本篇文章将研究mybatis 实现oracle主键自增的机制
首先我们看对于同一张student表,对于mysql,sql server,oracle中它们都是怎样创建主键的
在mysql中
create table Student( Student_ID int(6) NOT NULL PRIMARY KEY AUTO_INCREMENT, Student_Name varchar(10) NOT NULL, Student_Age int(2) NOT NULL ); insert into student(student_name,student_age) values('zhangsan',20);
在sql server中
create table Student( Student_ID int primary key identity(1,1), Student_Name varchar2(10) NOT NULL, Student_Age number(2) NOT NULL ); insert into student(student_name,student_age) values('zhangsan',20);
在oracle中
create table Student( Student_ID number(6) NOT NULL PRIMARY KEY, Student_Name varchar2(10) NOT NULL, Student_Age number(2) NOT NULL );
而oracle如果想设置主键自增长,则需要创建序列
CREATE SEQUENCE student_sequence INCREMENT BY 1 NOMAXVALUE NOCYCLE CACHE 10; insert into Student values(student_sequence.nextval,'aa',20);
如果使用了触发器的话,就更简单了
create or replace trigger student_trigger before insert on student for each row begin select student_sequence.nextval into :new.student_id from dual; end student_trigger; /
此时插入的时候触发器会帮你插入id
insert into student(student_name,student_age) values('wangwu',20);
至此,mysql,sql server,oracle中怎样创建表中的自增长主键都已完成。
看一看出oracle的主键自增较mysql和sql sever要复杂些,mysql,sqlserver配置好主键之后,插入时,字段和值一一对应即可,数据库就会完成你想做的,但是在oracle由于多了序列的概念,如果不使用触发器,oracle怎样实现主键自增呢?
<insert id="add" parameterType="Student"> <selectKey keyProperty="student_id" resultType="int" order="BEFORE"> select student_sequence.nextval from dual </selectKey> insert into student(student_id,student_name,student_age) values(#{student_id},#{student_name},#{student_age}) </insert>
或者
<insert id="save" parameterType="com.threeti.to.ZoneTO" > <selectKey resultType="java.lang.Long" keyProperty="id" order="AFTER" > SELECT SEQ_ZONE.CURRVAL AS id from dual </selectKey> insert into TBL_ZONE (ID, NAME ) values (SEQ_ZONE.NEXTVAL, #{name,jdbcType=VARCHAR}) </insert>
MyBatis 插入时候获取自增主键方法有二
以MySQL5.5为例:
方法1:
<insert id="insert" parameterType="Person" useGeneratedKeys="true" keyProperty="id"> insert into person(name,pswd) values(#{name},#{pswd}) </insert>
方法2:
<insert id="insert" parameterType="Person"> <selectKey keyProperty="id" resultType="long"> select LAST_INSERT_ID() </selectKey> insert into person(name,pswd) values(#{name},#{pswd}) </insert>
插入前实体id属性为0;
插入后实体id属性为保存后自增的id;