mybatis多表查询的实现(xml方式)

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

    //一对多映射关系，主表实体含有从表实体的集合引用
    private List<Account> accounts;

    public List<Account> getAccounts() {
        return accounts;
    }

    public void setAccounts(List<Account> accounts) {
        this.accounts = accounts;
    }

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

    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 String getAddress() {
        return address;
    }

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

    public String getSex() {
        return sex;
    }

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

    public Date getBirthday() {
        return birthday;
    }

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

public interface IUserDao {
    
    List<User> findAll();

    
    User findById(Integer uid);


}

public interface IAccountDao {
    
    List<Account> findAll();

    
    List<Account> findByUid(Integer uid);

}

<mapper namespace="com.cc.dao.IUserDao">
    <!--定义resultMap-->
    <!--因为在主配置文件中配置了domain包下的所有实体类别名，所以这里封装类型只需要写实体类名即可，不分大小写-->
    <resultMap id="userWithAccount" type="user">
        <!--封装user对象-->
        <id property="id" column="id"></id>
        <result property="username" column="username"></result>
        <result property="address" column="address"></result>
        <result property="sex" column="sex"></result>
        <result property="birthday" column="birthday"></result>
        <!--配置user队形中account集合的映射-->
        <!--定义一对多的关系映射，实现对account的封装，用collection标签
        ofType属性指定内容：要封装的实体对象类型
        select属性指定内容：查询用户的唯一标识
        column属性指定内容：用户根据id查询是所需要的参数
        -->
        <collection property="accounts" ofType="account" column="id" select="com.cc.dao.IAccountDao.findByUid"></collection>
    </resultMap>
    <!--查询所有-->
    <select id="findAll" resultMap="userWithAccount">
        select * from user
    </select>
    <!--根据id查询一个用户-->
    <select id="findById" parameterType="java.lang.Integer" resultType="user">
        select * from user where id=#{uid};
    </select>
</mapper>

<!--配置参数-->
    <settings>
        <!--开启Mybatis支持延时加载-->
        <setting name="lazyLoadingEnabled" value="true"/>
        <setting name="aggressiveLazyLoading" value="false"></setting>
    </settings>
    <!--配置domain包下所有实体类别名-->
    <typeAliases>
        <!--<typeAlias type="com.cc.domain.User" alias="user"></typeAlias>-->
        <package name="com.cc.domain"></package>
    </typeAliases>

public class UserTest {
    private InputStream in;
    private sqlSessionFactory factory;
    private SqlSession sqlSession;
    private IUserDao userDao;
    @Before//在测试方法执行之前执行
    public void init() throws IOException {
        //1.读取配置文件，生成字节输入流
         in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //2.生成SqlSessionFactory
         factory = new SqlSessionFactoryBuilder().build(in);
        //3.获取SqlSession
         sqlSession = factory.openSession();
        //4.获取dao的代理对象
         userDao = sqlSession.getMapper(IUserDao.class);
    }
    @After//在测试方法执行之后执行
    public void destory() throws IOException {
        //提交事务
        sqlSession.commit();
        //关闭资源
        sqlSession.close();
        in.close();
    }

    
    @Test
    public void TestFindAll() {
        //5.执行查询所有方法
        List<User> userList = userDao.findAll();
       for (User user : userList) {
           System.out.println(user);
            System.out.println(user.getAccounts());
        }

    }

}

public class Account implements Serializable {
    private Integer id;
    private Integer uid;
    private Double money;
    //从表实体应该包含一个主表实体的对象引用
    private User user;

    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 +
                '}';
    }
}

<mapper namespace="com.cc.dao.IAccountDao">
    <!--开启account支持二级缓存-->
    <cache/>
    <!--定义封装account和user的resultMap-->
    <resultMap id="accountAndUser" type="account">
        <id property="id" column="aid"></id>
        <result property="uid" column="uid"></result>
        <result property="money" column="money"></result>
        <!--定义一对一的关系映射，实现对user的封装
        select属性指定内容：查询用户的唯一标识
        column属性指定内容：用户根据id查询是所需要的参数
        fetchType属性指定内容：lazy延时加载，eager立即加载。
        -->
        <association property="user" column="uid" javaType="user" select="com.cc.dao.IUserDao.findById" fetchType="eager"></association>
    </resultMap>
    <!--查询所有-->
    <select id="findAll" resultMap="accountAndUser">
        SELECT * from account
    </select>
    <!--根据用户id查询-->
    <select id="findByUid" parameterType="java.lang.Integer" resultType="account" useCache="true">
        select * from account where uid = #{uid}
    </select>
</mapper>