一、Select元素来定义查询操作

  • Id:唯一标识符。用来引用这条SQL语句,需要和接口的方法名一致
  • parameterType:参数类型。可以不传,MyBatis会根据TypeHandler自动推断
  • resultType:返回值类型。别名或者全类名,如果返回的是集合,定义集合中元素的类型。不能和resultMap同时使用

Employee对象

package com.nuch.edu.domain;

/**
* Created by yangshijing on 2017/12/4 0004.
*/
public class Employee {
private Integer id;
private String lastName;
private String email;
private String gender;
private Department dept; public Employee() {
} public Employee(String email, String gender, Integer id, String lastName) {
this.email = email;
this.gender = gender;
this.id = id;
this.lastName = lastName;
} public Department getDept() {
return dept;
} public void setDept(Department dept) {
this.dept = dept;
} public String getEmail() {
return email;
} public void setEmail(String email) {
this.email = email;
} public String getGender() {
return gender;
} public void setGender(String gender) {
this.gender = gender;
} public Integer getId() {
return id;
} public void setId(Integer id) {
this.id = id;
} public String getLastName() {
return lastName;
} public void setLastName(String lastName) {
this.lastName = lastName;
} @Override
public String toString() {
return "Employee{" +
"dept=" + dept +
", id=" + id +
", lastName='" + lastName + '\'' +
", email='" + email + '\'' +
", gender='" + gender + '\'' +
'}';
}
}

Department对象

package com.nuch.edu.domain;

import java.util.List;

public class Department {

    private Integer id;
private String departmentName; public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getDepartmentName() {
return departmentName;
}
public void setDepartmentName(String departmentName) {
this.departmentName = departmentName;
}
@Override
public String toString() {
return "Department [id=" + id + ", departmentName=" + departmentName
+ "]";
}
}

数据库中创建响应的表

DROP TABLE IF EXISTS `tbl_employee`;
CREATE TABLE `tbl_employee` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`last_name` varchar(255) DEFAULT NULL,
`gender` char(1) DEFAULT NULL,
`email` varchar(255) DEFAULT NULL,
`dept_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
DROP TABLE IF EXISTS `tbl_dept`;
CREATE TABLE `tbl_dept` (
`id` int(11) NOT NULL,
`dept_name` varchar(25) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

二、查询返回List结果集

resultType要指定集合中元素的类型

①.mapper接口

package com.nuch.edu.mapper;
import com.nuch.edu.domain.Employee;import java.util.List;/**
* Created by yangshijing on 2017/12/4 0004.
*/
public interface EmployeeMapper {public List<Employee> getEmpReturnList(String lastName); }

②.映射文件

<select id="getEmpReturnList" resultType="com.nuch.edu.domain.Employee">
SELECT * FROM tbl_employee
WHERE last_name like #{lastName}
</select>

③.测试代码

package com.nuch.edu;

import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.List;
import java.util.Map; import com.nuch.edu.domain.Employee;
import com.nuch.edu.mapper.EmployeeMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test; /**
* Created by yangshijing on 2017/12/4 0004.
*/
public class MybatisTest {
@Test
public void test1() throws IOException {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession sqlSession = sqlSessionFactory.openSession(); EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class); try {
//测试添加
//Employee employee = new Employee("tom@nchu.com", "0", null, "tom");
//mapper.addEmp(employee);
//System.out.print(employee.getId()); //测试删除
//mapper.deleteEmp(2); //测试更改
//Employee employee = new Employee("jerry@nchu.com","0",3,"jerry");
//mapper.updateEmp(employee); //测试参数
//Employee jerry = mapper.getEmpByIdAndLastName(3, "jerry"); //测试Map
  /*Map<String,Object> map = new HashMap<>();
map.put("id",3);
map.put("lastName","jerry");
Employee jerry = mapper.getEmpByMap(map);
System.out.print(jerry);*/ //测试返回map类型
 /* Map<String, Object> map = mapper.getEmpReturnMap("jerry");
System.out.print(map);*/ //测试返回List
List<Employee> list = mapper.getEmpReturnList("%t%");
System.out.print(list); //测试返回多条map记录
/*Map<String,Employee> map = mapper.getEmpReturnMap1("%t%");
System.out.print(map);*/ sqlSession.commit();
}finally {
sqlSession.close();
}
}
}

