三(二)、對映檔案之select返回和resultMap
阿新 • • 發佈：2022-03-03
目錄結構同三(一)、mybatis對映檔案-增刪改和引數處理中的目錄結構
這裡需要再新增一張表：
CREATE TABLE `tbl_department` ( `id` int(11) NOT NULL AUTO_INCREMENT, `depart_name` varchar(255) DEFAULT NULL, PRIMARY KEY (`id`) ) ;
一、select 返回
1.select 返回物件：
如三(一)、mybatis對映檔案-增刪改和引數處理中的單個參數和多個引數中的查詢一樣；這裡不再多說了；
2.select 返回list
介面EmployeeMapper.java:
List<Employee> getEmps(String param);
對映檔案EmployeeMapper.xml;
- parameterType 可以不傳
- resultType 如果返回的是一個集合，要寫集合中元素的型別
<select id="getEmps" resultType="entity.Employee"> select ID AS id,LAST_NAME AS lastName,gender as gender,email as email from tbl_employee where LAST_NAME like #{e}</select>
junit 測試類：
1 @Test 2 public void test06() { 3 String resource = "mybatis-config.xml"; 4 SqlSession openSession = null; 5 try { 6 InputStream inputStream = Resources.getResourceAsStream(resource); 7 SqlSessionFactory sqlSessionFactory = newSqlSessionFactoryBuilder().build(inputStream); 8 // 獲取openSession 不會自動提交資料 9 openSession = sqlSessionFactory.openSession(true); 10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class); 11 12 List<Employee> employees = mapper.getEmps("%joy%"); 13 System.out.println("測試 select 返回list：" + employees); 14 15 } catch (Exception e) { 16 // TODO: handle exception 17 } finally { 18 if (openSession != null) { 19 openSession.close(); 20 } 21 22 } 23 }
執行結果：
測試 select 返回list：[Employee [id=1, lastName=joy33333, [email protected], gender=女], Employee [id=2, lastName=joy2x22222, [email protected], gender=男], Employee [id=4, lastName=joy, [email protected], gender=女], Employee [id=5, lastName=joy, [email protected], gender=女], Employee [id=6, lastName=joy, [email protected], gender=女], Employee [id=7, lastName=joy, [email protected], gender=女], Employee [id=8, lastName=joy, [email protected], gender=女], Employee [id=25, lastName=joy1111, [email protected], gender=女], Employee [id=26, lastName=joy222, [email protected], gender=女]]
3.select 返回單條資料的map
介面EmployeeMapper.java:
- 返回一條記錄的map，key就是列名，值就是對於的值
Employee getEmpByMap(Map<String, Object> map);
對映檔案EmployeeMapper.xml;
<select id="getMapById" resultType="map"> select ID AS id,LAST_NAME AS lastName,gender as gender,email as email from tbl_employee where id = #{id} </select>
junit 測試類：
1 @Test 2 public void test06() { 3 String resource = "mybatis-config.xml"; 4 SqlSession openSession = null; 5 try { 6 InputStream inputStream = Resources.getResourceAsStream(resource); 7 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 8 // 獲取openSession 不會自動提交資料 9 openSession = sqlSessionFactory.openSession(true); 10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class); 11 Map<String, Object> map = mapper.getMapById(1); 12 System.out.println("測試 select 返回單條資料的map：" + map); 13 14 } catch (Exception e) { 15 // TODO: handle exception 16 } finally { 17 if (openSession != null) { 18 openSession.close(); 19 } 20 21 } 22 }
執行結果：
測試 select 返回單條資料的map：{lastName=[B@202b0582, gender=女, id=1, [email protected]}
4.select 返回多條資料的map
介面EmployeeMapper.java:
- 多條記錄封裝一個map。Map<Integer, Employee> ：鍵是id,value 是資料物件
- @MapKey 告訴mybatis 封裝map的時候使用哪個屬性作為主鍵
@MapKey("id")
Map<Integer, Employee> getMaps();
對映檔案EmployeeMapper.xml：
<select id="getMaps" resultType="map"> select ID AS id,LAST_NAME AS lastName,gender as gender,email as email from tbl_employee </select>
junit 測試類：
