MyBatis 注解开发+逆向(Generator)
注解开发
最初设计时，MyBatis 是一个 XML 驱动的框架。配置信息是基于 XML 的，而且映射语句也是定义在 XML 中的。随着技术的更新发展,对于开发效率要求也原来越高,特别是一些小型项目;越来越多的框架开始支持注解,
到MyBatis3时,MyBatis对注解有了完善的支持,利用注解可以在一些情况下提高开发效率
但不幸的是，Java 注解的的表达力和灵活性十分有限。尽管很多时间都花在调查、设计和试验上， 最强大的 MyBatis 映射并不能用注解来构建
1. select
接口方法声明:
import com.yyh.pojo.User;
import org.apache.ibatis.annotations.Select;
public interface UserMapper2 {
@Select("select * from kuser where id = #{id}")
public User selectUserByID(int id);
}
测试方法:
@Test
public void selectTest(){
SqlSession session = factory.openSession();
UserMapper2 mapper = session.getMapper(UserMapper2.class);
User user = mapper.selectUserByID(2);
System.out.println(user);
session.close();
}
不要忘记注册这个接口到全局配置中
<mappers>
<mapper class="com.yyh.mapper.UserMapper2"/>
</mappers>
2. sql语句多个参数
接口方法声明:
@Select("select * from kuser where sex = #{sex} and name like '%${name}%'")
public List<User> selectUserBySexAndName(@Param("sex") String sex, @Param("name") String name);
测试方法:
@Test
public void selectTest2(){
SqlSession session = factory.openSession();
UserMapper2 mapper = session.getMapper(UserMapper2.class);
List<User> users = mapper.selectUserBySexAndName("1","张");
System.out.println(users);
session.close();
}
当sql语句需要多个参数时则必须将多个参数打包到一个对象中,通常是POJO或Map,上面的案例中使用了@Param注解本质就是告诉MyBatis有多个参数MyBatis会自动创建一个Map,然后将@Param的值作为Key,然后将Map传给sql,你也可以手动传一个Map
接口方法声明:
@Select("select * from kuser where sex = #{sex} and name like '%${name}%'")
public List<User> selectUserBySexAndName(Map<String,Object> params);
测试方法:
@Test
public void selectTest2(){
SqlSession session = factory.openSession();
UserMapper2 mapper = session.getMapper(UserMapper2.class);
Map<String,Object> params = new HashMap<>(); //存储参数的Map
params.put("sex","1");
params.put("name","张");
List<User> users = mapper.selectUserBySexAndName(params);
System.out.println(users);
session.close();
}
3. insert
接口方法声明:
@Insert("insert into kuser values(null,#{name},#{birthday},#{sex},#{address})")
public int insertUser(User user);
测试方法:
@Test
public void insertTest() {
SqlSession session = factory.openSession();
UserMapper2 mapper = session.getMapper(UserMapper2.class);
User user = new User();
user.setName("jerry");
user.setSex("1");
user.setAddress("亚洲中国");
user.setBirthday(new Date());
mapper.insertUser(user);
session.commit();
session.close();
}
获取自增主键
在@select注解的下方添加@selectKey注解来完成对自增主键的获取
@Insert("insert into kuser values(null,#{name},#{birthday},#{sex},#{address})")
@SelectKey(statement = "select last_insert_id()",keyProperty = "id",resultType = Integer.class,before = false)
public int insertUser(User user);
在执行insert之后执行last_insert_id()函数获取自增值,然后放入对象的某个属性中;
4. update
接口方法声明:
@Update("update kuser set name = #{name}, birthday = #{birthday}, sex = #{sex}, address = #{address} where id = #{id}")
public int updateUser(User u);
// 如果一行太长可以换行些 但是要注意sql语法
测试方法:
@Test
public void updateTest() {
SqlSession session = factory.openSession();
UserMapper2 mapper = session.getMapper(UserMapper2.class);
User user = mapper.selectUserByID(1);
user.setName("王六子");
mapper.updateUser(user);
session.commit();
session.close();
}
5.delete
接口方法声明:
@Delete("delete from kuser where id = #{id}")
public int deleteUserByID(int id);
测试方法:
@Test
public void deleteTest() {
SqlSession session = factory.openSession();
UserMapper2 mapper = session.getMapper(UserMapper2.class);
mapper.deleteUserByID(12);
