目录结构同三(一)、mybatis映射文件-增删改和参数处理 中的目录结构
这里需要再添加一张表：
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 返回对象：
如三(一)、mybatis映射文件-增删改和参数处理 中的单个参数和多个参数中的查询一样；这里不再多说了；
2.select 返回list
接口EmployeeMapper.java:
List<Employee> getEmps(String param);
映射文件EmployeeMapper.xml;
- parameterType 可以不传
- resultType 如果返回的是一个集合，要写集合中元素的类型
<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 测试类：
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 // 获取openSession 不会自动提交数据
9 openSession = sqlSessionFactory.openSession(true);
10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
11
12 List<Employee> employees = mapper.getEmps("%joy%");
13 System.out.println("测试 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 }
运行结果：
测试 select 返回list：[Employee [id=1, lastName=joy33333, email=joy52112225@iclound.com, gender=女], Employee [id=2, lastName=joy2x22222, email=joy52112225@iclound.com, gender=男], Employee [id=4, lastName=joy, email=joy521125@iclound.com, gender=女], Employee [id=5, lastName=joy, email=joy521125@iclound.com, gender=女], Employee [id=6, lastName=joy, email=joy521125@iclound.com, gender=女], Employee [id=7, lastName=joy, email=1602211057@qq.com, gender=女], Employee [id=8, lastName=joy, email=1602211058@qq.com, gender=女], Employee [id=25, lastName=joy1111, email=joy521125@icloud.com, gender=女], Employee [id=26, lastName=joy222, email=joy521125@icloud.com, gender=女]]
3.select 返回单条数据的map
接口EmployeeMapper.java:
- 返回一条记录的map，key就是列名，值就是对于的值
Employee getEmpByMap(Map<String, Object> map);
映射文件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 测试类：
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 // 获取openSession 不会自动提交数据
9 openSession = sqlSessionFactory.openSession(true);
10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
11 Map<String, Object> map = mapper.getMapById(1);
12 System.out.println("测试 select 返回单条数据的map：" + map);
13
14 } catch (Exception e) {
15 // TODO: handle exception
16 } finally {
17 if (openSession != null) {
18 openSession.close();
19 }
20
21 }
22 }
运行结果：
测试 select 返回单条数据的map：{lastName=[B@202b0582, gender=女, id=1, email=joy52112225@iclound.com}
4.select 返回多条数据的map
接口EmployeeMapper.java:
- 多条记录封装一个map。Map<Integer, Employee> ：键是id,value 是数据对象
- @MapKey 告诉mybatis 封装map的时候使用哪个属性作为主键
@MapKey("id")
Map<Integer, Employee> getMaps();
映射文件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 测试类：
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 // 获取openSession 不会自动提交数据
9 openSession = sqlSessionFactory.openSession(true);
10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
11
12 Map<Integer, Employee> maps = mapper.getMaps();
13 System.out.println("测试 select 返回多条数据的map：" + maps);
14
15 } catch (Exception e) {
16 // TODO: handle exception
17 } finally {
18 if (openSession != null) {
19 openSession.close();
20 }
21
22 }
23 }
运行结果：
测试 select 返回多条数据的map：{1={lastName=[B@268f106e, gender=女, id=1, email=joy52112225@iclound.com}, 2={lastName=[B@6e9a5ed8, gender=男, id=2, email=joy52112225@iclound.com}, 4={lastName=[B@7e057f43, gender=女, id=4, email=joy521125@iclound.com}, 5={lastName=[B@6c284af, gender=女, id=5, email=joy521125@iclound.com}, 6={lastName=[B@5890e879, gender=女, id=6, email=joy521125@iclound.com}, 7={lastName=[B@6440112d, gender=女, id=7, email=1602211057@qq.com}, 8={lastName=[B@31ea9581, gender=女, id=8, email=1602211058@qq.com}, 9={lastName=[B@231f98ef, id=9, email=zhumama@166.com}, 10={lastName=[B@7c137fd5, id=10, email=zhubaba@166.com}, 