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<Employee> getEmpsByLastNameLike(String lastName);

	<!-- public List<Employee> getEmpsByLastNameLike(String lastName) -->
	<select id="getEmpsByLastNameLike"	resultType="com.atguigu.mybatis.bean.Employee">
		select * from tbl_employee where last_name like #{lastName}
	</select>

			List<Employee> 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<String,Object> getEmpByIdReturnMap(Integer id);

	<!-- public Map<String,Object> getEmpByIdReturnMap(Integer id) -->
	<!-- resultType:期望从这条语句中返回结果的类全限定名或别名.因为Map类型已经内置了所以我们只需要填map即可 -->
	<select id="getEmpByIdReturnMap" resultType="map">
		select * from tbl_employee where id=#{id}
	</select>

			Map<String, Object> 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<String, Employee> 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<String,Employee> getEmpByLastNameLikeReturnMap(String lastName);
	@MapKey("id")
	public Map<Integer,Employee> getEmpByLastNameLikeReturnMap(String lastName);

	<!-- public Map<Integer,Employee> getEmpByLastNameLikeReturnMap(String lastName) -->
	<select id="getEmpByLastNameLikeReturnMap" resultType="com.atguigu.mybatis.bean.Employee">
		select * from tbl_employee where last_name like #{lastName}
	</select>

//			Map<String, Employee> map = mapper.getEmpByLastNameLikeReturnMap("%r%");
//			System.out.println(map);
			Map<Integer, Employee> 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=plutoo@atguigu.com, gender=1]

关闭:Employee [id=1, lastName=null, email=plutoo@atguigu.com, 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.

	<settings >
		<setting name="mapUnderscoreToCamelCase" value="true"/>
	</settings>

	<!-- public Employee getEmpByid(Integer id) -->
	<!-- resultType:使用了emp是因为我们起了别名@Alias("emp") -->
	<select id="getEmpById"  resultType="emp">
		select * from tbl_employee where id = #{id}
	</select>

	@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=plutoo@atguigu.com, gender=1]

关闭:Employee [id=1, lastName=plutoo, email=plutoo@atguigu.com, 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);

	<settings>
		<!-- <setting name="mapUnderscoreToCamelCase" value="true"/> -->
	</settings>
	<!-- 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 -->
	<resultMap type="com.atguigu.mybatis.bean.Employee" id="MySimpleEmp">
		<!-- 指定主键列的封装规则,id定义主键底层会有优化 -->
		<!-- column:指定列 -->
		<!-- property:指定对应的javaBean属性 -->
		<id column="id" property="id"/>

		<!-- 定义普通封装规则 -->
		<result column="last_name" property="lastName"/>

		<!-- 其他不指定的列会自动封装.只要写resultMap就把全部的映射规则补全 -->
		<result column="email" property="email"/>
		<result column="gender" property="gender"/>
	</resultMap>

	<!-- public Employee getEmpByid(Integer id) -->
	<!-- resultType:使用了emp是因为我们起了别名@Alias("emp") -->
	<!-- resultMap:对外部 resultMap 的命名引用。结果映射是 MyBatis 最强大的特性，如果你对其理解透彻，许多复杂的映射问题都能迎刃而解。  -->
	<!-- resultType 和 resultMap 之间只能同时使用一个 -->
	<select id="getEmpById"  resultMap="MySimpleEmp">
		select * from tbl_employee where id = #{id}
	</select>

	@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);

	<!-- 联合查询:级联属性封装结果集 -->
	<resultMap type="com.atguigu.mybatis.bean.Employee" id="MyDifEmp">
		<id column="id" property="id"/>
		<result column="last_name" property="lastName"/>
		<result column="gender" property="gender"/>
		<result column="did" property="dept.id"/>
		<result column="dept_name" property="dept.departmentName"/>
	</resultMap>

	<!-- public Employee getEmpAndDept(Integer id) -->
	<!-- 场景一:查询Employee的同时查询员工对应的部门 -->
	<!-- 员工与对应部门信息:id  last_name  gender  d_id  did  dept_name  (private Department dept;) -->
	<select id="getEmpAndDept" resultMap="MyDifEmp">
		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}
	</select>

