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本文小編為大家詳細(xì)介紹“mybatis一對(duì)多嵌套查詢(xún)?cè)趺磳?shí)現(xiàn)”,內(nèi)容詳細(xì),步驟清晰,細(xì)節(jié)處理妥當(dāng),希望這篇“mybatis一對(duì)多嵌套查詢(xún)?cè)趺磳?shí)現(xiàn)”文章能幫助大家解決疑惑,下面跟著小編的思路慢慢深入,一起來(lái)學(xué)習(xí)新知識(shí)吧。
一個(gè)class中有許多student,屬于一對(duì)多關(guān)系。
本文利用mybatis注解,嵌套查詢(xún)方式來(lái)實(shí)現(xiàn)一對(duì)多查詢(xún),在根據(jù)classId查詢(xún)class時(shí),順便查詢(xún)并展示出class中的student
package com.itheima.dao; public class StudentDao { private Integer id; private String name; private Integer age; private Integer cid; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } public Integer getCid() { return cid; } public void setCid(Integer cid) { this.cid = cid; } @Override public String toString() { return "StudentDao{" + "id=" + id + ", name='" + name + '\'' + ", age=" + age + ", cid=" + cid + '}'; } }
package com.itheima.dao; import java.util.List; public class ClassDao { private Integer id; private String className; private List<StudentDao> studentsList; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getClassName() { return className; } public void setClassName(String className) { this.className = className; } @Override public String toString() { return "ClassDao{" + "id=" + id + ", className='" + className + '\'' + ", studentsList=" + studentsList + '}'; } }
<?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> <!--設(shè)置連接數(shù)據(jù)庫(kù)的環(huán)境--> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <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="root"/> </dataSource> </environment> </environments> <!--引入映射文件--> <mappers> <mapper class="com.itheima.mapper.StudentMapper"/> <mapper class="com.itheima.mapper.ClassMapper"/> </mappers> </configuration>
package com.itheima.mapper; import com.itheima.dao.StudentDao; import org.apache.ibatis.annotations.Many; import org.apache.ibatis.annotations.Result; import org.apache.ibatis.annotations.Results; import org.apache.ibatis.annotations.Select; import java.util.List; public interface StudentMapper { @Select("select * from student where cid = #{cid}") @Results({@Result(id = true, property = "id", column = "id"), @Result(property = "name",column = "name"), @Result(property = "age",column = "age"), @Result(property = "cid", column = "cid")}) List<StudentDao> selectStudentByCid(Integer cid); }
package com.itheima.mapper; import com.itheima.dao.ClassDao; import org.apache.ibatis.annotations.Many; import org.apache.ibatis.annotations.Result; import org.apache.ibatis.annotations.Results; import org.apache.ibatis.annotations.Select; import java.util.List; public interface ClassMapper { @Select("select * from class where id = #{id}") @Results({@Result(id =true, property = "id",column = "id"), @Result(property = "className",column = "className"), @Result(property ="studentsList",column = "id", many = @Many(select = "com.itheima.mapper.StudentMapper.selectStudentByCid"))}) ClassDao selectClassById(Integer id); }
testMybatis.java
import com.itheima.dao.ClassDao; import com.itheima.dao.StudentDao; import com.itheima.mapper.ClassMapper; import com.itheima.mapper.StudentMapper; import org.apache.ibatis.annotations.Mapper; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import org.junit.Test; import java.io.IOException; import java.io.InputStream; import java.util.List; public class testMybatis { @Test public void test() throws IOException { InputStream is = Resources.getResourceAsStream("mybatis-config.xml"); SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder(); SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is); SqlSession sqlSession = sqlSessionFactory.openSession(true); ClassMapper classMapper = sqlSession.getMapper(ClassMapper.class); ClassDao res = classMapper.selectClassById(2); System.out.println(res.toString()); } }
INSERT INTO `class` (`id`, `className`) VALUES (1, '軟件19-1'); INSERT INTO `class` (`id`, `className`) VALUES (2, '軟件19-2'); INSERT INTO `student` (`name`, `age`, `cid`, `id`) VALUES ('羅輯', 18, 2, 1); INSERT INTO `student` (`name`, `age`, `cid`, `id`) VALUES ('張三', 18, 2, 2); INSERT INTO `student` (`name`, `age`, `cid`, `id`) VALUES ('李四', 18, 2, 3);
查詢(xún)結(jié)果可看出,2班的班級(jí)信息和2班的學(xué)生信息
注意事項(xiàng):
1、一對(duì)多關(guān)系中,多方實(shí)體類(lèi)存一的那方的主鍵作為外鍵,‘’一‘’的那方的實(shí)體類(lèi)存‘’多‘’的那方的 list<多的那方的實(shí)體類(lèi)屬性>以便查詢(xún)時(shí)展示出來(lái)。
在“一”的那方的mapper接口中定義嵌套查詢(xún)。
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