1 @Test 2 public void test06() { 3 String resource = "mybatis-config.xml"; 4 SqlSession openSession = null; 5 try { 6 InputStream inputStream = Resources.getResourceAsStream(resource); 7 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 8 // 獲取openSession 不會自動提交資料 9 openSession = sqlSessionFactory.openSession(true); 10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class); 11 12 Map<Integer, Employee> maps = mapper.getMaps(); 13 System.out.println("測試 select 返回多條資料的map：" + maps); 14 15 } catch (Exception e) { 16 // TODO: handle exception 17 } finally { 18 if (openSession != null) { 19 openSession.close(); 20 } 21 22 } 23 }
執行結果：
測試 select 返回多條資料的map：{1={lastName=[B@268f106e, gender=女, id=1, [email protected]}, 2={lastName=[B@6e9a5ed8, gender=男, id=2, [email protected]}, 4={lastName=[B@7e057f43, gender=女, id=4, [email protected]}, 5={lastName=[B@6c284af, gender=女, id=5, [email protected]}, 6={lastName=[B@5890e879, gender=女, id=6, [email protected]}, 7={lastName=[B@6440112d, gender=女, id=7, [email protected]}, 8={lastName=[B@31ea9581, gender=女, id=8, [email protected]}, 9={lastName=[B@231f98ef, id=9, [email protected]}, 10={lastName=[B@7c137fd5, id=10, [email protected]}, 11={lastName=[B@183ec003, id=11, [email protected]}, 12={lastName=[B@7d9d0818, id=12, [email protected]}, 13={lastName=[B@221a3fa4, id=13, [email protected]}, 14={lastName=[B@451001e5, id=14, [email protected]}, 15={lastName=[B@2b40ff9c, gender=男, id=15, [email protected]}, 16={lastName=[B@3e08ff24, gender=男, id=16, [email protected]}, 17={lastName=[B@4d1c005e, gender=男, id=17, [email protected]}, 18={lastName=[B@8462f31, gender=男, id=18, [email protected]}, 19={lastName=[B@24569dba, gender=男, id=19, [email protected]}, 20={lastName=[B@5ddeb7cb, gender=男, id=20, [email protected]}, 21={lastName=[B@70ed52de, gender=男, id=21, [email protected]}, 22={lastName=[B@496bc455, gender=男, id=22, [email protected]}, 23={lastName=[B@59402b8f, gender=男, id=23, [email protected]}, 25={lastName=[B@7188af83, gender=女, id=25, [email protected]}, 26={lastName=[B@6be968ce, gender=女, id=26, [email protected]}}
二、resultMap：自定義某個javabean的封裝規則
實體類Employee.java新增的部門欄位：
1 package introduction; 2 3 public class Employee { 4 5 private Integer id; 6 private String lastName; 7 private String email; 8 private String gender; 9 private Department dept; 10 11 public Integer getId() { 12 return id; 13 } 14 15 public void setId(Integer id) { 16 this.id = id; 17 } 18 19 public String getLastName() { 20 return lastName; 21 } 22 23 public void setLastName(String lastName) { 24 this.lastName = lastName; 25 } 26 27 public String getEmail() { 28 return email; 29 } 30 31 public void setEmail(String email) { 32 this.email = email; 33 } 34 35 public String getGender() { 36 return gender; 37 } 38 39 public void setGender(String gender) { 40 this.gender = gender; 41 } 42 43 public Department getDept() { 44 return dept; 45 } 46 47 public void setDept(Department dept) { 48 this.dept = dept; 49 } 50 51 @Override 52 public String toString() { 53 return "Employee [id=" + id + ", lastName=" + lastName + ", email=" + email + ", gender=" + gender + ", dept=" 54 + dept + "]"; 55 } 56 57 }View Code
添加了部門的實體類：
1 package introduction; 2 3 import java.util.List; 4 5 public class Department { 6 7 private Integer id; 8 private String departmentName; 9 private List<Employee> empList; 10 11 public Integer getId() { 12 return id; 13 } 14 15 public void setId(Integer id) { 16 this.id = id; 17 } 18 19 public String getDepartmentName() { 20 return departmentName; 21 } 22 23 public void setDepartmentName(String departmentName) { 24 this.departmentName = departmentName; 25 } 26 27 public List<Employee> getEmpList() { 28 return empList; 29 } 30 31 public void setEmpList(List<Employee> empList) { 32 this.empList = empList; 33 } 34 35 @Override 36 public String toString() { 37 return "Department [id=" + id + ", departmentName=" + departmentName + "]"; 38 } 39 40 }View Code