	@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);

	<!-- 使用association定义关联的单个对象的封装规则 -->
	<resultMap type="com.atguigu.mybatis.bean.Employee" id="MyDifEmp2">
		<id column="id" property="id"/>
		<result column="last_name" property="lastName"/>
		<result column="gender" property="gender"/>

		<!-- association:可以指定联合的javaBean对象 -->
		<!-- property:映射到列结果的字段或属性。如果用来匹配的 JavaBean 存在给定名字的属性，那么它将会被使用。 -->
		<!-- javaType:JDBC类型.只需要在可能执行插入、更新和删除的且允许空值的列上指定 JDBC 类型。这是 JDBC 的要求而非 MyBatis 的要求。如果你直接面向 JDBC 编程，你需要对可能存在空值的列指定这个类型。 -->
		<!-- <id column="did" property="id"/>|<id column="id" property="id"/> 这两个property都表示是id,但是column不可一样否则认定为同一个id -->
		<association property="dept" javaType="com.atguigu.mybatis.bean.Department">
			<id column="did" property="id"/>
			<result column="dept_name" property="departmentName"/>
		</association>
	</resultMap>

	<!-- public Employee getEmpAndDept(Integer id) -->
	<!-- 场景一:查询Employee的同时查询员工对应的部门 -->
	<!-- 员工与对应部门信息:id  last_name  gender  d_id  did  dept_name  (private Department dept;) -->
	<select id="getEmpAndDept" resultMap="MyDifEmp2">
		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}
	</select>

	@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

<mapper namespace="com.atguigu.mybatis.dao.DepartmentMapper">

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

</mapper>

(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

<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperPlus">
	<!-- id  last_name  email   gender    d_id -->
	<resultMap type="com.atguigu.mybatis.bean.Employee" id="MyEmpByStep">
		<id column="id" property="id"/>
	 	<result column="last_name" property="lastName"/>
	 	<result column="email" property="email"/>
	 	<result column="gender" property="gender"/>

	 	<!-- association定义关联对象的封装规则 -->
	 	<!-- select:表明当前属性是调用select指定的方法查出的结果 -->
	 	<!-- column:指定将一列的值传给这个方法 -->
	 	<!-- 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.atguigu.mybatis.dao.DepartmentMapper.getDeptById"
	 		column="d_id">
	 	</association>
	</resultMap>

	<!-- 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d_id值去部门表查出部门信息 -->
	<!-- 3、部门设置到员工中 -->
	<!-- public Employee getEmpByIdStep(Integer id) -->
	<select id="getEmpByIdStep" resultMap="MyEmpByStep">
		select * from tbl_employee where id=#{id}
	</select>
</mapper>

(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

	<!-- 使用延迟加载(懒加载) (按需加载) -->
	<!-- 分段查询的基础之上加上两个配置 -->
	<!-- mybatis-config.xml全局配置中在<settings>中添加一下两条 -->
	<!-- <setting name="lazyLoadingEnabled" value="true"/> -->
	<!-- <setting name="aggressiveLazyLoading" value="false"/> -->

	<settings >
		<!--显示的指定我们需要更改的配置的值，即使默认的。防止版本迭代后带来的问题  -->
		<setting name="lazyLoadingEnabled" value="true"/>
		<setting name="aggressiveLazyLoading" value="false"/>
	</settings>

			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<Employee> emps;
}

<mapper namespace="com.atguigu.mybatis.dao.DepartmentMapper">
	<!-- 	private Integer id; private String departmentName; private List<Employee> emps; -->
	<!-- did  dept_name  ||(分割)  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.atguigu.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="emps" ofType="com.atguigu.mybatis.bean.Employee">
			<!-- 定义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>

	@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<Employee> getEmpsByDeptId(Integer deptId);
}

　　