session.commit();
session.close();
}
6. 动态sql
动态sql指语句中包含逻辑代码,需要先运行逻辑代码,最后产生sql语句,所以需要在注解中告诉MyBatis这是一个动态sql,通过<script>sql....</script>语法来指定;
若想要在sql中使用各种标签则必须添加上述根标签,否则MyBatis会将整体作为sql语句
接口方法声明:
@Select("<script>" +
"select * from kuser" +
"<where>" +
"<if test='name != null'>" +
"and name like '%${name}%'" +
"</if>" +
"<if test='sex != null'>" +
"and sex = #{sex}" +
"</if>" +
"</where>" +
"</script>")
public List<User> searchUserByNameAndSex(@Param("name") String name,@Param("sex") String sex);
测试代码:
@Test
public void dynamicSqlTest(){
SqlSession session = factory.openSession();
UserMapper2 mapper = session.getMapper(UserMapper2.class);
List<User> users = mapper.searchUserByNameAndSex(null,null);
// List<User> users = mapper.searchUserByNameAndSex("张",null);
// List<User> users = mapper.searchUserByNameAndSex("张", "2");
System.out.println(users);
session.close();
}
7.结果映射(ResultMap)
1.自定义字段与属性对应关系
准备工作:将数据库中的name字段修改为username,然后我们通过ResultMap来手动映射name字段
接口方法声明:
@Select("select *from kuser where username = #{name}")
@Results({
@Result(id = true,column = "id",property = "id"),
@Result(column = "username",property = "name"),
})
public User selectUserByName(String name);
测试代码省略..
重复使用Results
可以发现,MyBatis默认会自动映射所有字段和属性匹配的数据,另外id表示是否为主键字段,默认为false
强调:Results可以位于对应方法的上面或下面,但是无法跨域其他方法,默认只对当前方法有效,如果需要重复使用则需要为其指定id
接口方法声明:
//定义
@Results(id="map1",value = {
@Result(id = true,column = "id",property = "id"),
@Result(column = "username",property = "name"),
})
//.....中间必须间隔其他方法不能立即应用到某个ResultMap
使用:
@Select("select *from kuser where username = #{name}")
//通过@ResultMap注解 并传入id来使用
@ResultMap("map1")
public User selectUserByName(String name);
注意:
@Results的定义不能和使用它的@ResultMap一起出现,既然是重复使用的,建议统一放在接口的最上面,
如果是当前要使用的并且要重用,直接使用Results即可,不需要在下面添加ResultMap就像下面这样:
@Select("select *from kuser where username = #{name}")
@Results(id="map1",value = {
@Result(id = true,column = "id",property = "id"),
@Result(column = "username",property = "name"),
})
public User selectUserByName(String name);
2.关联查询
一对多关联
//实现根据用户姓名查询用户信息和订单信息
@Select("select *from kuser where username = #{name}")
@Results(value = {
@Result(id = true,column = "id",property = "id"),
@Result(column = "username",property = "name"),
//一对多关联,指定子查询语句的方法名称(全限定名称)column指定传给子查询的参数
@Result(column = "id",property = "orders",many = @Many(select = "com.yyh.mapper.UserMapper2.selectOrdersByID")),
})
public User selectUserAdnOrdersByUserName(String name);
//注意这里的条件字段时order表中的字段
@Select("select *from Orders where user_id = #{id}")
public List<Order> selectOrdersByID(int id);
一对一关联 只需要修改属性名称和注解名称即可:
@Select("select *from orders where id = #{id}")
@Results(value = {
@Result(id = true,column = "id",property = "id"),
@Result(column = "user_id",property = "user" ,one = @One(select = "com.yyh.mapper.UserMapper2.selectUserByID")),
})
public Order selectOrderByID(int id);
逆向工程(generator)
generator翻译为生成器,是MyBatis开源的一个插件,可以从数据库获取表信息,自动生成Mapper.xml,POJO,以及Mapper接口
但问题是,MyBatis不可能完全清楚我们的业务需求,所以其自动生成的sql只能满足基本的CRUD操作,而无法帮助我们进行连表操作,(当然包括带有条件的CRUD)
使用步骤
1.使用Maven添加generator插件
<build>
<plugins>
<plugin>
<groupId>org.mybatis.generator</groupId>
<artifactId>mybatis-generator-maven-plugin</artifactId>
<version>1.3.7</version>
<configuration>
<!-- 是否覆盖已存在的接口和POJO该配置不包括Mapper
若为False将会生成版本记录-->
<overwrite>true</overwrite>
</configuration>
</plugin>
</plugins>
</build>
