mybatis入门

mybatis01

MyBatis 是一款优秀的持久层框架，它支持定制化 SQL、存储过程以及高级映射。MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可以使用简单的 XML 或注解来配置和映射原生类型、接口和 Java 的 POJO（Plain Old Java Objects，普通老式 Java 对象）为数据库中的记录。

mybatis示例

1.porm.xml

<dependencies>
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.4.5</version>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.6</version>
    </dependency>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.12</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.16.20</version>
        <scope>provided</scope>
    </dependency>
</dependencies>

2.创建实体类和dao接口

3.创建SqlMapConfig

<!--    配置环境-->
        <environments default="mysql">
    <!--        配置MySQL环境-->
            <environment id="mysql">
    <!--            事务类型-->
                <transactionManager type="JDBC"></transactionManager>
    <!--            连接池-->
                <dataSource type="POOLED">
                    <!--            数据库连接基本信息-->
                    <property name="driver" value="com.mysql.jdbc.Driver"/>
                    <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
                    <property name="username" value="root"/>
                    <property name="password" value=""/>
                </dataSource>
            </environment>
        </environments>
    <!--    映射配置文件的位置 -->
        <mappers>
            <mapper resource="com/cc/mybatis/dao/UserDao.xml"></mapper>
        </mappers>
    </configuration>

4.创建映射配置文件UserDao.xml

 <mapper namespace="com.cc.mybatis.dao.UserDao">
    <select id="findAll" resultType="com.cc.mybatis.domain.User">
        select * from user
    </select>
</mapper>

5.操作数据库

 //1.读取配置文件
InputStream in = Resources.getResourceAsStream("SqlMapConfig");
//2.创建SqlSessionFactory
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(in);
//3.使用工厂生产SQLSession对象
SqlSession session = factory.openSession();
//创建dao接口的代理对象
UserDao userDao = session.getMapper(UserDao.class);
//代理对象执行方法
List<User> users = userDao.findAll();
for (User user : users) {
    System.out.println(user);
}
//释放资源
session.close();
in.close();
查询结果
/* User(id=56, username=cc, birthday=Wed May 22 00:00:00 CST 2019, sex=男, address=中国)
User(id=57, username=cc, birthday=Wed May 22 00:00:00 CST 2019, sex=男, address=中国)
User(id=58, username=cc, birthday=Wed May 22 00:00:00 CST 2019, sex=男, address=中国)
User(id=59, username=cc, birthday=Wed May 22 00:00:00 CST 2019, sex=男, address=中国)
User(id=60, username=cc, birthday=Wed May 22 00:00:00 CST 2019, sex=男, address=中国)*/

mybatis注解方式

删除UserDao.xml
在UserDao添加
@Select("select * from user") 
修改SqlMapperConfig
将
<mappers>
   <mapper resource="com/cc/mybatis/dao/UserDao.xml"></mapper>
</mappers>
替换为
<mappers>
    <mapper class="com.cc.mybatis.dao.UserDao"></mapper>
</mappers>

遇到的问题

Exception in thread "main" org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: org.apache.ibatis.executor.ExecutorException: A query was run and no Result Maps were found for the Mapped Statement 'com.cc.mybatis.dao.UserDao.findAll'.  It's likely that neither a Result Type nor a Result Map was specified.
### The error may exist in com/cc/mybatis/dao/UserDao.xml
### The error may involve com.cc.mybatis.dao.UserDao.findAll
### The error occurred while handling results
### SQL: select * from user
### Cause: org.apache.ibatis.executor.ExecutorException: A query was run and no Result Maps were found for the Mapped Statement 'com.cc.mybatis.dao.UserDao.findAll'.  It's likely that neither a Result Type nor a Result Map was specified.
	at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:150)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141)
	at org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:137)
	at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:75)
	at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:59)
	at com.sun.proxy.$Proxy2.findAll(Unknown Source)
	at com.cc.mybatis.test.MyBatisTest.main(MyBatisTest.java:33)
Caused by: org.apache.ibatis.executor.ExecutorException: A query was run and no Result Maps were found for the Mapped Statement 'com.cc.mybatis.dao.UserDao.findAll'.  It's likely that neither a Result Type nor a Result Map was specified.
	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.validateResultMapsCount(DefaultResultSetHandler.java:287)
	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSets(DefaultResultSetHandler.java:189)
	at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:64)
	at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79)
	at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:63)
	at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324)
	at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109)
	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148)
	... 6 more

Cause: org.apache.ibatis.executor.ExecutorException: A query was run and no Result Maps were found for the Mapped Statement ‘com.cc.mybatis.dao.UserDao.findAll’. It’s likely that neither a Result Type nor a Result Map was specified.

没有找到查询封装的对象的返回类型

UserDao.xml添加resultType=“com.cc.mybatis.domain.User”