<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperPlus">
	<!-- 场景二:查询部门的时候将部门对应的所有员工信息也查询出来;注释在DepartmentMapper.xml中 -->
	<!-- public List<Employee> getEmpsByDeptId(Integer deptId) -->
	<select id="getEmpsByDeptId" resultType="com.atguigu.mybatis.bean.Employee">
		select * from tbl_employee where d_id=#{deptId}
	</select>
</mapper>

　　

<mapper namespace="com.atguigu.mybatis.dao.DepartmentMapper">
	<!-- collection分段查询  -->
	<resultMap type="com.atguigu.mybatis.bean.Department" id="MyDeptStep">
		<id column="id" property="id"/>
		<id column="dept_name" property="departmentName"/>

		<collection property="emps"
			select="com.atguigu.mybatis.dao.EmployeeMapperPlus.getEmpsByDeptId"
			column="{deptId=id}" fetchType="lazy">
		</collection>
	</resultMap>

	<!-- public Department getDeptByIdStep(Integer id) -->
	<select id="getDeptByIdStep" resultMap="MyDeptStep">
		select id,dept_name departmentName from tbl_dept where id=#{id}
	</select>
</mapper>

　　

	@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

	<!-- 场景二:查询部门的时候将部门对应的所有员工信息也查询出来;注释在DepartmentMapper.xml中 -->
	<!-- public List<Employee> getEmpsByDeptId(Integer deptId) -->
	<select id="getEmpsByDeptId" resultType="com.atguigu.mybatis.bean.Employee">
		select * from tbl_employee where d_id=#{deptId}
	</select>

　　

	<!-- collection分段查询  -->
	<!-- 扩展:需要将多列的值传递 -->
	<!-- 将多列的值封装map传递 -->
	<!-- column="{key1=column1,key2=column2}" -->
	<!-- fetchType="lazy|eager":表示使用延迟加载  	lazy:延迟 eager:立即 -->
	<resultMap type="com.atguigu.mybatis.bean.Department" id="MyDeptStep">
		<id column="id" property="id"/>
		<id column="dept_name" property="departmentName"/>

		<collection property="emps"
			select="com.atguigu.mybatis.dao.EmployeeMapperPlus.getEmpsByDeptId"
			column="{deptId=id}" fetchType="lazy">
		</collection>
	</resultMap>

6).鉴别器

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

	<!-- <discriminator javaType=""></discriminator> -->
	<!-- 鉴别器:一个数据库查询可能会返回多个不同的结果集（但总体上还是有一定的联系的）。 鉴别器元素就是被设计来应对这种情况的 -->
	<!-- 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.atguigu.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 -->
	 	<discriminator javaType="string" column="gender">
	 		<!-- resultType:指定封装的结果类型；不能缺少 -->
	 		<!-- 女生:就把部门信息查询出来 -->
	 		<case value="0" resultType="com.atguigu.mybatis.bean.Employee">
	 			 	<association property="dept"
						select="com.atguigu.mybatis.dao.DepartmentMapper.getDeptById"
						column="d_id">
			 		</association>
			</case>
			<!-- 男生:把last_name这一列的值赋值给email -->
	 		<case value="1" resultType="com.atguigu.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>

	<select id="getEmpByIdStep" resultMap="MyEmpDis">
		select * from tbl_employee where id=#{id}
	</select>

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);

	<!-- public  void addEmp(Employee employee) -->
	<!-- parameterType:将会传入这条语句的参数的类全限定名或别名。这个属性是可选的。 -->
	<!--  获取自增主键的值  -->
	<!-- mysql支持自增主键，自增主键值的获取，mybatis也是利用statement.getGenreatedKeys() -->
	<!-- useGeneratedKeys:使用自增主键获取主键值策略 true|false -->
	<!-- keyProperty:指定对应的主键属性;mybatis获取到主键值以后，将值封装给指定的javaBean属性 -->
	<insert id="addEmp" parameterType="com.atguigu.mybatis.bean.Employee" useGeneratedKeys="true"
		keyProperty="id">
		insert into tbl_employee(last_name,email,gender) values(#{lastName},#{email},#{gender})
	</insert>

(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);

　　