1.自定義java bean 封裝規則的例項：
介面檔案EmployeeMapper.java：
Employee testResultType(Integer id);
對映檔案EmployeeMapper.xml:
1 <!-- 自定義某個javabean的封裝規則， type:自定義的java型別 id:唯一ID，方便引用 --> 2 <resultMap type="introduction.Employee" id="MyEmp"> 3 <!-- 指定主鍵列的封裝規則 id 定義主鍵，底層有優化 column：指定哪一列 property：指定對應的javabean屬性 --> 4 <id column="id" property="id" /> 5 <!-- 指定指定列封裝規則 不指定列會自動封裝 推薦 把全部的對映規則都寫上 --> 6 <result column="last_name" property="lastName" /> 7 <result column="email" property="email" /> 8 <result column="gender" property="gender" /> 9 </resultMap> 10 11 <select id="testResultType" resultMap="MyEmp"> 12 select 13 t01.* from 14 tbl_employee t01 where id=#{id} 15 </select>
Junit測試類：
1 @Test 2 public void test01() { 3 String resource = "mybatis-config.xml"; 4 SqlSession openSession = null; 5 try { 6 InputStream inputStream = Resources.getResourceAsStream(resource); 7 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 8 // 獲取openSession 不會自動提交資料 9 openSession = sqlSessionFactory.openSession(true); 10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class); 11 12 Employee testResultType = mapper.testResultType(1); 13 System.out.println("測試 stestResultType：" + testResultType); 14 } catch (Exception e) { 15 // TODO: handle exception 16 } finally { 17 if (openSession != null) { 18 openSession.close(); 19 } 20 21 } 22 }
執行結果：
測試 stestResultType：Employee [id=1, lastName=joy33333, [email protected], gender=女, dept=null]
2.關聯查詢級聯屬性封裝：
介面檔案EmployeeMapper.java：
1 package dao; 2 3 import introduction.Employee; 4 5 public interface EmployeeMapper { 6 7 Employee testResultType(Integer id); 8 9 }
對映檔案EmployeeMapper.xml
- type:自定義的java型別 id:唯一ID，方便引用
1 <?xml version="1.0" encoding="UTF-8" ?> 2 <!DOCTYPE mapper 3 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 4 "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> 5 <mapper namespace="dao.EmployeeMapper"> 6 7 8 <!-- 自定義某個javabean的封裝規則， type:自定義的java型別 id:唯一ID，方便引用 --> 9 <resultMap type="introduction.Employee" id="MyEmp"> 10 <!-- 指定主鍵列的封裝規則 id 定義主鍵，底層有優化 column：指定哪一列 property：指定對應的javabean屬性 --> 11 <id column="id" property="id" /> 12 <!-- 指定指定列封裝規則 不指定列會自動封裝 推薦 把全部的對映規則都寫上 --> 13 <result column="last_name" property="lastName" /> 14 <result column="email" property="email" /> 15 <result column="gender" property="gender" /> 16 <result column="d_id" property="dept.id" /> 17 <result column="depart_name" property="dept.departmentName" /> 18 </resultMap> 19 20 <select id="testResultType" resultMap="MyEmp"> 21 select 22 t01.*,t02.depart_name from 23 tbl_employee t01 left join tbl_department 24 t02 on t01.d_id = t02.id where t01.id =#{id} 25 </select> 26 </mapper>
junit測試類：
1 @Test 2 public void test01() { 3 String resource = "mybatis-config.xml"; 4 SqlSession openSession = null; 5 try { 6 InputStream inputStream = Resources.getResourceAsStream(resource); 7 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 8 // 獲取openSession 不會自動提交資料 9 openSession = sqlSessionFactory.openSession(true); 10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class); 11 12 Employee testResultType = mapper.testResultType(1); 13 System.out.println("測試 stestResultType：" + testResultType); 14 } catch (Exception e) { 15 // TODO: handle exception 16 } finally { 17 if (openSession != null) { 18 openSession.close(); 19 } 20 21 } 22 }
執行測試結果：
測試 stestResultType：Employee [id=1, lastName=joy33333, [email protected], gender=女, dept=Department [id=1, departmentName=開發部]]
3.關聯查詢association級聯屬性封裝：
介面檔案EmployeeMapper.java：
Employee testResultType2(Integer id);
對映檔案EmployeeMapper.xml
