Author: coolguy

mybatis的学习路线

• 1、基础，搭建开发环境
• 2、学习全局配置文件
• 3、学习sql映射文件
• 4、学习动态sql
• 5、缓存管理
• 6、mbg自动生成
• 7、运行原理
• 8、插件介绍
• 9、框架整合SSM
• 10、扩展

鉴别器：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。比如封装Employee：根据gender值
1、如果查出的是女生：就把部门信息查询出来，否则不查询；
2、如果是男生，把last_name这一列的值赋值给email;

1、搭建数据库

tbl_employee表【d_id 是外键 对应 tbl_dept表】

id	last_name    gender	  email       d_id
1	   mike	       0      [email protected]      1
2          book        0      [email protected]    2
3          tom         1      [email protected]    2
4          jerry       1       [email protected]       1

tbl_dept表：

id    dept_name
1      开发部
2      测试部

2、编辑 javabean

Employee.java

package com.mybatis.bean;

public class Employee {
	private int id;
	private String lastName;
	private String email;
	private String gender;
	private Department department;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getLastName() {
		return lastName;
	}

	public void setLastName(String lastName) {
		this.lastName = lastName;
	}

	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 Department getDepartment() {
		return department;
	}

	public void setDepartment(Department department) {
		this.department = department;
	}

	@Override
	public String toString() {
		return "Employee [id=" + id + ", lastName=" + lastName + ", email=" + email + ", gender=" + gender + "]";
	}

}

Department.java

package com.mybatis.bean;

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
				+ "]";
	}
	
	

}

3、编辑接口文件

EmployeeMapper.java

package com.mybatis.mapper;

import com.mybatis.bean.Employee;

public interface EmployeeMapper {
		
	public Employee getEmpByIdStep(Integer id);

}

DepartmentMapper.java

package com.mybatis.mapper;

import com.mybatis.bean.Department;

public interface DepartmentMapper {
	
	public Department getDeptById(Integer id);

}

4、编辑sql映射文件

EmployeeMapper.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.mybatis.mapper.EmployeeMapperPlus">

	<!--自定义某个javaBean的封装规则
	type：自定义规则的Java类型
	id:唯一id方便引用
	  -->
	  
	<!-- public Employee getEmpById(Integer id); -->
	<select id="getEmpByIdStep"  resultMap="MyEmpDis">
		select * from tbl_employee where id=#{id}
	</select>
	
	
	<!-- =======================鉴别器============================ -->
	<!-- <discriminator javaType=""></discriminator>
		鉴别器：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
		封装Employee：
			如果查出的是女生：就把部门信息查询出来，否则不查询；
			如果是男生，把last_name这一列的值赋值给email;
	 -->
	 <resultMap type="com.mybatis.bean.Employee" id="MyEmpDis">
	 	<id column="id" property="id"/>
	 	<result column="last_name" property="lastName"/>
	 	<result column="email" property="email"/>
	 	<result column="gender" property="gender"/>
	 	<!--
	 		column：指定判定的列名
	 		javaType：列值对应的java类型 ，string 是 mybatis 对String类型 直接默认设置 的别名 -->
	 	<discriminator javaType="string" column="gender">
	 		<!--女生  resultType:指定封装的结果类型；不能缺少。/resultMap-->
	 		<case value="0" resultType="com.mybatis.bean.Employee">
	 			<association property="department" 
			 		select="com.mybatis.mapper.DepartmentMapper.getDeptById"
			 		column="d_id">
		 		</association>
	 		</case>
	 		<!--男生 ;如果是男生，把last_name这一列的值赋值给email; -->
	 		<case value="1" resultType="com.mybatis.bean.Employee">
		 		<id column="id" property="id"/>
			 	<result column="last_name" property="lastName"/>
			 	<result column="last_name" property="email"/>
			 	<result column="gender" property="gender"/>
	 		</case>
	 	</discriminator>
	 </resultMap>
</mapper>

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.mybatis.mapper.DepartmentMapper">
	
	<!--public Department getDeptById(Integer id);  -->
	<select id="getDeptById" resultType="com.mybatis.bean.Department">
		select id,dept_name departmentName from tbl_dept where id=#{id}
	</select>