11={lastName=[B@183ec003, id=11, email=zhumama@166.com}, 12={lastName=[B@7d9d0818, id=12, email=zhubaba@166.com}, 13={lastName=[B@221a3fa4, id=13, email=zhumama@166.com}, 14={lastName=[B@451001e5, id=14, email=zhubaba@166.com}, 15={lastName=[B@2b40ff9c, gender=男, id=15, email=678@qq.com}, 16={lastName=[B@3e08ff24, gender=男, id=16, email=678@qq.com}, 17={lastName=[B@4d1c005e, gender=男, id=17, email=678@qq.com}, 18={lastName=[B@8462f31, gender=男, id=18, email=678@qq.com}, 19={lastName=[B@24569dba, gender=男, id=19, email=678@qq.com}, 20={lastName=[B@5ddeb7cb, gender=男, id=20, email=678@qq.com}, 21={lastName=[B@70ed52de, gender=男, id=21, email=678@qq.com}, 22={lastName=[B@496bc455, gender=男, id=22, email=678@qq.com}, 23={lastName=[B@59402b8f, gender=男, id=23, email=678@qq.com}, 25={lastName=[B@7188af83, gender=女, id=25, email=joy521125@icloud.com}, 26={lastName=[B@6be968ce, gender=女, id=26, email=joy521125@icloud.com}}
二、resultMap：自定义某个javabean的封装规则
实体类Employee.java添加的部门字段：
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
添加了部门的实体类：
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.自定义java bean 封装规则的实例：
接口文件EmployeeMapper.java：
Employee testResultType(Integer id);
映射文件EmployeeMapper.xml:
1 <!-- 自定义某个javabean的封装规则， type:自定义的java类型 id:唯一ID，方便引用 -->
2 <resultMap type="introduction.Employee" id="MyEmp">
3 <!-- 指定主键列的封装规则 id 定义主键，底层有优化 column：指定哪一列 property：指定对应的javabean属性 -->
4 <id column="id" property="id" />
5 <!-- 指定指定列封装规则 不指定列会自动封装 推荐 把全部的映射规则都写上 -->
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测试类：
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 // 获取openSession 不会自动提交数据
9 openSession = sqlSessionFactory.openSession(true);
10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
11
12 Employee testResultType = mapper.testResultType(1);
13 System.out.println("测试 stestResultType：" + testResultType);
14 } catch (Exception e) {
15 // TODO: handle exception
16 } finally {
17 if (openSession != null) {
18 openSession.close();
19 }
20
21 }
22 }
运行结果：
测试 stestResultType：Employee [id=1, lastName=joy33333, email=joy52112225@iclound.com, gender=女, dept=null]
2.关联查询级联属性封装：
接口文件EmployeeMapper.java：
1 package dao;
2
3 import introduction.Employee;
4
5 public interface EmployeeMapper {
6
7 Employee testResultType(Integer id);
8
9 }
映射文件EmployeeMapper.xml
- type:自定义的java类型 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 <!-- 自定义某个javabean的封装规则， type:自定义的java类型 id:唯一ID，方便引用 -->
9 <resultMap type="introduction.Employee" id="MyEmp">
10 <!-- 指定主键列的封装规则 id 定义主键，底层有优化 column：指定哪一列 property：指定对应的javabean属性 -->
11 <id column="id" property="id" />
12 <!-- 指定指定列封装规则 不指定列会自动封装 推荐 把全部的映射规则都写上 -->
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测试类：
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 // 获取openSession 不会自动提交数据
9 openSession = sqlSessionFactory.openSession(true);
10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
11
12 Employee testResultType = mapper.testResultType(1);
13 System.out.println("测试 stestResultType：" + testResultType);
14 } catch (Exception e) {
15 // TODO: handle exception
16 } finally {
17 if (openSession != null) {
18 openSession.close();
19 }
20
21 }
22 }
运行测试结果：
测试 stestResultType：Employee [id=1, lastName=joy33333, email=joy52112225@iclound.com, gender=女, dept=Department [id=1, departmentName=开发部]]
3.关联查询association级联属性封装：
接口文件EmployeeMapper.java：
Employee testResultType2(Integer id);
映射文件EmployeeMapper.xml
