Mybatis3.1-[tp_32-33]-_對映檔案_select_resultMap關聯查詢_association分步查詢_延遲載入
阿新 • • 發佈：2018-12-01
筆記要點
出錯分析與總結
工程組織
1.定義介面
DepartmentMapper
package com.dao; import com.bean.Department; public interface DepartmentMapper { public Department getDeptById(Integer id); }View Code
EmployeeMapperPlus
package com.dao; import com.bean.*; public interfaceView CodeEmployeeMapperPlus { public Employee getEmpByIdStep(Integer id); //分步查詢 public Employee getEmpAndDept(Integer id);//關聯查詢 public Employee getEmpAndDept2(Integer id); //關聯查詢 ,使用association }
2.定義XML對映檔案
DepartmentMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dao.DepartmentMapper">
<!--public
View Code
EmployeeMapperPlus.xml
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.dao.EmployeeMapperPlus"> <!--ResultMap ;自定義結果集對映規則; type: 自定義規則的Java型別;id: 唯一的標識,方便引用--> <resultMap id="MySimpleEmp" type="com.bean.Employee"> <!--指定主鍵列的封裝規則,id定義主鍵,底層會有優化規則; column : 指定結果集的具體的那一列; property:指定的JavaBean對應的屬性--> <id column="id" property="id"/> <!--定義普通列的封裝規則--> <result column="last_name" property="lastName"/> <!--,其他不指定的列會自動封裝;但是, 我們只要寫ResultMap,就把剩下的對映全部都寫上--> <result column="email" property="email"/> <result column="gender" property="gender"/> </resultMap> <!--public Employee getEmpById(Integer id); 注意進行更改為resultMap--> <select id="getEmpById" resultMap="MySimpleEmp"> select * from tbl_employee where id=#{id} </select> <!--場景1,方法1:使用級聯屬性的方式 查詢Employee的同時查詢員工對應的部門Employee.dept=Department.id; 輸出員工對應的部門的全部資訊: id last_name gender did dept_name --> <resultMap id="MyDifEmp" type="com.bean.Employee"> <!--column : 指定結果集的具體的那一列; property:指定的JavaBean對應的屬性--> <id column="id" property="id"/> <result column="last_name" property="lastName"/> <result column="gender" property="gender"/> <result column="email" property="email"/> <result column="did" property="dept.id"/> <result column="dept_name" property="dept.departmentName"/> </resultMap> <!--public Employee getEmpAndDept2(Integer id); //association 定義封裝規則!--> <select id="getEmpAndDept" resultMap="MyDifEmp"> SELECT e.id id,e.last_name last_name,e.`gender` gender,e.`d_id` d_id, d.id did,d.`dept_name` dept_name,email FROM tbl_employee e,tbl_dept d WHERE e.`d_id`=d.`id` AND e.id=#{id}; </select> <!--方法2:-使用association可以指定聯合的javaBean的物件 --> <resultMap id="MyDifEmp2" type="com.bean.Employee"> <!--column : 指定結果集的具體的那一列; property:指定的JavaBean對應的屬性--> <id column="id" property="id"/> <result column="last_name" property="lastName"/> <result column="gender" property="gender"/> <result column="email" property="email"/> <!--使用association可以指定聯合的javaBean的物件;(定義單個物件的封裝規則!) property="dept";指定那個屬性是聯合的物件;javaType="dept";指定那個屬性物件的型別;--> <association property="dept" javaType="com.bean.Department"> <id column="did" property="id"/> <result column="dept_name" property="departmentName"/> </association> </resultMap> <!--public Employee getEmpAndDept2(Integer id); //關聯查詢--> <select id="getEmpAndDept2" resultMap="MyDifEmp2"> SELECT e.id id,e.last_name last_name,e.`gender` gender,e.`d_id` d_id, d.id did,d.`dept_name` dept_name,email FROM tbl_employee e,tbl_dept d WHERE e.`d_id`=d.`id` AND e.id=#{id}; </select> <!--使用association進行分步查詢, 1.先按照員工的id查詢員工資訊; 2.根據查詢員工資訊中的d_id值去部門表查出部門資訊; 3;,部門設定到員工中 --> <!--id last_name gender email d_id--> <resultMap id="MyEmpByStep" type="com.bean.Employee"> <id column="id" property="id" /> <result column="last_name" property="lastName"/> <!--association 定義關聯物件的封裝規則 select : 表明當前屬性是呼叫select總置頂的方法查出的結果! 總的流程: 使用select 指定的方法(傳入)查出物件,並封裝給property --> <association column="d_id" property="dept" select="com.dao.DepartmentMapper.getDeptById"> </association> </resultMap> <!--public Employee getEmpByIdStep(Integer id);--> <select id="getEmpByIdStep" resultMap="MyEmpByStep"> select * from tbl_employee where id=#{id} </select> <!--可以使用延遲載入,(按需載入,或者叫做懶載入) Employee==>dept: 我們可以每次查詢Employee物件的時候,都將一起查詢出來; 部門資訊在我們需要使用的時候再去查詢,分段查詢的基礎之上加兩個配置; --> <!-- 場景2: 查詢部門的時候將部門對應的所有員工的資訊也全部查詢出來 --> </mapper>View Code
3.編寫測試關聯查詢的 程式碼