</mapper>

5、编辑全局配置文件：

mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
 PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

	<environments default="development">
		<environment id="development">
			<transactionManager type="JDBC" />
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.jdbc.Driver" />
				<property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
				<property name="username" value="root" />
				<property name="password" value="Kitty521!" />
			</dataSource>
		</environment>
	</environments>
	<!-- 将我们写好的sql映射文件（EmployeeMapper.xml）一定要注册到全局配置文件（mybatis-config.xml）中 
	如果 数据库全局文件 和 子配置文件 不在同一个目录 ，就需要 /目录/目录/.../EmployeeMapper_old.xml
	-->
	<mappers>
	    <!-- 新方法操作mybatis 需要 的配置文件 -->
		<mapper resource="EmployeeMapperPlus.xml"  />
		<mapper resource="DepartmentMapper.xml" />
	</mappers>
	
</configuration>

特别注意：分步查询需要 调用两句sql语句。因为这两句sql语句分布在两个不同的sql映射文件，所以两个sql映射文件都需要注册到 全局配置文件中。

1、搭建数据库

tbl_employee表【d_id 是外键 对应 tbl_dept表】

id	last_name    gender	  email       d_id
1	   mike	       0      [email protected]      1
2          book        0      [email protected]    2
3          tom         1      [email protected]    2
4          jerry       1       [email protected]       1

tbl_dept表：

id    dept_name
1      开发部
2      测试部

2、编辑 javabean

Employee.java

package com.mybatis.bean;

public class Employee {
	private int id;
	private String lastName;
	private String email;
	private String gender;
	private Department department;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getLastName() {
		return lastName;
	}

	public void setLastName(String lastName) {
		this.lastName = lastName;
	}

	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 Department getDepartment() {
		return department;
	}

	public void setDepartment(Department department) {
		this.department = department;
	}

	@Override
	public String toString() {
		return "Employee [id=" + id + ", lastName=" + lastName + ", email=" + email + ", gender=" + gender + "]";
	}

}

Department.java

package com.mybatis.bean;

import java.util.List;

public class Department {
	
	private Integer id;
	private String departmentName;
	private List<Employee> employees;
	
	
	public List<Employee> getEmployees() {
		return employees;
	}
	public void setEmployees(List<Employee> employees) {
		this.employees = employees;
	}
	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
				+ "]";
	}
	
	

}

3、编辑接口文件

DepartmentMapper.java

package com.mybatis.mapper;

import com.mybatis.bean.Department;

public interface DepartmentMapper {
	
	//分步查询
	public Department getDeptByIdStep(Integer id);

}

EmployeeMapper.java

package com.mybatis.mapper;

import java.util.List;

import com.mybatis.bean.Employee;

public interface EmployeeMapperPlus {
	
	public List<Employee> getEmpsByDeptId(Integer deptId);

}

4、编辑sql映射文件

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.mybatis.mapper.DepartmentMapper">
	
<!-- collection：分步查询 -->
	<resultMap type="com.mybatis.bean.Department" id="MyDeptStep">
		<id column="id" property="id"/>
		<id column="dept_name" property="departmentName"/>
		<collection property="employees" 
			select="com.mybatis.mapper.EmployeeMapperPlus.getEmpsByDeptId"
			column="id" fetchType="lazy"></collection>
	</resultMap>
	<!-- public Department getDeptByIdStep(Integer id); -->
	<select id="getDeptByIdStep" resultMap="MyDeptStep">
		select id,dept_name from tbl_dept where id=#{id}
	</select>

		<!-- 扩展：多列的值传递过去：
			将多列的值封装map传递；
			column="{key1=column1,key2=column2}"
		fetchType="lazy"：表示使用延迟加载；
				- lazy：延迟
				- eager：立即
	 -->
	
</mapper>

EmployeeMapper.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.mybatis.mapper.EmployeeMapperPlus">

	<!--自定义某个javaBean的封装规则
	type：自定义规则的Java类型
	id:唯一id方便引用
	  -->
	
	<!-- public List<Employee> getEmpsByDeptId(Integer deptId); -->
	<select id="getEmpsByDeptId" resultType="com.mybatis.bean.Employee">
		select * from tbl_employee where d_id=#{deptId}
	</select>

