Mybatis学习
我遇到的问题一个是like ，一个in的语法，下面都有介绍，
like语法 ：比如 like #{name} ，那么这个name提前定以后字符，如： String name="%张%";
in的语法：在写select的时候不应该要 这种标记，他会把不识别foreach，可以把foreach放到这个的外面。我是直接去掉了，可以跑起来程序。这里记录一下，供大家参考,这里的 标记，是为了一些xml一些特殊字符的，比如sql中有'<'这种字符会跟xml中的冲突，这时候要用到这个标记
1 什么是Mybatis
． Mybatis
1 什么是Mybatis
Mybatis 是对 JDBC 的封装，它隐藏了具体的 JDBC的API，它把SQL语句放到了配置文件中，它能自动把不同的输入数据映射到SQL语句的动态参数上，它能自动把SQL语句的执行结果映射为JAVA对象……MyBatis是一个持久化层的框架！
Mybatis 是一个 ORM 框架
可以说 Mybatis 是一个半自动的 ORM 框架,Hibernate是全自动的
2 主配置文件
基本作用就是配置 JDBC 连接的有关信息，比如 URL 、用户名、密码等等
如：
| xmlversion="1.0"encoding="UTF-8"?> DOCTYPEconfiguration PUBLIC"-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<typeAliases> <typeAliastype="org.leadfar.mybatis.Person"alias="Person"/> typeAliases>
<environmentsdefault="development"> <environmentid="development"> <transactionManagertype="JDBC"/> <dataSourcetype="POOLED"> <propertyname="driver"value="com.mysql.jdbc.Driver"/> <propertyname="url"value="jdbc:mysql://localhost/mybatis"/> <propertyname="username"value="root"/> <propertyname="password"value="leadfar"/> dataSource> environment> environments>
<mappers> <mapperresource="org/leadfar/mybatis/PersonMapper.xml"/> mappers> configuration>
|
3 映射文件
基本作用就是编写 SQL 语句，同时给每个 SQL 语句定义一个唯一标识（ID），在程序中通过此ID来调用这条SQL语句。
| xmlversion="1.0"encoding="UTF-8"?> DOCTYPEmapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mappernamespace="org.leadfar.mybatis.Person"> <insertid="insert"parameterType="Person"> insert into t_person(name,age,birthday) values(#{name},#{age},#{birthday}) insert>
mapper > |
4 程序代码
| //声明一个session管理工厂 SqlSessionFactory factory =null; //声明读取器 Reader reader =null; try{ //通过读取器定位到主配置文件 reader = Resources.getResourceAsReader ("SqlMapConfig.xml"); //初始化工厂 factory =newSqlSessionFactoryBuilder().build(reader); }catch(IOException e) { //TODOAuto-generated catch block e.printStackTrace(); } //打开一个会话(类似于jdbc中创建数据库连接) SqlSession session = factory.openSession(); Person p =newPerson(); p.setName("张三"); p.setAge(11); p.setBirthday(newDate()); //进行插入 try{ session.insert("org.leadfar.mybatis.Person.insert", p); //事务提交 session.commit(); System.out.println("保存成功!"); }catch(Exception e) { e.printStackTrace(); //事务回滚 session.rollback(); }finally{ //关闭连接 session.close(); } |
5sql 参数传递
1. 简单参数
| <deleteid="delete"parameterType="int"> delete from t_person where id=#{id} 无所谓写什么都可以à delete> |
2. 多个参数，建议采用 Map 包装
| <selectid="selectLikeNameAndAgeBetween"parameterType="map"resultType="Person"> <includerefid="selectBasic"/>where name like #{name} and age between #{age1} and #{age2} select>
|
| SqlSession session =factory.openSession(); Mapmap =newHashMap(); map .put("name","%张%"); map .put("age1", 0); map .put("age2", 100); List persons=session.selectList(Person.class.getName()+".selectLikeNameAndAgeBetween",map );
System.out.println(((Person)(persons.get(0))).getName()); session.close(); |
6sql 语句块
| <sqlid="selectBasic"> select * from t_person sql> <selectid="selectLikeName"parameterType="string"resultType="Person"> <includerefid="selectBasic"/>where name like #{name} select> |
7 属性名与字段名不匹配
<resultMaptype="Person"id="select-reusltMap">
<resultcolumn="sex"property="gender"/>
resultMap>
<selectid="selectLikeNameAndAgeBetweenResultMap"parameterType="map"resultMap="select-reusltMap">
<includerefid="selectBasic"/>where name like #{name} and age between #{age1} and #{age2}
select>
8 动态sql
8.1 .if
| <selectid="selectIf"parameterType="map"resultType="Person"> select * from t_person <iftest="name !=null"> where name like #{name} if> <iftest="age !=0"> and age=#{age} if> select> |
注：如果 name==null ，则 sql 拼写错误
