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这篇文章将为大家详细讲解有关Mybatis中association和collection怎么用,小编觉得挺实用的,因此分享给大家做个参考,希望大家阅读完这篇文章后可以有所收获。
1.1实体之间的关联表示
package com.worldly.config.entity; import java.io.Serializable; /** * @Description * @Author xiaoqx <worldly_xuan@163.com> * @Version V1.0.0 * @Since 2017/11/26 */ public class Employee implements Serializable { private Integer id; private String name; private String email; private String tel; //关联的部门实体,查询某个人的时候可以把所在部门信息查询出来 private Department dep; 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 String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public String getTel() { return tel; } public void setTel(String tel) { this.tel = tel; } public Department getDep() { return dep; } public void setDep(Department dep) { this.dep = dep; } @Override public String toString() { return "{\"Employee\":{" + "\"id\":\"" + id + "\"" + ", \"name\":\"" + name + "\"" + ", \"email\":\"" + email + "\"" + ", \"tel\":\"" + tel + "\"" + ", \"dep\":" + dep + "}}"; } }
1.2 两种关联查询方式
//第一中方式:直接进行关联查询把关联实体的属性在xml中配置 //然后关联查出来 <resultMap id="emp2ResultMap" type="com.worldly.config.entity.Employee"> <id column="emp_id" property="id"></id> <result column="emp_name" property="name"/> <result column="emp_email" property="email"/> <result column="emp_tel" property="tel"/> <association property="dep" column="emp_dep" javaType="com.worldly.config.entity.Department"> <id column="dep_id" property="id"/> <result column="dep_name" property="name"/> <result column="dep_addr" property="addr"/> </association> </resultMap> <select id="selectEmployAll" resultMap="emp2ResultMap"> SELECT * FROM t_emp e INNER JOIN t_dep d ON e.emp_dep = d.dep_id </select>
//第二中查询方式,采用 association中的select来查询 <resultMap id="empResultMap" type="com.worldly.config.entity.Employee"> <id column="emp_id" property="id"></id> <result column="emp_name" property="name"/> <result column="emp_email" property="email"/> <result column="emp_tel" property="tel"/> <association column="emp_dep" property="dep" javaType="com.worldly.config.entity.Department" select="selectDepByCondition"></association> </resultMap> <select id="selectEmployeeList" resultMap="empResultMap" databaseId="mysql"> select * from t_emp </select> <resultMap id="depResultMap" type="com.worldly.config.entity.Department"> <id column="dep_id" property="id"></id> <result column="dep_name" property="name"/> <result column="dep_addr" property="addr"/> </resultMap> <select id="selectDepByCondition" resultMap="depResultMap"> SELECT * FROM t_dep d WHERE d.dep_id = #{emp_dep} </select>
1.3 两种方式的优劣
a.查询条件相同,所用的时间:从测试结果显示,关联查询要比嵌套查询快一点(结果不一定准确,可能关联表多的时候,结果会有所变化)
a.查询条件相同,所用的时间:从测试结果显示,关联查询要比嵌套查询快一点(结果不一定准确,可能关联表多的时候,结果会有所变化)
b.适用的情况
2.1实体之间的关联表示
package com.worldly.config.entity; import java.util.List; /** * @Description * @Author xiaoqx <worldly_xuan@163.com> * @Version V1.0.0 * @Since 1.0 * @Date 2017/12/16 */ public class Department { private int id; private String name; private String addr; List<Employee> employeeList; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getNamel() { return name; } public void setNamel(String name) { this.name = name; } public String getAddr() { return addr; } public void setAddr(String addr) { this.addr = addr; } public List<Employee> getEmployeeList() { return employeeList; } public void setEmployeeList(List<Employee> employeeList) { this.employeeList = employeeList; } @Override public String toString() { return "{\"Department\":{" + "\"id\":\"" + id + "\"" + ", \"name\":\"" + name + "\"" + ", \"addr\":\"" + addr + "\"" + ", \"employeeList\":" + employeeList + "}}"; } }
2.2 两种关联查询方式
//第一种方式嵌套查询 <resultMap id="depResultMap2" type="com.worldly.config.entity.Department"> <id column="dep_id" property="id"></id> <result column="dep_name" property="name"/> <result column="dep_addr" property="addr"/> <collection column="dep_id" property="employeeList" javaType="java.util.List" ofType="com.worldly.config.entity.Employee" select="selectEmpBydepId"/> </resultMap> <select id="selectDepByCondition" resultMap="depResultMap2"> SELECT * FROM t_dep d WHERE d.dep_id = #{param} </select> <resultMap id="empResultMap" type="com.worldly.config.entity.Employee"> <id column="emp_id" property="id"></id> <result column="emp_name" property="name"/> <result column="emp_email" property="email"/> <result column="emp_tel" property="tel"/> </resultMap> <select id="selectEmpBydepId" resultMap="empResultMap"> SELECT * FROM t_emp e WHERE e.emp_dep = #{dep_id} </select>
//第二中方式关联查询 <resultMap id="dep2ResultMap" type="com.worldly.config.entity.Department"> <id column="dep_id" property="id"></id> <result column="dep_name" property="name"/> <result column="dep_addr" property="addr"/> <collection property="employeeList" ofType="com.worldly.config.entity.Employee"> <id column="emp_id" property="id"></id> <result column="emp_name" property="name"/> <result column="emp_email" property="email"/> <result column="emp_tel" property="tel"/> </collection> </resultMap> <select id="selectDepWithEmp" resultMap="dep2ResultMap"> SELECT * FROM t_dep d INNER JOIN t_emp e ON d.dep_id = e.emp_dep WHERE d.dep_id = #{param} </select>
2.3 多条件查询
<resultMap id="depResultMap2" type="com.worldly.config.entity.Department"> <id column="dep_id" property="id"></id> <result column="dep_name" property="name"/> <result column="dep_addr" property="addr"/> <result column="dep_status" property="status"/> <collection column="{depId=dep_id,status=dep_status}" property="employeeList" javaType="java.util.List" ofType="com.worldly.config.entity.Employee" select="selectEmpBydepId"/> </resultMap> <select id="selectDepByCondition" resultMap="depResultMap2"> SELECT * FROM t_dep d WHERE d.dep_id = #{param} </select> <resultMap id="empResultMap" type="com.worldly.config.entity.Employee"> <id column="emp_id" property="id"></id> <result column="emp_name" property="name"/> <result column="emp_email" property="email"/> <result column="emp_tel" property="tel"/> </resultMap> <select id="selectEmpBydepId" resultMap="empResultMap"> SELECT * FROM t_emp e WHERE e.emp_dep = #{depId} AND e.emp_status=#{status} </select>
多条件查询,用{}来包装方法
3.1 鉴别器适用的场景
3.2 鉴别器的实现
这里只做最简单的用法,其它方法请自行查询;
<collection property="要查询的实体集合" javaType="java.util.List" ofType="要查询的实体所在包路径" select="要查询的mapper方法" column="关联的实体中的字段=关联的数据库中的字段"/>
举例
<collection property="stsManageStudentList" javaType="java.util.List" ofType="com.crm.project.domain.StsManageStudent" select="com.crm.project.mapper.StsManageStudentMapper.selectStsManageStudentList" column="manageId=manage_id"/>
<association property="要查询的实体" column="数据库中的关联字段" javaType="要查询的实体所在包路径" select="要查询的mapper方法"/>
举例
<association property="stsStudent" column="student_id" javaType="com.crm.project.domain.StsStudent" select="com.crm.project.mapper.StsStudentMapper.selectStsStudentById"/>
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