④.测试结果

DEBUG 12-19 13:47:37,089 ==>  Preparing: SELECT * FROM tbl_employee WHERE last_name like ?   (BaseJdbcLogger.java:145)
DEBUG 12-19 13:47:37,133 ==> Parameters: %t%(String) (BaseJdbcLogger.java:145)
DEBUG 12-19 13:47:37,174 <== Total: 2 (BaseJdbcLogger.java:145)
[Employee{dept=null, id=1, lastName='null', email='tom@qq.com', gender='1'}, Employee{dept=null, id=4, lastName='null', email='tom@nchu.com', gender='0'}]

三、返回Map结果集

返回一条记录的map;key就是列名,值就是对应的值;resultType指定为map

<select id="getEmpReturnMap" resultType="map">
SELECT * FROM tbl_employee
WHERE last_name = #{lastName}
</select>
 public Map<String,Object> getEmpReturnMap(String lastName);
Map<String, Object> map = mapper.getEmpReturnMap("jerry");
DEBUG 12-19 13:50:59,755 ==>  Preparing: SELECT * FROM tbl_employee WHERE last_name = ?   (BaseJdbcLogger.java:145)
DEBUG 12-19 13:50:59,809 ==> Parameters: jerry(String) (BaseJdbcLogger.java:145)
DEBUG 12-19 13:50:59,939 <== Total: 1 (BaseJdbcLogger.java:145)
{gender=0, last_name=jerry, id=3, dept_id=1, email=jerry@nchu.com}

多条记录封装为一个map,在mapper接口中的方法上加@MapKey注解;resultType指定为map中元素的类型

  • key:@Mapkey声明的属性
  • value:Employee对象
 /**
* 返回多条记录
* @param lastName
* @return
*/
@MapKey("lastName")
public Map<String,Employee> getEmpReturnMap1(String lastName);
 <select id="getEmpReturnMap1" resultType="com.nuch.edu.domain.Employee">
SELECT * FROM tbl_employee
WHERE last_name like #{lastName}
</select>
//测试返回多条map记录
Map<String,Employee> map = mapper.getEmpReturnMap1("%t%");
DEBUG 12-19 13:57:39,151 ==>  Preparing: SELECT * FROM tbl_employee WHERE last_name like ?   (BaseJdbcLogger.java:145)
DEBUG 12-19 13:57:39,215 ==> Parameters: %t%(String) (BaseJdbcLogger.java:145)
DEBUG 12-19 13:57:39,272 <== Total: 2 (BaseJdbcLogger.java:145)
{Tom=Employee{dept=null, id=1, lastName='Tom', email='tom@qq.com', gender='1'}, tom=Employee{dept=null, id=4, lastName='tom', email='tom@nchu.com', gender='0'}}

四、自动映射

1、全局setting设置

  • autoMappingBehavior默认是PARTIAL,开启自动映射的功能。唯一的要求是列名和javaBean属性名一致
  • 如果autoMappingBehavior设置为null则会取消自动映射数据库字段命名规范。POJO属性符合驼峰命名法,如A_COLUMN->aColumn,我们可以开启自动驼峰命名规则映射功能,mapUnderscoreToCamelCase=true。

2、自定义resultMap,实现高级结果集映射

  • id – 一个 ID 结果;标记结果作为 ID 可以帮助提高整体效能
  • result – 注入到字段或 JavaBean 属性的普通结果
<!--resultMap:自定义结果集映射规则
type:类的全限定名, 或者一个类型别名
id:当前命名空间中的一个唯一标识,用于标识一个result map.
-->
<resultMap id="myResultMap" type="com.nuch.edu.domain.Employee">
<!--id 和 result 都映射一个单独列的值到简单数据类型的单独属性或字段。
  column:从数据库中得到的列名,或者是列名的重命名标签。
  property:映射到列结果的字段或属性。
-->
<id column="id" property="id"></id>
<!-- 定义普通列封装规则 -->
<result column="last_name" property="lastName"></result>
<!-- 其他不指定的列会自动封装-->
</resultMap> <select id="getEmployeeByid" resultMap="myResultMap">
select id,last_name,email,gender from tbl_employee where id = #{id}
</select>