| <selectid="selectWhere"parameterType="map"resultType="Person"> select * from t_person <where> <iftest="name !=null"> name like #{name} if> <iftest="age !=0"> and age=#{age} if> where> select> |
注 : 加
8.2 .choose
类似于 switch
| <selectid="selectChoose"parameterType="map"resultType="Person"> select * from t_person <choose> <whentest="name!=null"> where name like #{name} when> <otherwise> where name like '%%' otherwise> choose> <iftest="age !=0"> and age=#{age} if> select> |
8.3 .foreach
如 in 操作
| <selectid="selectFor"parameterType="list"resultType="Person"> select * from t_person where id in <foreachcollection="list"item="p"open="("close=")"separator=","> #{p} foreach> select> |
| SqlSession session =factory.openSession(); Listl =newArrayList(); l .add(1); l .add(2); l .add(3); l .add(4); List persons=session.selectList(Person.class.getName()+".selectFor",l );
System.out.println(((Person)(persons.get(1))).getName()); session.close(); |
8.4 $
相当于转义，字符串替换
| <selectid="selectIn"parameterType="map"resultType="Person"> select * from t_person where id in ${instr} select> |
| SqlSession session =factory.openSession();
Map params=newHashMap(); //params.put("name", "%张%"); params.put("instr","(1,2,3,4)"); List persons=session.selectList(Person.class.getName()+".selectIn",params);
System.out.println(((Person)(persons.get(1))).getName()); session.close(); |
另外对于排序时由外部传入某字段
| <selectid="selectOrderBy"parameterType="map"resultType="Person"> select * from t_personorder by${by}
select> |
| SqlSession session =factory.openSession();
Map params=newHashMap(); //params.put("name", "%张%"); params.put("by","age desc"); List persons=session.selectList(Person.class.getName()+".selectOrderBy",params);
System.out.println(((Person)(persons.get(1))).getName()); session.close(); |
9 一对一映射
9.1 简单方法
设 Person 与 Address 是一对一关系
PersonMapper.xml
| <resultMaptype="Person"id="select-resultMap">
<associationproperty="address"select="org.leadfar.mybatis.Address.selectAll"column="id"javaType="Address">
association>
resultMap> |
| <selectid="selectAll"resultMap="select-resultMap"> select * from t_person select> |
AddressMapper.xml
| <selectid="selectAll"parameterType="int"resultType="Address"> select * from t_address where person_id=#{pId} select> |
9.2 解决 N+1 问题
| <selectid="selectAllN1"resultMap="select-resultMapN1"> select a.*,b.id addr_id, b.postCode,b.area from t_person a left join t_address b on a.id=b.person_id select> |
|
<resultMaptype="Person"id="select-resultMapN1"> <idcolumn="id"property="id"/> <resultcolumn="sex"property="gender"/> <resultcolumn="name"property="name"/> <resultcolumn="birthday"property="birthday"/> <resultcolumn="age"property="age"/> <associationproperty="address"column="id"javaType="Address"> <idcolumn="addr_id"property="id"/> <resultcolumn="area"property="area"/> <resultcolumn="postCode"property="postCode"/> association> resultMap> |
6.10 一对多映射
设 Person 和 Car 为一对多关系
| <selectid="selectAllN1"resultMap="select-resultMapN1"> select a.*,b.id addr_id, b.postCode,b.area from t_person a left join t_address b on a.id=b.person_id select> |
|
<resultMaptype="Person"id="select-resultMapN1"> <idcolumn="id"property="id"/> <resultcolumn="sex"property="gender"/> <resultcolumn="name"property="name"/> <resultcolumn="birthday"property="birthday"/> <resultcolumn="age"property="age"/> <associationproperty="address"column="id"javaType="Address"> <idcolumn="addr_id"property="id"/> <resultcolumn="area"property="area"/> <resultcolumn="postCode"property="postCode"/> association>
<collectionproperty="cars"column="id"select="org.leadfar.mybatis.Car.selectByPerson">collection> resultMap> |