- type:自定義的java型別 id:唯一ID，方便引用
1 <!-- 自定義某個javabean的封裝規則， type:自定義的java型別 id:唯一ID，方便引用 --> 2 <resultMap type="introduction.Employee" id="MyEmp2"> 3 <!-- 指定主鍵列的封裝規則 id 定義主鍵，底層有優化 column：指定哪一列 property：指定對應的javabean屬性 --> 4 <id column="id" property="id" /> 5 <!-- 指定指定列封裝規則 不指定列會自動封裝 推薦 把全部的對映規則都寫上 --> 6 <result column="last_name" property="lastName" /> 7 <result column="email" property="email" /> 8 <result column="gender" property="gender" /> 9 <!-- association可以指定聯合的javaBean物件 10 property=”dept“ 指定哪個屬性是聯合的物件 11 javaType：指定這個屬性物件的型別；【不能省略】 12 --> 13 <association property="dept" 14 javaType="introduction.Department"> 15 <result column="d_id" property="id" /> 16 <result column="depart_name" property="departmentName" /> 17 </association> 18 </resultMap> 19 20 <select id="testResultType2" resultMap="MyEmp2"> 21 select 22 t01.*,t02.depart_name from 23 tbl_employee t01 left join tbl_department 24 t02 on t01.d_id = t02.id where t01.id =#{id} 25 </select>
junit測試類：
1 @Test 2 public void test02() { 3 String resource = "mybatis-config.xml"; 4 SqlSession openSession = null; 5 try { 6 InputStream inputStream = Resources.getResourceAsStream(resource); 7 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 8 // 獲取openSession 不會自動提交資料 9 openSession = sqlSessionFactory.openSession(true); 10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class); 11 12 Employee testResultType = mapper.testResultType2(1); 13 System.out.println("測試 stestResultType：" + testResultType); 14 } catch (Exception e) { 15 // TODO: handle exception 16 } finally { 17 if (openSession != null) { 18 openSession.close(); 19 } 20 21 } 22 }
執行結果：
測試 stestResultType：Employee [id=1, lastName=joy33333, [email protected], gender=女, dept=Department [id=1, departmentName=開發部]]
4.關聯查詢association 分步查尋：
介面檔案
EmployeeMapper.java：
Employee getEmpByIdStep(Integer id);
DepartmentMapper.java：
Department getDepartmentById(Integer id);
對映檔案EmployeeMapper.xml
- type:自定義的java型別 id:唯一ID，方便引用
1 <!-- 自定義某個javabean的封裝規則， type:自定義的java型別 id:唯一ID，方便引用 --> 2 <resultMap type="introduction.Employee" id="MyEmp3"> 3 <!-- 指定主鍵列的封裝規則 id 定義主鍵，底層有優化 column：指定哪一列 property：指定對應的javabean屬性 --> 4 <id column="id" property="id" /> 5 <!-- 指定指定列封裝規則 不指定列會自動封裝 推薦 把全部的對映規則都寫上 --> 6 <result column="last_name" property="lastName" /> 7 <result column="email" property="email" /> 8 <result column="gender" property="gender" /> 9 10 <!-- association 定義關聯物件的封裝規則 11 select: 表明當前屬性時呼叫select 指定的方法查出的結果 12 column：指定哪一列的值傳給方法 13 流程：使用select 指定的方法（傳入column指定的這列引數的值）查出物件，並封裝property物件 14 --> 15 <association property="dept" select="dao.DepartmentMapper.getDepartmentById" column="d_id"> 16 </association> 17 </resultMap> 18 19 <select id="getEmpByIdStep" resultMap="MyEmp3"> 20 SELECT * FROM tbl_employee WHERE ID= #{id} 21 </select>
DepartmentMapper.xml
1 <?xml version="1.0" encoding="UTF-8" ?> 2 <!DOCTYPE mapper 3 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 4 "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> 5 <mapper namespace="dao.DepartmentMapper"> 6 7 <select id="getDepartmentById" resultType="introduction.Department"> 8 SELECT id,depart_name as departmentName FROM TBL_DEPARTMENT WHERE ID= #{id} 9 </select> 10 11 </mapper>View Code
junit測試類：
1 @Test 2 public void test03() { 3 String resource = "mybatis-config.xml"; 4 SqlSession openSession = null; 5 try { 6 InputStream inputStream = Resources.getResourceAsStream(resource); 7 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 8 // 獲取openSession 不會自動提交資料 9 openSession = sqlSessionFactory.openSession(true); 10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class); 11 12 Employee testResultType = mapper.getEmpByIdStep(1); 13 System.out.println("測試 分步：" + testResultType); 14 } catch (Exception e) { 15 // TODO: handle exception 16 } finally { 17 if (openSession != null) { 18 openSession.close(); 19 } 20 21 } 22 }
