03、MyBatis 映射文件

1.XML映射器

2.select

  Select元素来定义查询操作

   Id：唯一标识符

　　- 用来引用这条语句，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

1)返回List

public List getEmpsByLastNameLike(String lastName);

	
	
		select * from tbl_employee where last_name like #{lastName}
	

			List like = mapper.getEmpsByLastNameLike("%e%");
			
			for(Employee employee : like) {
				System.out.println(employee);
			}

2)返回单条Map数据

	//返回一条记录的map key:列名 value:值
	public Map getEmpByIdReturnMap(Integer id);

	
	
	
		select * from tbl_employee where id=#{id}
	

			Map map = mapper.getEmpByIdReturnMap(1);
			System.out.println(map);

3)返回多条Map数据

	//多条记录封装为一个map Map key:记录的主键  value:记录封装后的javabean
	//通知mybatis封装成这个map的时候使用那个属性作为主键
//	@MapKey("lastName")
//	public Map getEmpByLastNameLikeReturnMap(String lastName);
	@MapKey("id")
	public Map getEmpByLastNameLikeReturnMap(String lastName);

	
	
		select * from tbl_employee where last_name like #{lastName}
	

//			Map map = mapper.getEmpByLastNameLikeReturnMap("%r%");
//			System.out.println(map);
			Map map = mapper.getEmpByLastNameLikeReturnMap("%r%");
			System.out.println(map);

4)结果映射

　

5)高级结果映射

(1)自动映射

①.开启驼峰命名(默认规则)

  对比开启mapUnderscoreToCamelCase和不开启mapUnderscoreToCamelCase的区别.

  开启:Employee [id=1, lastName=plutoo, [email protected], gender=1]

  关闭:Employee [id=1, lastName=null, [email protected], gender=1]

  通过'开启'和'关闭'两个对比，我们清楚到在开启驼峰命名的情况下，mybatis会自动帮我们进行last_name的封装.

	
	
	
		select * from tbl_employee where id = #{id}
	

	@Test
	public void test05() throws IOException {
		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
		SqlSession openSession = sqlSessionFactory.openSession();
		
		try {
			EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class);
			Employee empById = mapper.getEmpById(1);
			System.out.println(empById);
		}finally {
			openSession.close();
		}
	}

②.关闭驼峰命名(自定义规则)

  对比开启mapUnderscoreToCamelCase和不开启mapUnderscoreToCamelCase的区别.

  开启:Employee [id=1, lastName=plutoo, [email protected], gender=1]

  关闭:Employee [id=1, lastName=plutoo, [email protected], gender=1]

  通过'开启'和'关闭'两个对比，我们是否开启驼峰命名的情况下，对mybatis我们进行last_name的封装并无影响,因为我们自定义了封装规则.

	public Employee getEmpById(Integer id);

	
		
	
	
	
	
	
		
		
		
		
		
		
		
		
		
		
		
	
	
	
	
	
	
	
		select * from tbl_employee where id = #{id}
	

	@Test
	public void test05() throws IOException {
		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
		SqlSession openSession = sqlSessionFactory.openSession();
		
		try {
			EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class);
			Employee empById = mapper.getEmpById(1);
			System.out.println(empById);
		}finally {
			openSession.close();
		}
		
	}

(2)resultMap的应用场景

①.查询Employee的同时查询员工对应的部门(联合查询) Employee===Department

(1.数据表的创建

CREATE TABLE tbl_dept(
  id INT(11) PRIMARY KEY AUTO_INCREMENT,
  dept_name VARCHAR(255)
)

(2.添加外键约束

ALTER TABLE tbl_employee ADD COLUMN d_id INT(11);
ALTER TABLE tbl_employee ADD CONSTRAINT fk_emp_dept
FOREIGN KEY(d_id) REFERENCES tbl_dept(id); 

(3.配置resultMap

	public Employee getEmpAndDept(Integer id);

	
	
		
		
		
		
		
	
	
	
	
	
