MyBatis进行级联查询

级联查询

1.创建实体类

        在pojo目录下创建需要的实体类

public class Account {private Integer aid;private Integer auserid;private Double amoney;private User user;//省略了无参、满参构造方法、get与set方法、toString方法
}

public class User {private Integer userid;private String username;private String useraddress;private String usersex;private String userbirthday;//一对多关系映射private List<Account> accounts;//省略了无参、满参构造方法、get与set方法、toString方法
}

2.一对一查询

1.AccountMapper接口

public interface AccountMapper {
//    一对一public Account getAccount(Integer aid);
}

2.AccountMapper.xml文件

一对一的分步查询

        在 <association> 元素中通常使用以下属性。

        ● property：指定映射到实体类的对象属性。

        ● column：指定表中对应的字段（即查询返回的列名）。

        ● javaType：指定映射到实体对象属性的类型。

        ● select：指定引入嵌套查询的子 SQL 语句，该属性用于关联映射中的嵌套查询

<!-- resultMap -->
<resultMap id="map1" type="com.ape.pojo.Account"><id property="aid" column="aid"></id><result property="auserid" column="auserid"></result><result property="amoney" column="amoney"></result><association property="user" javaType="com.ape.pojo.User" column="auserid"select="com.ape.dao.UserMapper.getUser"></association></resultMap>
<!-- 一对一 -->
<select id="getAccount" parameterType="int" resultMap="map1">select * from account where aid=#{aid};
</select>

3.UserMapper接口

public interface UserMapper {
//    一对一public User getUser(Integer userid);
}

4.UserMapper.xml文件

<!--   一对一--><select id="getUser" resultType="com.ape.pojo.User" parameterType="int">select * from user where userid=#{userid};</select>

5.创建测试类进行测试

public class AccountTest {InputStream is = null;SqlSessionFactoryBuilder ssfb = null;SqlSessionFactory factory = null;SqlSession session = null;@Beforepublic void before()throws  Exception{//1.主配置文件路径String path = "mybatis_config.xml";//2.转换为流对象is = Resources.getResourceAsStream(path);//3.创建工厂构造器对象ssfb = new SqlSessionFactoryBuilder();//4.创建工厂(构造者模式)factory =  ssfb.build(is);}@Afterpublic void after()throws  Exception{//资源回收session.close();is.close();}@Testpublic void test(){session=factory.openSession();AccountMapper dao=session.getMapper(AccountMapper.class);Account account=dao.getAccount(1);System.out.println(account);}
}

3.一对多查询

1.UserMapper接口

public interface UserMapper {
//    一对多public User getUserById(Integer userid);
}

2.UserMapper.xml文件

级联，分步

        在 <collection> 元素中通常使用以下属性。

        ● property：指定映射到实体类的对象属性。

        ● column：指定表中对应的字段（即查询返回的列名）。

        ● javaType：指定映射到实体对象属性的类型。

        ● select：指定引入嵌套查询的子 SQL 语句，该属性用于关联映射中的嵌套查询``

<!--   一对多--><select id="getUserById" resultMap="map2" parameterType="int">select * from user where userid=#{userid};</select><resultMap id="map2" type="com.ape.pojo.User"><id property="userid" column="userid"></id><result property="username" column="username"></result><result property="usersex" column="usersex"></result><result property="usersex" column="usersex"></result><result property="userbirthday" column="userbirthday"></result><collection property="accounts" ofType="com.ape.pojo.Account" column="userid"select="com.ape.dao.AccountMapper.getAccountByUserId"></collection></resultMap>

3.AccountMapper接口

public interface AccountMapper {
//    一对多public List<Account> getAccountByUserId(Integer userid);
}

4.AccountMapper.xml文件

<!--   一对多--><select id="getAccountByUserId" parameterType="int" resultType="com.ape.pojo.Account">select * from account where auserid=#{userid};</select>

5.创建测试类进行测试

public class UserTest {InputStream is = null;SqlSessionFactoryBuilder ssfb = null;SqlSessionFactory factory = null;SqlSession session = null;@Beforepublic void before()throws  Exception{//1.主配置文件路径String path = "mybatis_config.xml";//2.转换为流对象is = Resources.getResourceAsStream(path);//3.创建工厂构造器对象ssfb = new SqlSessionFactoryBuilder();//4.创建工厂(构造者模式)factory =  ssfb.build(is);}@Afterpublic void after()throws  Exception{//资源回收session.close();is.close();}@Testpublic void test1(){session=factory.openSession();UserMapper dao=session.getMapper(UserMapper.class);User user=dao.getUserById(46);System.out.println(user);}
}