執行結構：
測試 分步：Employee [id=1, lastName=joy33333, [email protected], gender=女, dept=Department [id=1, departmentName=開發部]]
5.分步查詢的懶載入說明
接著上面的執行結果，檢視控制檯查詢了兩條SQL：
此時，如果Junit測試只查詢單條一條SQL中的資料，那麼該分步查詢只執行一條SQL
1 @Test 2 public void test04() { 3 String resource = "mybatis-config.xml"; 4 SqlSession openSession = null; 5 try { 6 InputStream inputStream = Resources.getResourceAsStream(resource); 7 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 8 // 獲取openSession 不會自動提交資料 9 openSession = sqlSessionFactory.openSession(true); 10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class); 11 12 Employee testResultType = mapper.getEmpByIdStep(1); 13 System.out.println("測試 分步 只查一條SQL：" + testResultType.getLastName()); 14 } catch (Exception e) { 15 // TODO: handle exception 16 } finally { 17 if (openSession != null) { 18 openSession.close(); 19 } 20 21 } 22 }
執行結果為：
測試 分步 只查一條SQL：joy33333
檢視控制檯日誌：
6.關聯查詢 collection定義關聯封裝規則：
需求：查詢部門下所有的員工；所有員工放入 list中；即 部門物件中 把部門資訊放入對應的欄位，把該部門下的員工放入list中；
介面檔案EmployeeMapper.java：
Department getDepartmentByIdPlus(Integer id);
對映檔案EmployeeMapper.xml
- type:自定義的java型別 id:唯一ID，方便引用
1 <!-- collection 巢狀結果集的方式：定義關聯的集合型別元素的封裝規則 --> 2 3 <resultMap type="introduction.Department" id="MyDept"> 4 <id column="id" property="id" /> 5 <result column="depart_name" property="departmentName" /> 6 <!-- collection 定義關聯集合型別的屬性的封裝規則 ofType:指定集合裡面元素的型別 --> 7 <collection property="empList" 8 ofType="introduction.Employee"> 9 <id column="eid" property="id" /> 10 <result column="last_name" property="lastName" /> 11 <result column="gender" property="gender" /> 12 <result column="email" property="email" /> 13 </collection> 14 15 </resultMap> 16 <select id="getDepartmentByIdPlus" resultMap="MyDept"> 17 SELECT 18 T01.id, 19 T01.depart_name, 20 T02.id eid, 21 T02.last_name, 22 T02.gender, 23 T02.email 24 FROM 25 TBL_DEPARTMENT t01 26 LEFT JOIN tbl_employee T02 ON T01.ID = T02.D_ID 27 WHERE 28 T01.ID = #{id} 29 </select>
junit測試類：
1 @Test 2 public void test05() { 3 String resource = "mybatis-config.xml"; 4 SqlSession openSession = null; 5 try { 6 InputStream inputStream = Resources.getResourceAsStream(resource); 7 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 8 // 獲取openSession 不會自動提交資料 9 openSession = sqlSessionFactory.openSession(true); 10 DepartmentMapper mapper = openSession.getMapper(DepartmentMapper.class); 11 12 Department testResultType = mapper.getDepartmentByIdPlus(1); 13 System.out.println("測試 bean中的列表查詢：" + testResultType);// 顯示 一個部門資訊 14 System.out.println("測試 bean中的列表查詢：" + testResultType.getEmpList());// 部門下的所有員工 15 } catch (Exception e) { 16 // TODO: handle exception 17 } finally { 18 if (openSession != null) { 19 openSession.close(); 20 } 21 22 } 23 }
執行結果：
測試 bean中的列表查詢：Department [id=1, departmentName=開發部]
測試 bean中的列表查詢：[Employee [id=1, lastName=joy33333, [email protected], gender=女, dept=null], Employee [id=5, lastName=joy, [email protected], gender=女, dept=null]]
7.關聯查詢 collection 分步查詢：
同理可以實現懶載入，這裡不贅述了；
介面檔案EmployeeMapper.java：
Department getDepartmentByIdStep(Integer id);
對映檔案EmployeeMapper.xml
- type:自定義的java型別 id:唯一ID，方便引用
