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1,单个参数：mybatis不会做特殊处理

#{参数名/任意名}：取出参数值。

按照的思路

EmployeeMapper.java

public interface EmployeeMapper {   	public Employee getEmpByName(String name);}

EmployeeMapper.xml

   
   
        
            select * from employee where lastName=#{1};    >
   

MyBatisTest.java

@Test	public void test04() throws IOException{   				SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();		//1、获取到的SqlSession不会自动提交数据		SqlSession openSession = sqlSessionFactory.openSession();				try{   			EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);			//单个参数			Employee employee=mapper.getEmpByName("zlj");			System.out.println(employee);		}finally{   			openSession.close();		}	}

结果

结果我们知道在EmployeeMapper.xml中的查询语句中无论#[]中的值是否是EmployeeMapper.java中传入参数的值，仍然可以查询到结果，因为单个参数：mybatis不会做特殊处理

2，多个参数：mybatis会做特殊处理。

多个参数会被封装成 一个map，

EmployeeMapper.java

public interface EmployeeMapper {   	public Employee getEmpByIdAndLastName1(Integer id,String lastName);	public Employee getEmpByIdAndLastName2(@Param("id")Integer id,@Param("lastName")String lastName);	public Employee getEmpByIdAndLastName3(Integer id,String lastName);}

EmployeeMapper.xml

   
   	
     	
     		select * from employee where id = #{id} and last_name=#{lastName} 	 	
     	
     		select * from employee where id = #{id} and last_name=#{lastName} 	 	
     	
     		select * from employee where id = #{param1} and last_name=#{param2} 	>
   

MyBatisTest.java

@Test	public void test04() throws IOException{   				SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();		//1、获取到的SqlSession不会自动提交数据		SqlSession openSession = sqlSessionFactory.openSession();				try{   			EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);			//多个参数			Employee employee2=mapper.getEmpByIdAndLastName2(1, "zlj");			System.out.println(employee2);			Employee employee3=mapper.getEmpByIdAndLastName3(1, "zlj");			System.out.println(employee3);			Employee employee1=mapper.getEmpByIdAndLastName1(1, "zlj");			System.out.println(employee1);		}finally{   			openSession.close();		}	}

结果

结果可知道多个参数传进，多个参数会被封装成 一个map

key——》param1…paramN,或者参数的索引也可以

value——》：传入的参数值（#{param1}）

#{}就是从map中获取指定的key的值；

多个参数：mybatis会做特殊处理

异常：

3,命名参数 ：明确指定封装参数时map的key；@Param(“id”)

多个参数会被封装成 一个map，

4，POJO

如果多个参数正好是我们业务逻辑的数据模型，我们就可以直接传入pojo；

EmployeeMapper.java

public interface EmployeeMapper {   //以下测试POJO演示	public Employee getEmpByPOJO(Employee employee);

EmployeeMapper.xml

   
   
     	
     	
     		select * from employee where id=${id} and lastName=#{lastName} 	>
   

MyBatisTest.java

@Test	public void test04() throws IOException{   				SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();		//1、获取到的SqlSession不会自动提交数据		SqlSession openSession = sqlSessionFactory.openSession();				try{   			EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);			//POJO演示			Employee employee=new Employee(1,"zlj","22.@qq","add");			Employee employee2=mapper.getEmpByPOJO(employee);			System.out.println(employee2);		}finally{   			openSession.close();		}	}

结果

结果说明，如果多个参数正好是我们业务逻辑的数据模型，我们就可以直接传入pojo；

#{属性名}：取出传入的pojo的属性值

5，Map

如果多个参数不是业务模型中的数据，没有对应的pojo，不经常使用，为了方便，我们也可以传入map

EmployeeMapper.java

public interface EmployeeMapper {   //以下测试Map演示	public Employee getEmpByMap(Map
   
     map);}
   

EmployeeMapper.xml

   
   
     	
     	
     		select * from ${tableName} where id=${id} and last_name=#{lastName} 	>
   

MyBatisTest.java

@Test	public void test04() throws IOException{   				SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();		//1、获取到的SqlSession不会自动提交数据		SqlSession openSession = sqlSessionFactory.openSession();				try{   			EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);			//Map演示			Map
   
     map = new HashMap<>();			map.put("id", 2);			map.put("lastName", "Tom");			map.put("tableName", "employee");			Employee employee = mapper.getEmpByMap(map);						System.out.println(employee);		}finally{   			openSession.close();		}	}
   

结果

结果说明我们成功传入了map的值，#{key}：取出map中对应的值

6，参数值的获取

7，#{}:更丰富的用法