	<!-- 获取非自增主键的值:Oracle不支持自增.Oracle使用序列来模拟自增.每次插入的数据的主键是从序列中拿到的值.-->
	<!-- selectKey:执行查询Key操作 -->
		<!-- keyProperty:指定对应的主键属性;mybatis获取到主键值以后，将值封装给指定的javaBean属性 -->
		<!-- statementType:MyBatis 支持 STATEMENT，PREPARED 和 CALLABLE 类型的映射语句，分别代表 Statement, PreparedStatement 和 CallableStatement 类型。 -->
		<!-- resultType:结果的类型 -->
		<!-- order:可以设置为 BEFORE 或 AFTER。如果设置为 BEFORE，它首先会生成主键，设置 keyProperty 再执行插入语句。如果设置为 AFTER，先执行插入语句，然后 selectKey 中的语句 -->

	<insert id="addEmp" databaseId="oracle">
		<selectKey keyProperty="id" order="BEFORE" resultType="Integer">
			<!-- 编写查询主键的sql语句 -->
			<!-- BEFORE -->
			select EMPLOYEES_SEQ.nextval from dual
			<!-- AFTER：-->
			<!--  select EMPLOYEES_SEQ.currval from dual -->
		</selectKey>

		<!-- 插入时的主键是从序列中拿到的 -->
		<!-- BEFORE:-->
		insert into employees(EMPLOYEE_ID,LAST_NAME,EMAIL) values(#{id},#{lastName},#{email<!-- ,jdbcType=NULL -->})
		<!-- AFTER：-->
		<!-- insert into employees(EMPLOYEE_ID,LAST_NAME,EMAIL) values(employees_seq.nextval,#{lastName},#{email}) -->
	</insert>

2)update

	public void updateEmp(Employee employee);

　　

	<!-- public void updateEmp(Employee employee) -->
	<update id="updateEmp">
		update tbl_employee set last_name=#{lastName},email=#{email},gender=#{gender} where id=#{id}
	</update>

3)delete

	public void deleteEmpById(Integer id);

　　

	<!-- public void deleteEmpById(Integer id) -->
	<delete id="deleteEmpById">
		delete from tbl_employee where id=#{id}
	</delete>

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", "atguigu@atguigu.com", "1");
			mapper.addEmp(employee);
			System.out.println(employee.getId());

			//测试修改
//			Employee employee = new Employee(1, "pluto", "pluto@pluto.com", "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);

　　

	<!-- 	public Employee getEmpPoJo(Integer id,String email) -->
	<select id="getEmpPoJo" resultType="com.atguigu.mybatis.bean.Employee">
		update tbl_employee
        set last_name=#{lastName},email=#{email},gender=#{gender}
        where id=#{id}
	</select>

　

	@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", "plutoo@atguigu.com", "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<String,Object> map);

　　

	<!-- 	public Employee getEmpByMap(Map<String,Object> map) -->
	<select id="getEmpByMap" resultType="com.atguigu.mybatis.bean.Employee">
		select * from tbl_employee where id=#{id} and last_name=#{lastName}
	</select>

　　

	@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<String, Object> 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<Integer> 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<String, Object> param = new ParamMap<Object>();
      int i = 0;

      //4、遍历names集合；{0=id, 1=lastName,2=2}
      for (Map.Entry<Integer, String> entry : names.entrySet()) {

      	//names集合的value作为key;  names集合的key又作为取值的参考args[0]:args【1，"Tom"】:
      	//eg:{id=args[0]:1,lastName=args[1]:Tom,2=args[2]}
        param.put(entry.getValue(), args[entry.getKey()]);

        // add generic param names (param1, param2, ...)param
        //额外的将每一个参数也保存到map中，使用新的key：param1...paramN
        //效果：有Param注解可以#{指定的key}，或者#{param1}
        final String genericParamName = GENERIC_NAME_PREFIX + String.valueOf(i + 1);
        // ensure not to overwrite parameter named with @Param
        if (!names.containsValue(genericParamName)) {
          param.put(genericParamName, args[entry.getKey()]);
        }
        i++;
      }
      return param;
    }
  }
} 

(@Param("id")Integer id,@Param("lastName")String lastName);

