數(shù)據(jù)表

CREATE TABLE `teacher`( id INT(10) NOT NULL, `name` VARCHAR(30) DEFAULT NULL, PRIMARY KEY (id)) ENGINE=INNODB DEFAULT CHARSET=utf8;INSERT INTO `teacher`(id,`name`) VALUES(1,’大師’);CREATE TABLE `student`( id INT(10) NOT NULL, `name` VARCHAR(30) DEFAULT NULL, `tid` INT(10) DEFAULT NULL, PRIMARY KEY(id), KEY `fktid` (`tid`), CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`)) ENGINE=INNODB DEFAULT CHARSET=utf8;INSERT INTO student(`id`,`name`,`tid`) VALUES(1,’小明’,1);INSERT INTO student(`id`,`name`,`tid`) VALUES(2,’小紅’,1);INSERT INTO student(`id`,`name`,`tid`) VALUES(3,’小張’,1);INSERT INTO student(`id`,`name`,`tid`) VALUES(4,’小李’,1);INSERT INTO student(`id`,`name`,`tid`) VALUES(5,’小王’,1);

Teacher 類

public class Teacher { private int id; private String name;}

Student 類

public class Student { private int id; private String name; private Teacher teacher;}

查詢接口

public interface StudentMapper { // 查詢嵌套處理 - 子查詢 List<Student> getStudentList(); // 結(jié)果嵌套處理 List<Student> getStudentResult();}查詢嵌套處理（子查詢）

思路：先查詢出所有學(xué)生的數(shù)據(jù)，再根據(jù)學(xué)生中關(guān)聯(lián)老師的字段 tid 用一個(gè)子查詢?nèi)ゲ樵兝蠋煹臄?shù)據(jù)

association：處理對(duì)象

property：實(shí)體類中屬性字段

column：查詢結(jié)果中需要傳遞給子查詢的字段

javaType：指定實(shí)體類

select：子查詢SQL

<mapper namespace='com.pro.dao.StudentMapper'> <!-- 按照查詢嵌套處理 1. 先查詢所有學(xué)生信息 2. 根據(jù)查詢出來學(xué)生的tid, 接一個(gè)子查詢?nèi)ゲ槔蠋? --> <resultMap type='com.pro.pojo.Student'> <result property='id' column='id'/> <result property='name' column='name'/> <!--復(fù)雜屬性需要單獨(dú)處理, 對(duì)象: association, 集合: collection --> <association property='teacher' column='tid' javaType='com.pro.pojo.Teacher' select='getTeacher'/> </resultMap> <select resultMap='StudentTeacher'> select * from student </select> <select resultType='com.pro.pojo.Teacher'> select * from teacher where id = #{id} </select></mapper>結(jié)果嵌套處理

思路：先把所有的信息一次性查詢處理， 然后配置字段對(duì)應(yīng)的實(shí)體類, 使用 association 配置

association：處理對(duì)象

property：實(shí)體類中屬性字段

javaType：指定實(shí)體類

<mapper namespace='com.pro.dao.StudentMapper'> <!-- 按照結(jié)果嵌套處理 1. 一次查詢出所有學(xué)生和老師的數(shù)據(jù) 2. 根據(jù)查詢的結(jié)果配置 association 對(duì)應(yīng)的屬性和字段 --> <resultMap type='com.pro.pojo.Student'> <result column='sid' property='id'/> <result column='sname' property='name'/> <!-- 根據(jù)查詢出來的結(jié)果, 去配置字段對(duì)應(yīng)的實(shí)體類 --> <association property='teacher' javaType='com.pro.pojo.Teacher'> <result column='tname' property='name'/> </association> </resultMap> <select resultMap='StudentResult'> SELECT s.id sid, s.name sname, t.name tname FROM student s, teacher t WHERE s.tid = t.id </select></mapper>

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