MyBatis笔记09 注解开发
coconutnut
 2020-04-02 21:45:52      

https://www.bilibili.com/video/BV1Db411s7F5

P68~75

环境搭建

导坐标

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<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>4.10</version>
  </dependency>
</dependencies>

准备实体类和接口

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public class User implements Serializable{

    private Integer id;
    private String username;
    private String address;
    private String sex;
    private Date birthday;
  
  	// get set ...

}
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public interface IUserDao {
  
  // ...
  
}

配置文件

映射配置文件可以不要了，但主配置文件不能省略

（如果使用注解开发，但相应路径下存在对应的xml，不管用不用都会报错）

SqlMapConfig.xml

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<?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>
    <!-- 引入外部配置文件-->
    <properties resource="jdbcConfig.properties"></properties>
    <!--配置别名-->
    <typeAliases>
        <package name="com.itheima.domain"></package>
    </typeAliases>
    <!-- 配置环境-->
    <environments default="mysql">
        <environment id="mysql">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"></property>
                <property name="url" value="${jdbc.url}"></property>
                <property name="username" value="${jdbc.username}"></property>
                <property name="password" value="${jdbc.password}"></property>
            </dataSource>
        </environment>
    </environments>
    <!-- 指定带有注解的dao接口所在位置 -->
    <mappers>
       <package name="com.itheima.dao"></package>
    </mappers>
</configuration>

jdbcConfig.properties中配置数据库连接信息

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jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/eesy_mybatis
jdbc.username=root
jdbc.password=1234

单表CRUD

在mybatis中针对CRUD共有四个注解：@Select @Insert @Update @Delete

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public interface IUserDao {

  	// 增
  	@Insert("insert into user(username,address,sex,birthday)values(#{username},#{address},#{sex},#{birthday})")
    void saveUser(User user);
  
  	// 删
  	@Delete("delete from user where id=#{id} ")
    void deleteUser(Integer userId);
  
  	// 改
  	@Update("update user set username=#{username},sex=#{sex},birthday=#{birthday},address=#{address} where id=#{id}")
    void updateUser(User user);
  
    // 查
    @Select("select * from user")
    List<User> findAll();
  
  	@Select("select * from user  where id=#{id} ")
    User findById(Integer userId);
  
  	// 方法一：这里#{username}没有%，查询时要传入如“%王%”
  	@Select("select * from user where username like #{username} ")
  	// 方法二：${}中固定写value，传参时不用写%
  	@Select("select * from user where username like '%${value}%' ")
    List<User> findUserByName(String username);
  	// 区别和之前一样，一个是字符串拼接，一个是参数占位符
  
  	@Select("select count(*) from user ")
    int findTotalUser();
  
}

测试

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public class AnnotationCRUDTest {
    private InputStream in;
    private SqlSessionFactory factory;
    private SqlSession session;
    private IUserDao userDao;

    @Before
    public  void init()throws Exception{
        // 1.获取字节输入流
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        // 2.根据字节输入流构建SqlSessionFactory
        factory = new SqlSessionFactoryBuilder().build(in);
        // 3.根据SqlSessionFactory生产一个SqlSession
        session = factory.openSession();
        // 4.使用SqlSession获取Dao的代理对象
        userDao = session.getMapper(IUserDao.class);
    }

    @After
    public  void destroy()throws  Exception{
        // 提交
        session.commit();
        // 释放资源
        session.close();
        in.close();
    }

    @Test
    public void testSave(){
        User user = new User();
        user.setUsername("mybatis annotation");
        user.setAddress("北京市昌平区");

        userDao.saveUser(user);
    }
  
  	// ...
}

实体类属性和数据库不对应问题

实体类中名称和表中对不上时（userName & username）

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public class User implements Serializable{

    private Integer userId;
    private String userName;
    private String userAddress;
    private String userSex;
    private Date userBirthday;

}

可以使用别名，但是所有位置都要使用别名，比较麻烦

可以使用@Results注解

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public interface IUserDao {

    @Select("select * from user")
    @Results(id="userMap",value={
            @Result(id=true,column = "id",property = "userId"),
            @Result(column = "username",property = "userName"),
            @Result(column = "address",property = "userAddress"),
            @Result(column = "sex",property = "userSex"),
            @Result(column = "birthday",property = "userBirthday")
    })
    List<User> findAll();
  
  	@Select("select * from user  where id=#{id} ")
    @ResultMap("userMap")
    User findById(Integer userId);
}

主键：id=true

其它位置用@ResultMap引用

标准写法@ResultMap(value={“userMap”})

由于只有一个属性，value可以省略；数组中只有一个元素，{}可以省略

于是可以直接写@ResultMap(“userMap”)

多表查询

实体类和接口

再建一个账户

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public class Account implements Serializable {

    private Integer id;
    private Integer uid;
    private Double money;
  
  	//多对一（mybatis中称为一对一）的映射：一个账户只能属于一个用户
    private User user;
  
  	// get set ...

}

修改用户实体类

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public class User implements Serializable{

    private Integer userId;
    private String userName;
    private String userAddress;
    private String userSex;
    private Date userBirthday;

    //一对多关系映射：一个用户对应多个账户
    private List<Account> accounts;
  
  	// get set ...
  
}

一对一查询

查账户以及所属的用户

IAccountDao中

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 	@Select("select * from account")
	@Results(id="accountMap",value = {
  @Result(id=true,column = "id",property = "id"),
  @Result(column = "uid",property = "uid"),
  @Result(column = "money",property = "money"),
  @Result(property = "user",column = "uid",one=@One(select="com.itheima.dao.IUserDao.findById",fetchType= FetchType.EAGER))
})
List<Account> findAll();

这里不使用left outer join，使用@One

select要找到能实现功能的方法，即IUserDao中findById，来查询账户所属的用户

FetchType可以配置延迟加载（LAZY），或立即加载（EAGER）

实际开发时对一一般选择立即加载，对多一般选择延迟加载

一对多查询

查一个用户，和该用户对应的多个账户

IUserDao中

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@Select("select * from user")
@Results(id="userMap",value={
  @Result(id=true,column = "id",property = "userId"),
  @Result(column = "username",property = "userName"),
  @Result(column = "address",property = "userAddress"),
  @Result(column = "sex",property = "userSex"),
  @Result(column = "birthday",property = "userBirthday"),
  @Result(property = "accounts",column = "id",
          many = @Many(select = "com.itheima.dao.IAccountDao.findAccountByUid",
                       fetchType = FetchType.LAZY))
})
List<User> findAll();

用@Many

IAccountDao中加一个方法

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@Select("select * from account where uid = #{userId}")
List<Account> findAccountByUid(Integer userId);

缓存配置

不管用xml还是注解，一级缓存默认都是开的

打开二级注解，全局配置默认也是打开

对于单个类，使用@CacheNamespace（默认是false）

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@CacheNamespace(blocking = true)
public interface IUserDao {
  // ...
}

即可开启二级缓存