- type:自定义的java类型 id:唯一ID，方便引用
1 <!-- 自定义某个javabean的封装规则， type:自定义的java类型 id:唯一ID，方便引用 -->
2 <resultMap type="introduction.Employee" id="MyEmp2">
3 <!-- 指定主键列的封装规则 id 定义主键，底层有优化 column：指定哪一列 property：指定对应的javabean属性 -->
4 <id column="id" property="id" />
5 <!-- 指定指定列封装规则 不指定列会自动封装 推荐 把全部的映射规则都写上 -->
6 <result column="last_name" property="lastName" />
7 <result column="email" property="email" />
8 <result column="gender" property="gender" />
9 <!-- association可以指定联合的javaBean对象
10 property=”dept“ 指定哪个属性是联合的对象
11 javaType：指定这个属性对象的类型；【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测试类：
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 // 获取openSession 不会自动提交数据
9 openSession = sqlSessionFactory.openSession(true);
10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
11
12 Employee testResultType = mapper.testResultType2(1);
13 System.out.println("测试 stestResultType：" + testResultType);
14 } catch (Exception e) {
15 // TODO: handle exception
16 } finally {
17 if (openSession != null) {
18 openSession.close();
19 }
20
21 }
22 }
运行结果：
测试 stestResultType：Employee [id=1, lastName=joy33333, email=joy52112225@iclound.com, gender=女, dept=Department [id=1, departmentName=开发部]]
4.关联查询association 分步查寻：
接口文件
EmployeeMapper.java：
Employee getEmpByIdStep(Integer id);
DepartmentMapper.java：
Department getDepartmentById(Integer id);
映射文件EmployeeMapper.xml
- type:自定义的java类型 id:唯一ID，方便引用
1 <!-- 自定义某个javabean的封装规则， type:自定义的java类型 id:唯一ID，方便引用 -->
2 <resultMap type="introduction.Employee" id="MyEmp3">
3 <!-- 指定主键列的封装规则 id 定义主键，底层有优化 column：指定哪一列 property：指定对应的javabean属性 -->
4 <id column="id" property="id" />
5 <!-- 指定指定列封装规则 不指定列会自动封装 推荐 把全部的映射规则都写上 -->
6 <result column="last_name" property="lastName" />
7 <result column="email" property="email" />
8 <result column="gender" property="gender" />
9
10 <!-- association 定义关联对象的封装规则
11 select: 表明当前属性时调用select 指定的方法查出的结果
12 column：指定哪一列的值传给方法
13 流程：使用select 指定的方法（传入column指定的这列参数的值）查出对象，并封装property对象
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测试类：
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 // 获取openSession 不会自动提交数据
9 openSession = sqlSessionFactory.openSession(true);
10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
11
12 Employee testResultType = mapper.getEmpByIdStep(1);
13 System.out.println("测试 分步：" + testResultType);
14 } catch (Exception e) {
15 // TODO: handle exception
16 } finally {
17 if (openSession != null) {
18 openSession.close();
19 }
20
21 }
22 }
运行结构：
测试 分步：Employee [id=1, lastName=joy33333, email=joy52112225@iclound.com, gender=女, dept=Department [id=1, departmentName=开发部]]
5.分步查询的懒加载说明
接着上面的运行结果，查看控制台查询了两条SQL：
此时，如果Junit测试只查询单条一条SQL中的数据，那么该分步查询只执行一条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 // 获取openSession 不会自动提交数据
9 openSession = sqlSessionFactory.openSession(true);
10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
11
12 Employee testResultType = mapper.getEmpByIdStep(1);
13 System.out.println("测试 分步 只查一条SQL：" + testResultType.getLastName());
14 } catch (Exception e) {
15 // TODO: handle exception
16 } finally {
17 if (openSession != null) {
18 openSession.close();
19 }
20
21 }
22 }
运行结果为：
测试 分步 只查一条SQL：joy33333
查看控制台日志：
6.关联查询 collection定义关联封装规则：
需求：查询部门下所有的员工；所有员工放入 list中；即 部门对象中 把部门信息放入对应的字段，把该部门下的员工放入list中；
接口文件EmployeeMapper.java：
Department getDepartmentByIdPlus(Integer id);
映射文件EmployeeMapper.xml
- type:自定义的java类型 id:唯一ID，方便引用