五、多表联合查询

当一个Javabean有对另一个对象的引用时,使用传统的resultType无法实现对引用的封装,这时要用到reslultMap

①.级联属性封装结果集

  /**
* 多表联合查询
*/
public Employee getEmpAndDep(Integer id);  
  <!--
   联合查询:级联属性封装结果集
  -->
  <resultMap id="test1" type="com.nuch.edu.domain.Employee">
<id column="id" property="id"></id>
<result column="last_name" property="lastName"></result>
<result column="gender" property="gender"></result>
<result column="email" property="email"></result>
<result column="did" property="dept.id"></result>
<result column="dept_name" property="dept.departmentName"></result>
</resultMap> <select id="getEmpAndDep" resultMap="test1">
SELECT d.id did ,d.dept_name dept_name ,
e.id id, e.last_name last_name,e.gender gender, e.email email
from tbl_dept d ,tbl_employee e
WHERE d.id = e.dept_id
and e.id = 1
</select>
  //测试多表查询
Employee empAndDep = mapper.getEmpAndDep(1);
System.out.print(empAndDep);
DEBUG 12-19 13:59:14,637 ==>  Preparing: SELECT d.id did ,d.dept_name dept_name , e.id id, e.last_name last_name,e.gender gender, e.email email from tbl_dept d ,tbl_employee e WHERE d.id = e.dept_id and e.id = 1   (BaseJdbcLogger.java:145)
DEBUG 12-19 13:59:14,682 ==> Parameters: (BaseJdbcLogger.java:145)
DEBUG 12-19 13:59:14,731 <== Total: 1 (BaseJdbcLogger.java:145)
Employee{dept=Department [id=1, departmentName=开发部], id=1, lastName='Tom', email='tom@qq.com', gender='1'}
②.association嵌套结果集
  <!--
使用association定义关联对象的封装规则;
-->
<resultMap id="test2" type="com.nuch.edu.domain.Employee">
<id column="id" property="id"></id>
<result column="last_name" property="lastName"></result>
<result column="gender" property="gender"></result>
<result column="email" property="email"></result>
<!-- association可以指定联合的javaBean对象
property="dept":指定哪个属性是联合的对象
javaType:指定这个属性对象的类型[不能省略]
-->
<association property="dept" javaType="com.nuch.edu.domain.Department">
      <!--column:数据库查询结果的列名
        property:联合对象的属性名
      -->
<id column="did" property="id"></id>
<result column="dept_name" property="departmentName"></result>
</association>
</resultMap> <select id="getEmpAndDep" resultMap="test2">
SELECT d.id did ,d.dept_name dept_name ,
e.id id, e.last_name last_name,e.gender gender, e.email email
from tbl_dept d ,tbl_employee e
WHERE d.id = e.dept_id
and e.id = 1
</select>

③.association分步查询

1.添加DepartmentMapper接口

package com.nuch.edu.mapper;

import com.nuch.edu.domain.Department;

/**
* Created by yangshijing on 2017/12/19 0019.
*/
public interface DepartmentMapper {
public Department getDepById(Integer id);
}

2.添加DepartmentMapper.xml映射文件

<?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.nuch.edu.mapper.DepartmentMapper">
<select id="getDepById" resultType="com.nuch.edu.domain.Department">
SELECT id ,dept_name departmentName FROM tbl_dept WHERE id = #{id}
</select>
</mapper>

3.类路径下的mybaits-config.xml引入映射文件

 <mappers>
<mapper resource="EmployeeMapper.xml"/>
<mapper resource="DepartmentMapper.xml"/>
</mappers>

