初識Mybatis一些總結

DBUtils 要設置爲單例模式 

 

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 有關配置(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>
<!-- 這個要注意是要放在typeAliases標籤的前面  否則會報錯-->

    <settings> <!-- 開啓數據庫下劃線命名方式和 java 駝峯命名方式之間的轉換 --> <setting name="mapUnderscoreToCamelCase" value="true"/> </settings>

    <typeAliases> <!-- 設置別名，使用別名代替原始的名字 --> <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/數據庫名" />
				<property name="username" value="root" />
				<property name="password" value="123456" />
			</dataSource>
		</environment>
	</environments>
	<mappers>
	
	    <!-- 使用 xml 的方式配置 -->  <!-- 這個是經常使用的方法 -->
		<mapper resource="UserMapper.xml" /> <!--這個對應另外一個類的Mapper-->
		
		<!-- 使用註解的方式配置 -->
		<mapper class="com.rjxy.dao.CategoryDao"/>
	</mappers>
</configuration>

2  有關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  註解的方式配置 , 不須要 CategoryMapper.xml    (可是不經常使用 ,  不方便)  對應上面相同顏色

4  模糊查詢 , 若是有多個傳參數模糊查詢

 總共有三種方法:

1. 封裝爲對象
2. 使用 HashMap
3. 使用參數索引：
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%");