1 <!-- collection 嵌套结果集的方式：定义关联的集合类型元素的封装规则 -->
2
3 <resultMap type="introduction.Department" id="MyDept">
4 <id column="id" property="id" />
5 <result column="depart_name" property="departmentName" />
6 <!-- collection 定义关联集合类型的属性的封装规则 ofType:指定集合里面元素的类型 -->
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测试类：
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 // 获取openSession 不会自动提交数据
9 openSession = sqlSessionFactory.openSession(true);
10 DepartmentMapper mapper = openSession.getMapper(DepartmentMapper.class);
11
12 Department testResultType = mapper.getDepartmentByIdPlus(1);
13 System.out.println("测试 bean中的列表查询：" + testResultType);// 显示 一个部门信息
14 System.out.println("测试 bean中的列表查询：" + testResultType.getEmpList());// 部门下的所有员工
15 } catch (Exception e) {
16 // TODO: handle exception
17 } finally {
18 if (openSession != null) {
19 openSession.close();
20 }
21
22 }
23 }
运行结果：
测试 bean中的列表查询：Department [id=1, departmentName=开发部]
测试 bean中的列表查询：[Employee [id=1, lastName=joy33333, email=joy52112225@iclound.com, gender=女, dept=null], Employee [id=5, lastName=joy, email=joy521125@iclound.com, gender=女, dept=null]]
7.关联查询 collection 分步查询：
同理可以实现懒加载，这里不赘述了；
接口文件EmployeeMapper.java：
Department getDepartmentByIdStep(Integer id);
映射文件EmployeeMapper.xml
- type:自定义的java类型 id:唯一ID，方便引用
1 <!-- 分步查询（可以实现懒加载） collection 嵌套结果集的方式：定义关联的集合类型元素的封装规则 -->
2
3 <resultMap type="introduction.Department" id="MyDept2">
4 <id column="id" property="id" />
5 <result column="depart_name" property="departmentName" />
6 <!-- collection 定义关联集合类型的属性的封装规则 ofType:指定集合里面元素的类型 -->
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测试类：
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 // 获取openSession 不会自动提交数据
9 openSession = sqlSessionFactory.openSession(true);
10 DepartmentMapper mapper = openSession.getMapper(DepartmentMapper.class);
11
12 Department testResultType = mapper.getDepartmentByIdStep(1);
13 System.out.println("测试 bean中的列表查询：" + testResultType.getDepartmentName());// 显示 一个部门信息
14 } catch (Exception e) {
15 // TODO: handle exception
16 } finally {
17 if (openSession != null) {
18 openSession.close();
19 }
20
21 }
22 }
运行结果：
测试 bean中的列表查询：开发部；
扩展内容：
多列值的传递； 将多列的值封装map传递 column={key1=column1,key2=column}; key为 目标xml中的占位符的名称；即
SELECT * FROM tbl_employee WHERE D_ID= #{id}；id 其他属性： fetchType="lazy":表示延迟加载；
按需加载 eager：表示立即 <collection property="empList" ofType="introduction.Employee"
select="dao.EmployeeMapper.getListByDid" column="{did=id}">
8.鉴别器：
说明：mybatis可以使用discriminator 判断某列的值，然后根据某列的值改变封装行为；
接口文件EmployeeMapper.java：
Employee getEmpByIdStepDis(Integer id);
映射文件EmployeeMapper.xml
- type:自定义的java类型 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测试类：
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 // 获取openSession 不会自动提交数据
9 openSession = sqlSessionFactory.openSession(true);
10 EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
11
12 Employee testResultType = mapper.getEmpByIdStepDis(2);
13 System.out.println("测试 bean中的列表查询：" + testResultType);
14 } catch (Exception e) {
15 // TODO: handle exception
16 } finally {
17 if (openSession != null) {
18 openSession.close();
19 }
20
21 }
22 }
运行结果：
测试 bean中的列表查询：
测试 bean中的列表查询：Employee [id=2, lastName=joy52112225@iclound.com, email=joy2x22222, gender=男, dept=null]
如果把数据中该条记录性别改为“女”：
测试 bean中的列表查询：
测试 bean中的列表查询：Employee [id=2, lastName=joy2x22222, email=joy52112225@iclound.com, gender=女, dept=Department [id=2, departmentName=测试部]]