4.EmployeeMapper接口添加方法

  public  Employee getEmpByStep(Integer id);

5.EmployeeMapper.xml添加映射

 <!-- 使用association进行分步查询:
1、先按照员工id查询员工信息
2、根据查询员工信息中的dept_id值去部门表查出部门信息
3、部门信息封装到员工属性中;
-->
<resultMap id="test3" type="com.nuch.edu.domain.Employee">
<id column="id" property="id"></id>
<result column="last_name" property="lastName"></result>
<result column="gender" property="gender"></result>
<result column="email" property="email"></result>
<!-- association定义关联对象的封装规则
select:调用目标的方法查询当前属性的值
column:将指定列的值传入目标方法 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,并封装给property指定的属性
-->
<association property="dept" select="com.nuch.edu.mapper.DepartmentMapper.getDepById"
column="dept_id">
</association>
</resultMap> <select id="getEmpByStep" resultMap="test3">
SELECT * FROM tbl_employee WHERE id=#{id}
</select>

6.测试代码

          //测试分步查询
/*Department depById = deptMapper.getDepById(1);
System.out.print(depById);*/
Employee empByStep = mapper.getEmpByStep(1);
System.out.print(empByStep);

7.结果

DEBUG 12-19 14:44:04,928 ==>  Preparing: SELECT * FROM tbl_employee WHERE id=?
DEBUG 12-19 14:44:05,102 ==> Parameters: 1(Integer)
DEBUG 12-19 14:44:05,130 ====> Preparing: SELECT id ,dept_name departmentName FROM tbl_dept WHERE id = ?
DEBUG 12-19 14:44:05,131 ====> Parameters: 1(Integer)
DEBUG 12-19 14:44:05,145 <==== Total: 1
DEBUG 12-19 14:44:05,146 <== Total: 1
Employee{dept=Department [id=1, departmentName=开发部], id=1, lastName='Tom', email='tom@qq.com', gender='1'}

六、assocation延时加载

1.开启延迟加载和属性按需加载;分步查询的基础之上加上两个配置:

<!-- 可以使用延迟加载(懒加载);(按需加载)
Employee==>Dept:
我们每次查询Employee对象的时候,都将一起查询出来。
部门信息在我们使用的时候再去查询;
-->
<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
<!-- 开启延时加载-->
<setting name="lazyLoadingEnabled" value="true"></setting>
<setting name="aggressiveLazyLoading" value="false"></setting>
</settings>

2.测试代码

Employee empByStep = mapper.getEmpByStep(1);
System.out.println(empByStep.getLastName());
System.out.println(empByStep.getDept());

3.结果

DEBUG 12-19 15:00:42,602 ==>  Preparing: SELECT * FROM tbl_employee WHERE id=?
DEBUG 12-19 15:00:42,666 ==> Parameters: 1(Integer)
DEBUG 12-19 15:00:42,824 <== Total: 1
Tom
DEBUG 12-19 15:00:42,825 ==> Preparing: SELECT id ,dept_name departmentName FROM tbl_dept WHERE id = ?
DEBUG 12-19 15:00:42,827 ==> Parameters: 1(Integer)
DEBUG 12-19 15:00:42,830 <== Total: 1
Department [id=1, departmentName=开发部]

七、Collection-集合类型&嵌套结果集

1.Department对象添加List<Employee>类型的属性

  private List<Employee> emps;

    public List<Employee> getEmps() {
return emps;
}
public void setEmps(List<Employee> emps) {
this.emps = emps;
}

2.DepartmentMapper接口添加方法

package com.nuch.edu.mapper;

import com.nuch.edu.domain.Department;

/**
* Created by yangshijing on 2017/12/19 0019.
*/
public interface DepartmentMapper {
public Department getDepCollection(Integer id);
}

