MyBatis增删改查

先把自定义的sql语句亮出来，其中有添加数据并返回主键的sql写法，主要就在于sql语句的书写配置，使用标签<selectKey>z并指定结果类型，映射实体属性，和先后顺序。使用方法就是添加操作完成，mybatis获取自增主键值，并setId()

结果如下，添加之前id为null，添加之后id被赋值。对应测试方法为 public void testInsertReturnId()

mapper.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="student">

	<insert id="insertStduent" parameterType="com.Demo.Entity.Student">
		insert into student(name,age,score) values(#{name},#{age},#{score})
	</insert>
	
	<!-- 使用别名 -->
	<insert id="insertStduentReturnId" parameterType="Student">
		insert into student(name,age,score) values(#{name},#{age},#{score})
		<!-- mysql的自增主键在insert语句之后，所以AFTER。ORACLE数据库的逐渐自增在inert语句之前，所以BEFORE -->
		<selectKey resultType="int" keyProperty="id" order="AFTER">
			select @@identity
		</selectKey>
	</insert>
	
	<delete id="deleteStudent">
		<!-- #{xxx}是占位符，名称随意，参数自动填充 -->
		delete from Student where id = #{xxx}  
	</delete>
	
	<update id="updateStudent">
		update student set name=#{name},age=#{age},score=#{score} where id=#{id}
	</update>
	
	<!-- select结果数据集需要封装到实体类中，需要设置属性resultType -->
	<select id="selectAllStudent" resultType="Student">
		select id,name,age,score from student
	</select>
	
	<select id="selectStudentById" resultType="Student">
		select id,name,age,score from student where id=#{xxx}
	</select>
</mapper>

接口，方法，Utils 和实体类（Util和实体类见https://blog.csdn.net/Yuan52007298/article/details/81413042）

package com.Demo.Dao;

import java.util.List;

import com.Demo.Entity.Student;

public interface StudentDao {
	void insertStudent(Student student);
	void insertStudentReturnId(Student student);
	void deleteStudent(Integer id);
	void updateStudent(Student student);
	List<Student> selectAllStudent();
	Student selectStudentById(Integer id);
}

package com.Demo.Dao;

import java.util.ArrayList;
import java.util.List;

import org.apache.ibatis.session.SqlSession;

import com.Demo.Entity.Student;
import com.Demo.Utils.MyBatisUtil;

public class StudentDaoImpl implements StudentDao {

	@Override
	public void insertStudent(Student student) {

		SqlSession sqlSession = MyBatisUtil.getSqlSession();
		sqlSession.insert("student.insertStduent", student);
		sqlSession.commit();
		sqlSession.close();
	}

	@Override
	public void insertStudentReturnId(Student student) {
		SqlSession sqlSession = MyBatisUtil.getSqlSession();
		sqlSession.insert("student.insertStduentReturnId", student);
		sqlSession.commit();
		sqlSession.close();	
	}

	@Override
	public void deleteStudent(Integer id) {
		SqlSession sqlSession = MyBatisUtil.getSqlSession();
		sqlSession.delete("student.deleteStudent", id);
		sqlSession.commit();
		sqlSession.close();		
	}

	@Override
	public void updateStudent(Student student) {
		SqlSession sqlSession = MyBatisUtil.getSqlSession();
		sqlSession.update("student.updateStudent", student);
		sqlSession.commit();
		sqlSession.close();	
		
	}

	@Override
	public List<Student> selectAllStudent() {
		List<Student> studentList = new ArrayList<>();
		SqlSession sqlSession = MyBatisUtil.getSqlSession();
		studentList = sqlSession.selectList("student.selectAllStudent");
		sqlSession.commit();
		sqlSession.close();	
		return studentList;
	}

	@Override
	public Student selectStudentById(Integer id) {
		Student stu = new Student();
		SqlSession sqlSession = MyBatisUtil.getSqlSession();
		stu = sqlSession.selectOne("selectStudentById", id);
		sqlSession.commit();
		sqlSession.close();	
		return stu;
	}
	
}

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