	
		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 
		FROM tbl_employee e,tbl_dept d
		WHERE e.d_id=d.id AND e.id=#{id}
	

	@Test
	public void test05() throws IOException {
		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
		SqlSession openSession = sqlSessionFactory.openSession();	
		try {
			EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class);
			Employee empAndDept = mapper.getEmpAndDept(1);
			System.out.println(empAndDept);
			System.out.println(empAndDept.getDept());
		}finally {
			openSession.close();
		}
	}

②.查询Employee的同时查询员工对应的部门(association) Employee===Department　

	public Employee getEmpAndDept(Integer id);

	
	
		
		
		
		
		
		
		
		
		
			
			
		
	
	
	
	
	
	
		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 
		FROM tbl_employee e,tbl_dept d
		WHERE e.d_id=d.id AND e.id=#{id}
	

	@Test
	public void test05() throws IOException {
		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
		SqlSession openSession = sqlSessionFactory.openSession();	
		try {
			EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class);
			Employee empAndDept = mapper.getEmpAndDept(1);
			System.out.println(empAndDept);
			System.out.println(empAndDept.getDept());
		}finally {
			openSession.close();
		}
	}

③.查询Employee的同时查询员工对应的部门(association分步查询)

(1.Department.java

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 + "]";
	}
	
} 

(2.DepartmentMapper.java　

public interface DepartmentMapper {

	public Department getDeptById(Integer id);
}

(3.EmployeeMapperPlus.java

public interface EmployeeMapperPlus {
	public Employee getEmpByIdStep(Integer id);
}

(4.DepartmentMapper.xml

	
	
		select dept_name departmentName,id from tbl_dept where id=#{id}
	

(5.Employee.java

public class Employee {

	private Integer id;
	private String lastName;
	private String email;
	private String gender;
	private Department dept;
	
	public Department getDept() {
		return dept;
	}
	public void setDept(Department dept) {
		this.dept = dept;
	}
	public Employee() {
		super();
		// TODO Auto-generated constructor stub
	}
	public Employee(Integer id, String lastName, String email, String gender) {
		this.id = id;
		this.lastName = lastName;
		this.email = email;
		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;
	}
	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;
	}
	@Override
	public String toString() {
		return "Employee [id=" + id + ", lastName=" + lastName + ", email=" + email + ", gender=" + gender + "]";
	}
}

(6.EmployeeMapperPlus.xml

	
	
		
	 	
	 	
	 	
	 	
	 	
	 	
	 	
	 	
	 	
	 	
	
	
	
	
	
	
	
	
		select * from tbl_employee where id=#{id}
	

(7.MyBatisTest.java

	@Test
	public void test05() throws IOException {
		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
		SqlSession openSession = sqlSessionFactory.openSession();
		
		try {
			EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class);
			Employee employee = mapper.getEmpByIdStep(1);
			System.out.println(employee);
			System.out.println(employee.getDept());
		}finally {
			openSession.close();
		}
	}

(8.延迟加载

  观察Test中的查询两条的结果.通过控制台我们可以知道，开启了延迟加载后.我们查询的结果为单条单条的查询,按查询需要给控制台，不会一下子把查询结果全部给控制台.

  旧版本的MyBatis需要额外的支持包

– asm-3.3.1.jar

– cglib-2.2.2.jar

			System.out.println(employee);
-------------------------------------------------------------------------------------------
			System.out.println(employee);
			System.out.println(employee.getLastName());

④.查询部门的时候将部门对应的所有员工信息也查询出来

public class Department {

	private Integer id;
	private String departmentName;
	private List emps;
}

	
	
	
	
		
		
		
		
			
		
			
			
			
			
			
		
	
	
	
	
		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}
	

	@Test
	public void test06() throws IOException {
		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
		SqlSession openSession = sqlSessionFactory.openSession();
		
		try {
			DepartmentMapper mapper = openSession.getMapper(DepartmentMapper.class);
			Department department = mapper.getDeptByIdPlus(1);
			System.out.println(department);
			System.out.println(department.getEmps());
		}finally {
			openSession.close();
		}
	}