ParamNameResolver解析参数封装map的

//names：{0=id, 1=lastName}；构造器的时候就确定好了

流程：

①.获取每个标了param注解的参数的@Param的值:id，lastName赋值给name

②.每次解析一个参数给map中保存信息：（key：参数索引，value：name的值）

- name的值：

- 标注

- param注解：注解的值

- 无标注：

- 全局配置：useActualParamName(jdk1.8):name=参数名

- name=map.size()；相当于当前元素的索引

(7)参数值的获取

#{}：可以获取map中的值或者pojo对象属性的值；

${}：可以获取map中的值或者pojo对象属性的值；　

select * from tbl_employee where id=${id} and last_name=#{lastName}
Preparing: select * from tbl_employee where id=2 and last_name=?

　　

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

　　

①.区别

#{}:是以预编译的形式，将参数设置到sql语句中；PreparedStatement；防止sql注入

${}:取出的值直接拼装在sql语句中；会有安全问题；

大多情况下，我们去参数的值都应该去使用#{}；

原生jdbc不支持占位符的地方我们就可以使用${}进行取值

比如分表、排序。。。；按照年份分表拆分

select * from ${year}_salary where xxx;

select * from tbl_employee order by ${f_name} ${order}

	<!-- 	public Employee getEmpByMap(Map<String,Object> map) -->
	<select id="getEmpByMap" resultType="com.atguigu.mybatis.bean.Employee">
		select * from #{tableName} where id=#{id} and last_name=#{lastName}
	</select>

　　

	<!-- 	public Employee getEmpByMap(Map<String,Object> map) -->
	<select id="getEmpByMap" resultType="com.atguigu.mybatis.bean.Employee">
		select * from ${tableName} where id=#{id} and last_name=#{lastName}
	</select>

　　

@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);
			Map<String, Object> map = new HashMap<>();
			map.put("id", 2);
			map.put("lastName", "plutoo");
			map.put("tableName", "tbl_employee");
			Employee employee = mapper.getEmpByMap(map);
			mapper.getEmpByMap(map);
			System.out.println(employee);
		}finally {
			openSession.close();
		}
	}

②.#{}用法

jdbcType

在我们数据为null的时候，有些数据库可能不能识别mybatis对null的默认处理。比如Oracle(报错)

JdbcType OTHER:无效的类型.因为mybatis对所有的null都映射的是原生Jdbc的OTHER类型，oracle不能正确处理.

全局配置中:jdbcTypeForNull=OTHER；oracle不支持；

两种办法

- #{email,jdbcType=OTHER};

- jdbcTypeForNull=NULL

<setting name="jdbcTypeForNull" value="NULL"/>

参考文档:https://mybatis.org/mybatis-3/zh/sqlmap-xml.html#

https://mybatis.org/mybatis-3/zh/configuration.html#settings

<settings>

<!-- <setting name="mapUnderscoreToCamelCase" value="true"/> -->

</settings>

<!-- 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 -->

<resultMap type="com.atguigu.mybatis.bean.Employee" id="MySimpleEmp">

<!-- 指定主键列的封装规则,id定义主键底层会有优化 -->

<!-- column:指定列 -->

<!-- property:指定对应的javaBean属性 -->

<id column="id" property="id"/>

<!-- 定义普通封装规则 -->

<result column="last_name" property="lastName"/>

<!-- 其他不指定的列会自动封装.只要写resultMap就把全部的映射规则补全 -->

<result column="email" property="email"/>

<result column="gender" property="gender"/>

</resultMap>

<!-- public Employee getEmpByid(Integer id) -->

<!-- resultType:使用了emp是因为我们起了别名@Alias("emp") -->

<!-- resultMap:对外部 resultMap 的命名引用。结果映射是 MyBatis 最强大的特性，如果你对其理解透彻，许多复杂的映射问题都能迎刃而解。  -->

<!-- resultType 和 resultMap 之间只能同时使用一个 -->

<select id="getEmpById"  resultMap="MySimpleEmp">

select * from tbl_employee where id = #{id}

</select>