1 <!-- 分步查詢（可以實現懶載入） collection 巢狀結果集的方式：定義關聯的集合型別元素的封裝規則 --> 2 3 <resultMap type="introduction.Department" id="MyDept2"> 4 <id column="id" property="id" /> 5 <result column="depart_name" property="departmentName" /> 6 <!-- collection 定義關聯集合型別的屬性的封裝規則 ofType:指定集合裡面元素的型別 --> 7 <collection property="empList" 8 ofType="introduction.Employee" 9 select="dao.EmployeeMapper.getListByDid" column="{id=id}"> 10 </collection> 11 12 </resultMap> 13 <select id="getDepartmentByIdStep" resultMap="MyDept2"> 14 SELECT 15 T01.id, 16 T01.depart_name 17 18 FROM 19 TBL_DEPARTMENT t01 20 WHERE 21 T01.ID = #{id} 22 </select>
junit測試類：
1 @Test 2 public void test06() { 3 String resource = "mybatis-config.xml"; 4 SqlSession openSession = null; 5 try { 6 InputStream inputStream = Resources.getResourceAsStream(resource); 7 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 8 // 獲取openSession 不會自動提交資料 9 openSession = sqlSessionFactory.openSession(true); 10 DepartmentMapper mapper = openSession.getMapper(DepartmentMapper.class); 11 12 Department testResultType = mapper.getDepartmentByIdStep(1); 13 System.out.println("測試 bean中的列表查詢：" + testResultType.getDepartmentName());// 顯示 一個部門資訊 14 } catch (Exception e) { 15 // TODO: handle exception 16 } finally { 17 if (openSession != null) { 18 openSession.close(); 19 } 20 21 } 22 }
執行結果：
測試 bean中的列表查詢：開發部；
擴充套件內容：
多列值的傳遞； 將多列的值封裝map傳遞 column={key1=column1,key2=column}; key為 目標xml中的佔位符的名稱；即
SELECT * FROM tbl_employee WHERE D_ID= #{id}；id 其他屬性： fetchType="lazy":表示延遲載入；
按需載入 eager：表示立即 <collection property="empList" ofType="introduction.Employee"
select="dao.EmployeeMapper.getListByDid" column="{did=id}">
8.鑑別器：
說明：mybatis可以使用discriminator 判斷某列的值，然後根據某列的值改變封裝行為；
介面檔案EmployeeMapper.java：
Employee getEmpByIdStepDis(Integer id);
對映檔案EmployeeMapper.xml
- type:自定義的java型別 id:唯一ID，方便引用
1 <resultMap type="introduction.Employee" id="MyEmpDis"> 2 <id column="id" property="id" /> 3 <result column="last_name" property="lastName" /> 4 <result column="email" property="email" /> 5 <result column="gender" property="gender" /> 6 <discriminator javaType="string" column="gender"> 7 <case value="女" resultType="introduction.Employee"> 8 <association property="dept" select="dao.DepartmentMapper.getDepartmentById" column="d_id"> 9 </association> 10 </case> 11 <case value="男" resultType="introduction.Employee"> 12 <id column="id" property="id"/> 13 <result column="last_name" property="email" /> 14 <result column="email" property="lastName" /> 15 <result column="gender" property="gender" /> 16 </case> 17 </discriminator> 24 </resultMap> 25 26 <select id="getEmpByIdStepDis" resultMap="MyEmpDis"> 27 SELECT * FROM tbl_employee WHERE ID= #{id} 28 </select> 29 </mapper>
DepartmentMapper.xml:
1 <select id="getDepartmentById" 2 resultType="introduction.Department"> 3 SELECT id,depart_name as departmentName FROM TBL_DEPARTMENT WHERE ID= #{id} 4 </select>
junit測試類：
1 @Test 2 public void test07() { 3 String resource = "mybatis-config.xml"; 4 SqlSession openSession = null; 5 try { 6 InputStream inputStream = Resources.getResourceAsStream(resource); 7 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 8 // 獲取openSession 不會自動提交資料 9 openSession = sqlSessionFactory.openSession(true); 10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class); 11 12 Employee testResultType = mapper.getEmpByIdStepDis(2); 13 System.out.println("測試 bean中的列表查詢：" + testResultType); 14 } catch (Exception e) { 15 // TODO: handle exception 16 } finally { 17 if (openSession != null) { 18 openSession.close(); 19 } 20 21 } 22 }
執行結果：
測試 bean中的列表查詢：
測試 bean中的列表查詢：Employee [id=2, [email protected], email=joy2x22222, gender=男, dept=null]
如果把資料中該條記錄性別改為“女”：
測試 bean中的列表查詢：
測試 bean中的列表查詢：Employee [id=2, lastName=joy2x22222, [email protected], gender=女, dept=Department [id=2, departmentName=測試部]]
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