3.DepartmentMapper.xml添加映射

<resultMap id="test1" type="com.nuch.edu.domain.Department">
<id column="did" property="id"></id>
<result column="dept_name" property="departmentName"></result>
<!--
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
-->
<collection property="emps" ofType="com.nuch.edu.domain.Employee">
<!-- 定义这个集合中元素的封装规则 -->
<id column="eid" property="id"></id>
<result column="gender" property="gender"></result>
<result column="last_name" property="lastName"></result>
<result column="email" property="email"></result>
</collection>
</resultMap>
<select id="getDepCollection" resultMap="test1">
SELECT d.id did,d.dept_name dept_name,
e.id eid,e.gender gender,e.last_name last_name ,e.email email
FROM tbl_dept d LEFT JOIN tbl_employee e
on d.id = e.dept_id
WHERE d.id = #{id};
</select>

4.测试代码

   //测试集合属性
Department depCollection = deptMapper.getDepCollection(1);
System.out.println(depCollection);
System.out.println(depCollection.getEmps());

5.结果

DEBUG 12-19 15:30:18,003 ==>  Preparing: SELECT d.id did,d.dept_name dept_name, e.id eid,e.gender gender,e.last_name last_name ,e.email email FROM tbl_dept d LEFT JOIN tbl_employee e on d.id = e.dept_id WHERE d.id = ?; 

DEBUG 12-19 15:30:18,090 ==> Parameters: 1(Integer)
DEBUG 12-19 15:30:18,127 <== Total: 2
Department [id=1, departmentName=开发部]
[Employee{id=1, lastName='Tom', email='tom@qq.com', gender='1'}, Employee{id=3, lastName='jerry', email='jerry@nchu.com', gender='0'}]

八、Collection-分步查询&延迟加载

1.DepartmentMapper接口添加方法

package com.nuch.edu.mapper;
import com.nuch.edu.domain.Department;
/**
* Created by yangshijing on 2017/12/19 0019.
*/
public interface DepartmentMapper {
public Department getDepByStep(Integer id);
}

2.DepartmentMapper.xml添加映射

  <resultMap id="test2" type="com.nuch.edu.domain.Department">
   <id column="id" property="id"></id>
   <result column="dept_name" property="departmentName"></result>
  <collection property="emps" ofType="com.nuch.edu.domain.Employee"
     select="com.nuch.edu.mapper.EmployeeMapper.getEmpByDepId" column="id">
   </collection>
</resultMap> <select id="getDepByStep" resultMap="test2">
SELECT * FROM tbl_dept WHERE id=#{id}
</select>

3.测试代码

Department depByStep = deptMapper.getDepByStep(1);
System.out.println(depByStep);
System.out.print(depByStep.getEmps());

4.结果

DEBUG 12-19 15:59:22,756 ==>  Preparing: SELECT * FROM tbl_dept WHERE id=?
DEBUG 12-19 15:59:22,819 ==> Parameters: 1(Integer)
DEBUG 12-19 15:59:23,020 <== Total: 1
DEBUG 12-19 15:59:23,022 ==> Preparing: SELECT * FROM tbl_employee WHERE dept_id = ?
DEBUG 12-19 15:59:23,023 ==> Parameters: 1(Integer)
DEBUG 12-19 15:59:23,028 <== Total: 2
Department [id=1, departmentName=开发部]
[Employee{id=1, lastName='Tom', email='tom@qq.com', gender='1'}, Employee{id=3, lastName='jerry', email='jerry@nchu.com', gender='0'}]

5.fetchType="lazy":表示使用延迟加载

- lazy:延迟
- eager:立即

association或者collection标签的 fetchType=eager/lazy可以覆盖全局的延迟加载策略, 指定立即加载(eager)或者延迟加载(lazy)

 <collection property="emps"   fetchType="lazy" select="com.nuch.edu.mapper.EmployeeMapper.getEmpByDepId" column="id">
</collection>

6.将多列的值封装map传递

<!--column="{key1=column1,key2=column2}-->
<!--key:select目标sql#{}中的名字-->
<collection property="emps" fetchType="lazy" select="com.nuch.edu.mapper.EmployeeMapper.getEmpByDepId" column="{dept_id=id}">

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