</mapper>

5、编辑全局配置文件：

mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
 PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

	<environments default="development">
		<environment id="development">
			<transactionManager type="JDBC" />
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.jdbc.Driver" />
				<property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
				<property name="username" value="root" />
				<property name="password" value="Kitty521!" />
			</dataSource>
		</environment>
	</environments>
	<!-- 将我们写好的sql映射文件（EmployeeMapper.xml）一定要注册到全局配置文件（mybatis-config.xml）中 
	如果 数据库全局文件 和 子配置文件 不在同一个目录 ，就需要 /目录/目录/.../EmployeeMapper_old.xml
	-->
	<mappers>
	    <!-- 新方法操作mybatis 需要 的配置文件 -->
		<mapper resource="EmployeeMapperPlus.xml"  />
		<mapper resource="DepartmentMapper.xml" />
	</mappers>
	
</configuration>

特别注意：分步查询需要 调用两句sql语句。因为这两句sql语句分布在两个不同的sql映射文件，所以两个sql映射文件都需要注册到 全局配置文件中。

6、补充说明

分步查询中：子句查询时（无论是association 还是 collection 标签），传入多个参数问题，延迟加载设置：

### 举例：
### fetchType="lazy" 代表子句执行时，用的是延迟加载。
### - lazy：延迟  
### - eager：立即

### 子查询 多个入参问题
### column="{deptId=id}" 代表 sql字段的 id ，传入给 子句查询中的 deptId 入参
### 将多列的值封装成map；column="{key1=column1,key2=column2}"  来传给子查询的入参

<collection property="employees" 
	select="com.mybatis.mapper.EmployeeMapperPlus.getEmpsByDeptId"
	column="{deptId=id}" fetchType="lazy">
</collection>

前面提到的关联查询中，bean里面的 某个属性就是一个对象，属于 一对一映射：可以采用一步查询，级联赋值 或者  采用分步查询 ，单独赋值。现在如果 bean的某个属性是 一个集合，属于一对多映射，那么 查询结果 就不能用级联赋值了。级联赋值 是 一对一 关系映射中的 一种方法。

1、搭建数据库

tbl_employee表【d_id 是外键 对应 tbl_dept表】

id	last_name    gender	  email       d_id
1	   mike	       0      [email protected]      1
2          book        0      [email protected]    2
3          tom         1      [email protected]    2
4          jerry       1       [email protected]       1

tbl_dept表：

id    dept_name
1      开发部
2      测试部

数据库测试：

select  d.id  did, d.dept_name dept_name, e.id eid, e.last_name last_name,
e.email email, e.gender gender
from tbl_dept d
left join tbl_employee e
on d.id = e.d_id
where d.id =1

2、编辑 javabean

Employee.java

package com.mybatis.bean;

public class Employee {
	private int id;
	private String lastName;
	private String email;
	private String gender;
	private Department department;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getLastName() {
		return lastName;
	}

	public void setLastName(String lastName) {
		this.lastName = lastName;
	}

	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 Department getDepartment() {
		return department;
	}

	public void setDepartment(Department department) {
		this.department = department;
	}

	@Override
	public String toString() {
		return "Employee [id=" + id + ", lastName=" + lastName + ", email=" + email + ", gender=" + gender + "]";
	}

}

Department.java

package com.mybatis.bean;

import java.util.List;

public class Department {
	
	private Integer id;
	private String departmentName;
        private List<Employee> employees;
        
        public List<Employee> getEmployees() {
		return employees;
	}
	public void setEmployees(List<Employee> employees) {
		this.employees = employees;
	}

	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
				+ "]";
	}
	
	

}

3、编辑接口文件

DepartmentMapper.java

package com.mybatis.mapper;

import com.mybatis.bean.Department;

public interface DepartmentMapper {
	
	//增强版 还能查出员工
	public Department getDeptByIdPlus(Integer id);

}

4、编辑sql映射文件

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.mybatis.mapper.DepartmentMapper">
	<!-- 
	public class Department {
			private Integer id;
			private String departmentName;
			private List<Employee> emps;
	  did  dept_name  ||  eid  last_name  email   gender  
	 -->
	 
