mybatis基于注解的多对一配置

相比于mybatis XML方法的配置方法，基于注解的方式更加简单一点。XML方式的配置需要在文件中配置许多东西。而基于注解的方式则只需要每次在具体实现类中在方法名上面加上注解即可。先看一个简单的例子：

一个用户多个账户查询

项目结构：

mybatis的主配置文件：

<?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">

<!--mybatis主配置文件-->
<configuration>
    <typeAliases>
        <package name="com.xatu.domain"></package>
    </typeAliases>
    <!--- 配置环境-->
    <environments default="mysql">
        <!---配置mysql的环境-->
        <environment id="mysql">
            <!--- 配置事务的类型-->
            <transactionManager type="JDBC"></transactionManager>
            <!--- 配置数据源(连接池)-->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///test1?characterEncoding=UTF-8&amp;useSSL=false&amp;serverTimezone=Asia/Shanghai"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
<!---指定映射配置文件的位置，映射配置文件指的是每个dao独立的配置文件 -->
    <mappers>
        <package name="com.xatu.dao"></package>
    </mappers>
</configuration>

User实体类

public class User implements Serializable {
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", birthday=" + birthday +
                ", sex='" + sex + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}

账户实体类

public class Account implements Serializable {
    private Integer id;
    private Integer uid;
    private double money;
    private User user;   //因为是通过账户Id查找用户  所以要有用户对象

    //多对一  (mybatis中称为一对一关系)
    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Integer getUid() {
        return uid;
    }

    public void setUid(Integer uid) {
        this.uid = uid;
    }

    public double getMoney() {
        return money;
    }

    public void setMoney(double money) {
        this.money = money;
    }

    @Override
    public String toString() {
        return "Account{" +
                "id=" + id +
                ", uid=" + uid +
                ", money=" + money +
                '}';
    }
}

操作类
IUserDao.java

public interface IUserDao {
    @Select("select * from user where id = #{id}")
    //通过用户id查找用户信息
    User findById(Integer userId);
}

IAccountDao.java

public interface IAccountDao {

    /**
     * 多表查询，查询所有
     * @return
     */
    @Select("select * from account")
    @Results(id="AccountMap",value ={
            @Result(id=true,column = "id",property = "id"),   //id=true 用来指定主键
            @Result(column = "uid",property = "uid"),
            @Result(column = "money",property = "money"),
            @Result(column = "uid",property = "user",one = @One(select = "com.xatu.dao.IUserDao.findById",fetchType=FetchType.EAGER))  //这样写的目的是在User表中通过uid查找。多对一就要使用@one标签
    })
    List<Account> findAll();
}

/**
除了@one标签  还有@many标签 对应多对多和一对多关系，除此之外FetchType也有三种属性
EAGER：预加载
DEFAULT：默认
LAZY：懒加载
*/

测试类
mybatisTest02 .java

public class mybatisTest02 {
    static private InputStream in=null;
    static private SqlSessionFactoryBuilder builder=null;
    static private SqlSessionFactory factory=null;
    static private SqlSession sqlSession=null;
    static private IAccountDao accountDao=null;
    @Before
    public void init() throws IOException {
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        builder=new SqlSessionFactoryBuilder();
        factory = builder.build(in);
        sqlSession = factory.openSession();
        accountDao = sqlSession.getMapper(IAccountDao.class);
    }
    @After
    public void destory() throws IOException {
        sqlSession.commit();
        sqlSession.close();
        in.close();
    }
    /**
     * 测试基于注解的mybatis使用
     */
    @Test
    public void TestfindAll()  {
        List<Account> accounts=accountDao.findAll();
        for (Account account:
                accounts) {
            System.out.println(account);
            System.out.println(account.getUser());
        }
    }
}