localhost:3306/数据库名" />
				<property name="username" value="root" />
				<property name="password" value="123456" />
			</dataSource>
		</environment>
	</environments>
	<mappers>
	
	    <!-- 使用 xml 的方式配置 -->  <!-- 这个是常用的方法 -->
		<mapper resource="UserMapper.xml" />  <!--这个对应另一个类的Mapper-->
		
		<!-- 使用注解的方式配置 -->
		<mapper class="com.rjxy.dao.CategoryDao"/>
	</mappers>
</configuration>

2  有关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="com.rjxy.dao.UserDao">

    <insert id="saveUser" parameterType="_User">
        insert into user(username, password, email) values (#{username}, #{password}, #{email})
    </insert>
    
    <select id="listUser" resultType="_User">
        select * from user
    </select>

</mapper>

3  注解的方式配置 , 不需要 CategoryMapper.xml    (但是不常用 ,  不方便)  对应上面相同颜色

4  模糊查询 , 如果有多个传参数模糊查询

 总共有三种方法:

1. 封装为对象
2. 使用 HashMap
3. 使用参数索引：
arg0，arg1，...
param1，param2，...

select * from user where username like #{value}

listUserByKey("%人%");

<select id="listUserByName" parameterType="String" resultType="_User">
        select * from user where username like '%${value}%'
</select>

dao.listUserByKey("人");

<select id="listUserByNameOrEmail" resultType="_User">
        select * from user where username like #{param1} or email like #{param2}
</select>


<select id="listUserByNameOrEmail" resultType="_User">
        select * from user where username like #{arg0} or email like #{arg1}
</select>

dao.listUserByNameOrEmail("%a%", "%q%");