	<!--嵌套结果集的方式，使用collection标签定义关联的集合类型的属性封装规则  -->
	<resultMap type="com.mybatis.bean.Department" id="MyDept">
		<id column="did" property="id"/>
		<result column="dept_name" property="departmentName"/>
		<!-- 
			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="employees" ofType="com.mybatis.bean.Employee">
			<!-- 定义这个集合中元素的封装规则 -->
			<id column="eid" property="id"/>
			<result column="last_name" property="lastName"/>
			<result column="email" property="email"/>
			<result column="gender" property="gender"/>
		</collection>
	</resultMap>
	<!-- public Department getDeptByIdPlus(Integer id); -->
	<select id="getDeptByIdPlus" resultMap="MyDept">
		SELECT d.id did,d.dept_name dept_name,
				e.id eid,e.last_name last_name,e.email email,e.gender gender
		FROM tbl_dept d
		LEFT JOIN tbl_employee e
		ON d.id=e.d_id
		WHERE d.id=#{id}
	</select>
</mapper>

5、编辑全局配置文件：

mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
 PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

	<environments default="development">
		<environment id="development">
			<transactionManager type="JDBC" />
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.jdbc.Driver" />
				<property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
				<property name="username" value="root" />
				<property name="password" value="Kitty521!" />
			</dataSource>
		</environment>
	</environments>
	<!-- 将我们写好的sql映射文件（EmployeeMapper.xml）一定要注册到全局配置文件（mybatis-config.xml）中 
	如果 数据库全局文件 和 子配置文件 不在同一个目录 ，就需要 /目录/目录/.../EmployeeMapper_old.xml
	-->
	<mappers>
		<mapper resource="DepartmentMapper.xml" />
	</mappers>
	
</configuration>

6、单元测试：

MybatisTest.java

package com.mybatis.test;


import java.io.IOException;
import java.io.InputStream;

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;

import com.mybatis.bean.Department;
import com.mybatis.bean.Employee;
import com.mybatis.mapper.DepartmentMapper;
import com.mybatis.mapper.EmployeeMapperPlus;


/**
 * 1、接口式编程
 * 	原生：		Dao		====>  DaoImpl
 * 	mybatis：	Mapper	====>  xxMapper.xml
 * 
 * 2、SqlSession代表和数据库的一次会话；用完必须关闭；
 * 3、SqlSession和connection一样她都是非线程安全。每次使用都应该去获取新的对象。(就是不要放在共享成员变量里面，A线程用完释放，B线程再用就为空了)
 * 4、mapper接口没有实现类，但是mybatis会为这个接口生成一个代理对象。
 * 		（将接口和xml进行绑定）
 * 		EmployeeMapper empMapper =	sqlSession.getMapper(EmployeeMapper.class);
 * 5、两个重要的配置文件：
 * 		mybatis的全局配置文件：包含数据库连接池信息，事务管理器信息等...系统运行环境信息
 * 		sql映射文件：保存了每一个sql语句的映射信息：
 * 					将sql抽取出来。	
 *
 */

public class MybatisTest {


	/********************************************************************/
	
	public SqlSessionFactory getSqlSessionFactory() throws IOException {
		String resource = "mybatis-config.xml";
		InputStream inputStream = Resources.getResourceAsStream(resource);
		return new SqlSessionFactoryBuilder().build(inputStream);
	}
	
	@Test
	public void test_new() throws IOException {
		// 1、获取sqlSessionFactory对象
		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
		// 2、获取sqlSession对象
		SqlSession openSession = sqlSessionFactory.openSession();
		try {
			// 3、获取接口的实现类对象
			//会为接口自动的创建一个代理对象，代理对象去执行增删改查方法

//			EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class);
//			Employee employee = mapper.getEmpByIdStep(1);
//			System.out.println(mapper.getClass());
//			System.out.println(employee);
//			System.out.println(employee.getDepartment());
			
			DepartmentMapper mapper = openSession.getMapper(DepartmentMapper.class);
			Department department = mapper.getDeptByIdPlus(1);
			System.out.println(mapper.getClass());
			System.out.println(department);
			System.out.println(department.getEmployees());

		} finally {
			openSession.close();
		}

	}

}