⑤.查询部门的时候将部门对应的所有员工信息也查询出来(分步查询)

public interface EmployeeMapperPlus {
	public List getEmpsByDeptId(Integer deptId);
}

　　

	
	
	
		select * from tbl_employee where d_id=#{deptId}
	

　　

	
	
		
		
		
		
		
	
	
	
	
		select id,dept_name departmentName from tbl_dept where id=#{id}
	

　　

	@Test
	public void test06() throws IOException {
		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
		SqlSession openSession = sqlSessionFactory.openSession();
		
		try {
			DepartmentMapper mapper = openSession.getMapper(DepartmentMapper.class);
			Department deptByIdStep = mapper.getDeptByIdStep(1);
			System.out.println(deptByIdStep);
			System.out.println(deptByIdStep.getEmps());
			
		}finally {
			openSession.close();
		}
	}

延迟加载

	
	
	
		select * from tbl_employee where d_id=#{deptId}
	

　　

6).鉴别器

 

			Department deptByIdStep = mapper.getDeptByIdStep(1);
			System.out.println(deptByIdStep);
			System.out.println(deptByIdStep.getEmps());

	
	
	
	
	
		
	 	
	 	
	 	
	 	
	 	
	 	
	 		
	 		
	 		
	 			 	
			 		
			
			
	 		
	 			
	 			
	 			
	 			
	 		
	 	
	
	
	
		select * from tbl_employee where id=#{id}
	 

3.insert update delete

1)insert

(1)支持自增方式数据库

  若数据库支持自动生成主键的字段（比如 MySQL和 SQL Server）,则可以设置useGeneratedKeys=”true”，然后再把keyProperty 设置到目标属性上

	public void addEmp(Employee employee);

	
	
	
	
	
	
	
		insert into tbl_employee(last_name,email,gender) values(#{lastName},#{email},#{gender})
	

(2)不支持自增方式数据库

  而对于不支持自增型主键的数据库（例如Oracle），则可以使用 selectKey 子元素：selectKey 元素将会首先运行，id 会被设置，然后插入语句会被调用

	public void addEmp(Employee employee);

　　

	
	
		
		
		
		
	
	
		
			
			
			select EMPLOYEES_SEQ.nextval from dual 
			
			 
		
		
		
		
		insert into employees(EMPLOYEE_ID,LAST_NAME,EMAIL) values(#{id},#{lastName},#{email}) 
		
		 
	

2)update

	public void updateEmp(Employee employee);

　　

	
	
		update tbl_employee set last_name=#{lastName},email=#{email},gender=#{gender} where id=#{id}
	

3)delete

	public void deleteEmpById(Integer id);

　　

	
	
		delete from tbl_employee where id=#{id}
	

4)Test

/**
	 * 	测试增删改
	 * 1、mybatis允许增删改直接定义一下的类型返回值	Integer Long Boolean void
	 * 2、我们需要手动提交数据
	 * 		手动提交:sqlSessionFactory.openSession()
	 * 		自动提交:sqlSessionFactory.openSession(true)
	 * @throws IOException 
	 * 
	 */
	@Test
	public void test03() throws IOException {
		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
		SqlSession openSession = sqlSessionFactory.openSession();
		
		try {

			EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
//			测试添加
			Employee employee = new Employee(null, "jerry", "[email protected]", "1");
			mapper.addEmp(employee);
			System.out.println(employee.getId());
			
			//测试修改
//			Employee employee = new Employee(1, "pluto", "[email protected]", "0");
//			mapper.updateEmp(employee);
			
			//测试删除
//			mapper.deleteEmpById(2);
			
			openSession.commit();
		}finally {
			openSession.close();
		}
	}

4.MyBatis参数

1)单个参数

  可以接受基本类型，对象类型，集合类型的值。这种情况MyBatis可直接使用这个参数，不需要经过任何处理

	public Employee getEmpById(Integer id);

　　

select * from tbl_employee where id = #{id}

2)多个参数

  异常：org.apache.ibatis.binding.BindingException: Parameter 'id' not found. Available parameters are [1, 0, param1, param2]

	public Employee getEmpByIdAndLastName(Integer id,String lastName);

　　

select * from tbl_employee where id = #{id} and last_name=#{lastName}

  任意多个参数，都会被MyBatis重新包装成一个Map传入.

