mybatisDay1
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在MyBatis框架的学习中,"mybatisDay1"涵盖了几个关键知识点,这些知识点对于理解和应用MyBatis至关重要。下面将详细阐述这些概念。 1. 占位符与拼接符的使用: MyBatis允许我们在SQL语句中使用占位符来防止SQL注入,提高代码可读性和安全性。通常我们使用`?`作为占位符,例如: ```sql SELECT * FROM users WHERE id = ? ``` 在Java代码中,对应的参数会被传入到PreparedStatement对象中,确保安全执行。同时,MyBatis还支持拼接符如`#{}`,它不仅可以防止SQL注入,还能提供字段名和表名的自动转义。 2. Insert语句自增主键返回值: 当表中的主键是自增类型时,MyBatis提供了获取插入后自增主键值的方法。通过在`<selectKey>`标签中配置,可以在插入数据后获取新生成的主键。例如: ```xml <insert id="insertUser"> INSERT INTO users(name, email) VALUES(#{name}, #{email}) <selectKey keyProperty="id" resultType="int" order="AFTER"> SELECT LAST_INSERT_ID() </selectKey> </insert> ``` 这样,插入后,主键ID会自动赋值给Java对象的相应属性。 3. Mapper动态代理开发方式: MyBatis的Mapper接口可以使用动态代理实现,使得我们可以直接调用方法来执行SQL。首先定义一个Mapper接口,然后在Mapper XML文件中编写SQL,MyBatis会自动生成这个接口的实现类。例如: ```java public interface UserMapper { void insertUser(User user); } ``` 在运行时,MyBatis会创建UserMapper的动态代理实例,当我们调用`insertUser()`方法时,实际上执行的是XML文件中对应的SQL。 4. Mapper映射器的三种方式: - XML配置文件:这是最传统的方式,将SQL语句写在Mapper XML文件中,与对应的Mapper接口结合使用。 - 注解方式:可以直接在Mapper接口的方法上使用注解来编写SQL,简洁明了,但可能造成代码过于分散。 - 动态SQL:MyBatis的动态SQL功能允许在XML或注解中使用条件判断、循环等,构建灵活的SQL语句。 理解并掌握这些MyBatis的基础知识,能够帮助开发者高效地操作数据库,实现业务逻辑。在实际项目开发中,根据需求选择合适的Mapper开发方式,合理利用占位符和拼接符,以及正确处理自增主键的返回值,都是提升代码质量的关键。在深入学习MyBatis的过程中,还可以探索更高级的特性,如结果映射、缓存机制、事务管理等,进一步提升开发效率。
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