Ibatis N:1避免N+1查询的方法

一、实体类

多方：public class Employ {private int id;private String enployName;private int salary;private Department department;public Employ() {}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getEnployName() {return enployName;}public void setEnployName(String enployName) {this.enployName = enployName;}public int getSalary() {return salary;}public void setSalary(int salary) {this.salary = salary;}public Department getDepartment() {return department;}public void setDepartment(Department department) {this.department = department;}}一方：public class Department {private int did;private String departmentName;private List<Employ> employees;public int getDid() {return did;}public void setDid(int did) {this.did = did;}public String getDepartmentName() {return departmentName;}public void setDepartmentName(String departmentName) {this.departmentName = departmentName;}public List<Employ> getEmployees() {return employees;}public void setEmployees(List<Employ> employees) {this.employees = employees;}}

 

二、映射文件

多方：<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE sqlMap         PUBLIC "-//ibatis.apache.org//DTD SQL Map 2.0//EN"         "http://ibatis.apache.org/dtd/sql-map-2.dtd"><sqlMap namespace="Employ">  <!-- Use type aliases to avoid typing the full classname every time. -->  <typeAlias alias="Employ" type="com.test.domain.Employ"/>  <!-- Result maps describe the mapping between the columns returned       from a query, and the class properties.  A result map isn't       necessary if the columns (or aliases) match to the properties       exactly. -->  <resultMap id="EmployResult" class="Employ">    <result property="id" column="id"/>    <result property="enployName" column="employ_name"/>    <result property="salary" column="salary"/>    <result property="department.did" column="did"/>    <result property="department.departmentName" column="department_name"/>  </resultMap>  <!-- Select with no parameters using the result map for Account class. -->  <select id="selectAllEmploy" resultMap="EmployResult">  <![CDATA[  select * from employees e, departments d where e.departmentid = d.did  ]]>  </select>  <!-- A simpler select example without the result map.  Note the       aliases to match the properties of the target result class. -->    <!-- Insert example, using the Account parameter class -->  <insert id="insertEmploy" parameterClass="Employ">  <![CDATA[  insert into employees (employ_name, salary, departmentid) values(#enployName#, #salary#, #department.did#)  ]]>  </insert>  <!-- Update example, using the Account parameter class -->  <!-- Delete example, using an integer as the parameter class --></sqlMap>一方：<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE sqlMap         PUBLIC "-//ibatis.apache.org//DTD SQL Map 2.0//EN"         "http://ibatis.apache.org/dtd/sql-map-2.dtd"><sqlMap namespace="Department">  <!-- Use type aliases to avoid typing the full classname every time. -->  <typeAlias alias="Department" type="com.test.domain.Department"/>  <!-- Result maps describe the mapping between the columns returned       from a query, and the class properties.  A result map isn't       necessary if the columns (or aliases) match to the properties       exactly. -->  <resultMap id="DepartmentResult" class="Department">    <result property="did" column="did"/>    <result property="departmentName" column="department_name"/>  </resultMap>  <!-- Select with no parameters using the result map for Account class. -->  <select id="selectDepartmentById" parameterClass="int" resultMap="DepartmentResult">  <![CDATA[  select * from departments where did = #did#  ]]>  </select>  <!-- A simpler select example without the result map.  Note the       aliases to match the properties of the target result class. -->    <!-- Insert example, using the Account parameter class -->  <insert id="insertDepartment" parameterClass="Department">  <![CDATA[  insert into departments (department_name) values(#departmentName#)  ]]>  </insert>  <!-- Update example, using the Account parameter class -->  <!-- Delete example, using an integer as the parameter class --></sqlMap>