public SqlSessionFactory getSqlSessionFactory() throws IOException { String resource = "mybatis-config.xml"; InputStream inputStream=Resources.getResourceAsStream(resource); return new SqlSessionFactoryBuilder().build(inputStream); } @Test public void test06() throws Exception { SqlSession openSession = getSqlSessionFactory().openSession(); try { EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class); System.out.println("---tp_30---多表關聯查詢,級聯屬性的封裝結果!--------"); Employee employee = mapper.getEmpAndDept(1); System.out.println(employee); System.out.println("---tp_31--多表關聯查詢,使用association進行連線!--------"); Employee employee2 = mapper.getEmpAndDept2(1); System.out.println(employee2); openSession.commit();//預設是不自動提交資料的,需要我們自己手動提交 } finally { openSession.close(); } }
測試結果
---tp_30---多表關聯查詢,級聯屬性的封裝結果!-------- DEBUG 12-01 15:13:43,362 ==> Preparing: SELECT e.id id,e.last_name last_name,e.`gender` gender,e.`d_id` d_id, d.id did,d.`dept_name` dept_name,email FROM tbl_employee e,tbl_dept d WHERE e.`d_id`=d.`id` AND e.id=?; (BaseJdbcLogger.java:145) DEBUG 12-01 15:13:43,380 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:145) DEBUG 12-01 15:13:43,391 <== Total: 1 (BaseJdbcLogger.java:145) Employee{id=1, lastName='jerry', email='[email protected]', gender='1', dept=Department{id=1, departmentName='開發部'}} ---tp_31--多表關聯查詢,使用association進行連線!-------- DEBUG 12-01 15:13:43,391 ==> Preparing: SELECT e.id id,e.last_name last_name,e.`gender` gender,e.`d_id` d_id, d.id did,d.`dept_name` dept_name,email FROM tbl_employee e,tbl_dept d WHERE e.`d_id`=d.`id` AND e.id=?; (BaseJdbcLogger.java:145) DEBUG 12-01 15:13:43,392 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:145) DEBUG 12-01 15:13:43,393 <== Total: 1 (BaseJdbcLogger.java:145) Employee{id=1, lastName='jerry', email='[email protected]', gender='1', dept=Department{id=1, departmentName='開發部'}} Process finished with exit code 0
在全域性配置檔案中 開啟延遲載入 (按需載入,或者叫做懶載入)
<settings> <setting name="mapUnderscoreToCamelCase" value="true"/> <setting name="jdbcTypeForNull" value="NULL"/> <!--顯示地指定每個我們需要更改的配置的值,及時他是預設的;防止版本替換帶來的問題--> <setting name="lazyLoadingEnabled" value="true"/> <setting name="aggressiveLazyLoading" value="false"/> </settings>
程式碼1 (仍使用上面的環境配置資訊, 此程式碼不呼叫到Department 資料庫 )
@Test public void test07() throws Exception{ SqlSession openSession = getSqlSessionFactory().openSession(); try { EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class); System.out.println("---tp_32---多表關聯查詢,使用association進行分佈查詢-----"); Employee employee = mapper.getEmpByIdStep(1); System.out.println(employee.getEmail()); // System.out.println(employee.getDept()); openSession.commit();//預設是不自動提交資料的,需要我們自己手動提交 }finally { openSession.close(); } }
結果1 (沒有進行Dept 上資料庫的關聯查詢)
---tp_32---多表關聯查詢,使用association進行分佈查詢----- DEBUG 12-01 15:18:57,230 ==> Preparing: select * from tbl_employee where id=? (BaseJdbcLogger.java:145) DEBUG 12-01 15:18:57,249 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:145) DEBUG 12-01 15:18:57,308 <== Total: 1 (BaseJdbcLogger.java:145) [email protected]163.com
程式碼2 (仍使用上面的環境配置資訊, 此程式碼可以呼叫到Department 資料庫 )
EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class); System.out.println("---tp_32---多表關聯查詢,使用association進行分佈查詢-----"); Employee employee = mapper.getEmpByIdStep(1); // System.out.println(employee.getEmail()); System.out.println(employee.getDept()); openSession.commit();//預設是不自動提交資料的,需要我們自己手動提交
結果2
---tp_32---多表關聯查詢,使用association進行分佈查詢----- DEBUG 12-01 15:19:50,044 ==> Preparing: select * from tbl_employee where id=? (BaseJdbcLogger.java:145) DEBUG 12-01 15:19:50,066 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:145) DEBUG 12-01 15:19:50,129 <== Total: 1 (BaseJdbcLogger.java:145) DEBUG 12-01 15:19:50,129 ==> Preparing: select id,dept_name departmentName from tbl_dept where id=? (BaseJdbcLogger.java:145) DEBUG 12-01 15:19:50,130 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:145) DEBUG 12-01 15:19:50,131 <== Total: 1 (BaseJdbcLogger.java:145) Department{id=1, departmentName='開發部'}