  Map的key是param1，param2，0，1…，值就是参数的值.

select * from tbl_employee where id=#{param1} and last_name=#{param2}

(1)命名参数

  参数使用@Param起一个名字，MyBatis就会将这些参数封装进map中，key就是我们自己指定的名字.

- 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

- key：使用@Param注解指定的值|value：参数值

- #{指定的key}取出对应的参数值

　　public Employee getEmpByIdAndLastName(@Param("id")Integer id,@Param("lastName")String lastName);

　　

　　select * from tbl_employee where id=#{id} and last_name=#{lastName}

　　

	@Test
	public void test04() throws IOException {
		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
		//1.获取到sqlSessionFactory但是不会自动提交数据
		SqlSession openSession = sqlSessionFactory.openSession();
		
		try {

			EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
			
			Employee employee = mapper.getEmpByIdAndLastName(1, "plutoo");

			System.out.println(employee);
		}finally {
			openSession.close();
		}
	} 

(2)POJO

  当这些参数属于我们业务POJO时.换句话说，如果多个参数正好是我们业务逻辑的数据模型，我们直接传递POJO.　

	public void getEmpPoJo(Employee employee);

　　

	
	
		update tbl_employee 
        set last_name=#{lastName},email=#{email},gender=#{gender}
        where id=#{id}
	

　

	@Test
	public void test04() throws IOException {
		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
		SqlSession openSession = sqlSessionFactory.openSession(true);
		
		try {

			EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
			
			Employee employee = new Employee(1, "plutoo", "[email protected]", "1");
			mapper.getEmpPoJo(employee);

		}finally {
			openSession.close();
		}
	}

(3)Map

我们也可以封装多个参数为map，直接传递.

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

	public Employee getEmpByMap(Map map);

　　

	
	
		select * from tbl_employee where id=#{id} and last_name=#{lastName}
	

　　

	@Test
	public void test04() throws IOException {
		SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
		//1.获取到sqlSessionFactory但是不会自动提交数据
		SqlSession openSession = sqlSessionFactory.openSession();
		
		try {

			EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
			
//			Employee employee = mapper.getEmpByIdAndLastName(1, "pluto");
			
			Map map = new HashMap<>();
			map.put("id", 1);
			map.put("lastName", "pluto");
			Employee employee = mapper.getEmpByMap(map);
			mapper.getEmpByMap(map);
			
			
			System.out.println(employee);
		}finally {
			openSession.close();
		}
	}

(4)To:

  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

 

(5)参数举例

public Employee getEmp(@Param("id")Integer id,String lastName);
	取值：id==>#{id/param1}   lastName==>#{param2}

public Employee getEmp(Integer id,@Param("e")Employee emp);
	取值：id==>#{param1}    lastName===>#{param2.lastName/e.lastName}

##特别注意：如果是Collection（List、Set）类型或者是数组，
		 也会特殊处理。也是把传入的list或者数组封装在map中。
			key：Collection（collection）,如果是List还可以使用这个key(list)
				数组(array)
				
public Employee getEmpById(List ids);
	取值：取出第一个id的值：   #{list[0]}

(6)查看源码 MyBati怎么处理参数

  参数多时会封装map，为了不混乱，我们可以使用@Param来指定封装时使用的key

public Object getNamedParams(Object[] args) {
    final int paramCount = names.size();
    //1、参数为null直接返回
    if (args == null || paramCount == 0) {
      return null;
     
    //2、如果只有一个元素，并且没有Param注解；args[0]：单个参数直接返回
    } else if (!hasParamAnnotation && paramCount == 1) {
      return args[names.firstKey()];
      
    //3、多个元素或者有Param标注
    } else {
      final Map param = new ParamMap