单个参数：mybatis不会做特殊处理，
#{参数名}：取出参数值
多个参数：mybatis会做特殊处理。
多个参数会被封装成一个map，
#{}就是从map中获取指定的key的值；
key:param1...paramN或者参数的索引也可以
value:传入参数的值
异常：
org.apache.ibatis.binding.BindingException:
Parameter ‘id‘ not found.
Available parameters are [arg1, arg0, param1, param2]
操作：
方法：public Employee getEmpByIdAndLastName(Integer id,String lastName);
取值：#{id},#{lastName}
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，
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
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
#{属性名}：取出传入的pojo的属性值
Map：
如果多个参数不是业务模型中的数据，没有对应的pojo,为了方便，我们也可以传入map
#{key}取出map中对应的值
TO:
如果多个参数不是业务模型中的数据，但是要经常使用，推荐来编写一个TO（Transfer Object）数据传输对象
Page{
int index;
int size;
}
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=?
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
${}：取出的值直接拼装在SQL语句中；会有安全问题；
大多情况下，我们取参数的值都应该去使用#{}
原生jdbc不支持占位符的地方我们就可以使用${}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};
#{}：更丰富的用法：
规定参数的一些规则：
javaType、jdbcType、mode（存储过程）、numericScale、
resultMap、typeHandler、jdbcTypeName、expression
jdbcType：通常需要在某种特定的条件下被设置：
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Jdbc OTHER
package com.lzr.dao; import com.lzr.bean.Employee; import org.apache.ibatis.annotations.Param; import java.util.Map; /** * @author GGBond * @create 2021-05-22-19:34 */ public interface EmployeeMapper { //public Employee getEmpByIdAndLastName(Integer id,String lastName); public Employee getEmpByMap(Map<String,Object> map); public Employee getEmpByIdAndLastName(@Param("id")Integer id, @Param("lastName")String lastName); public Employee getEmpById(Integer id); public void addEmp(Employee employee); public void updateEmp(Employee employee); public void deleteEmpById(Integer id); }
<?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.lzr.dao.EmployeeMapper"> <!--namespace:名称空间;指定为接口的全类名 id：唯一标识 resultType：返回值类型 #{id}：从传递过来的参数中取出id值 --> <!--public Employee getEmpByMap(Map<String,Object> map);--> <select id="getEmpByMap" resultType="com.lzr.bean.Employee"> select * from tbl_employee where id = #{id} and last_name=#{lastName} </select> <!--public Employee getEmpByIdAndLastName(Integer id,String lastName);--> <select id="getEmpByIdAndLastName" resultType="com.lzr.bean.Employee"> select * from tbl_employee where id = #{id} and last_name=#{lastName} </select> <select id="getEmpById" resultType="com.lzr.bean.Employee" databaseId="mysql"> select * from tbl_employee where id = #{id} </select> <!--public void addEmp(Employee employee);--> <!--parameterType:可以省略 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.getGeneratedKeys(); useGeneratedKeys="true";使用自增主键获取主键值策略 keyProperty:指定对应属性值，也就是mybatis获取到主键值以后，将这个值封装给Javabean的哪个属性 --> <insert id="addEmp" parameterType="com.lzr.bean.Employee" useGeneratedKeys="true" keyProperty="id"> insert into tbl_employee(last_name,email,gender) values(#{lastName},#{email},#{gender}) </insert> <!--public void updateEmp(Employee employee);--> <update id="updateEmp"> update tbl_employee set last_name=#{lastName},email=#{email},gender=#{gender} where id=#{id} </update> <!--public void deleteEmpById(Integer id);--> <delete id="deleteEmpById"> delete from tbl_employee where id=#{id} </delete> </mapper>
/** * 测试增删改 * 1.mybatis允许增删改直接定义以下类型返回值 * Integer,Long,Boolean,void * 2.需要我们手动提交数据 * sqlSessionFactory.openSession();===>手动提交 * sqlSessionFactory.openSession(true);===>自动提交 */ @Test public void test03() 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); //测试添加 Employee employee = new Employee(null, "jerry", "jerry@atguigu.com", "1"); mapper.addEmp(employee); System.out.println(employee.getId()); //测试修改 // Employee employee = new Employee(1, "jerry", "jerry@atguigu.com", "0"); // mapper.updateEmp(employee); //测试删除 //mapper.deleteEmpById(2); //2.手动提交数据 openSession.commit(); }finally { openSession.close(); } } @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); //Employee employee = mapper.getEmpByIdAndLastName(1, "tom"); Map<String,Object> map = new HashMap(); map.put("id",1); map.put("lastName","Tom"); Employee employee = mapper.getEmpByMap(map); System.out.println(employee); }finally { openSession.close(); } }
package com.lzr.bean; import org.apache.ibatis.type.Alias; /** * @author GGBond * @create 2021-05-22-18:17 */ @Alias("emp") public class Employee { private Integer id; private String lastName; private String email; private String gender; public Employee() { super(); } 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 + ‘\‘‘ + ‘}‘; } }
原文：https://www.cnblogs.com/NBYG/p/14807250.html