2.创建数据库配置文件,位于resource下名为jdbc.properties
driver = com.mysql.jdbc.Driver
url = jdbc:mysql:///HMDB?serverTimezone=Asia/Shanghai&characterEncoding=utf8&useSSL=false
user = root
password = admin
location = /Users/jerry/.m2/repository/mysql/mysql-connector-java/5.1.44/mysql-connector-java-5.1.44.jar
3.创建配置文件,位于resource下名为generatorConfig.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE generatorConfiguration
PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
"http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
<generatorConfiguration>
<!--导入属性配置-->
<properties resource="jdbc.properties"></properties>
<!--指定特定数据库的jdbc驱动jar包的位置-->
<classPathEntry location="${location}"/>
<context id="default" targetRuntime="MyBatis3">
<!-- optional，旨在创建class时，对注释进行控制 -->
<commentGenerator>
<property name="suppressDate" value="true"/>
<property name="suppressAllComments" value="true"/>
</commentGenerator>
<!--jdbc的数据库连接 -->
<jdbcConnection
driverClass="${driver}" connectionURL="${url}" userId="${user}" password="${password}">
</jdbcConnection>
<!-- 非必需，类型处理器，在数据库类型和java类型之间的转换控制-->
<javaTypeResolver>
<property name="forceBigDecimals" value="false"/>
</javaTypeResolver>
<!--Model模型生成器,用来生成含有主键key的类，记录类 以及查询Example类
targetPackage 指定生成的model生成所在的包名
targetProject 指定在该项目下所在的路径 -->
<javaModelGenerator targetPackage="com.yyh.pojo" targetProject="src/main/java">
<!-- 是否允许子包，即targetPackage.schemaName.tableName -->
<property name="enableSubPackages" value="false"/>
<!-- 是否对model添加 构造函数 -->
<property name="constructorBased" value="true"/>
<!-- 是否对类CHAR类型的列的数据进行trim操作 -->
<property name="trimStrings" value="true"/>
<!-- 建立的Model对象是否 不可改变 即生成的Model对象不会有 setter方法，只有构造方法 -->
<property name="immutable" value="false"/>
</javaModelGenerator>
<!--mapper映射文件生成所在的目录 为每一个数据库的表生成对应的SqlMap文件 -->
<sqlMapGenerator targetPackage="com.yyh.dao"
targetProject="src/main/resources">
<property name="enableSubPackages" value="false"/>
</sqlMapGenerator>
<!--mapper接口文件生成所在的目录 为每一个数据库的表生成对应的接口文件 -->
<javaClientGenerator type="XMLMAPPER" targetPackage="com.yyh.dao" targetProject="src/main/java">
<!-- enableSubPackages:是否让schema(数据库名称)作为包的后缀 -->
<property name="enableSubPackages" value="false"/>
</javaClientGenerator>
<!--指定需要生成的表-->
<table tableName="category"></table>
<table tableName="orders"></table>
<table tableName="products"></table>
<table tableName="kuser"></table>
</context>
</generatorConfiguration>
若自定义配置文件名称则需要在pom中指定
<build>
<plugins>
<plugin>
<groupId>org.mybatis.generator</groupId>
<artifactId>mybatis-generator-maven-plugin</artifactId>
<version>1.3.7</version>
<configuration>
<!-- 自定义配置文件 相对于项目根目录-->
<configurationFile>src/main/resources/aaaa.xml</configurationFile>
<overwrite>true</overwrite>
</configuration>
</plugin>
</plugins>
</build>
3.运行generator
可在idea右侧的maven菜单中双击执行mybatis-generator:generate
也可利用maven命令执行:mybatis-generator:generate
4.条件查询的使用查看POJO包,会发现每个POJO对应了一个Example,这是什么呢?
generator的目标是尽可能的帮我们减少sql的编写,如果只能进行简单的CRUD那意义不大,于是generator使用了一套Example来帮助我们用OOP(面向对象)的方式来完成SQL中的条件拼接
其设计思想是将条件看做是一个对象,该对象包含了SQL中常见的比较,逻辑运算等......打开文件你会发现其本质就是帮我们拼接响应的sql符号和关键字
5.CRUD案例
import com.yyh.dao.KuserMapper;
import com.yyh.pojo.Kuser;
import com.yyh.pojo.KuserExample;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
public class GeneratorTest {
private SqlSessionFactory factory;
@Before
public void init() throws IOException {
//获取的工厂构造器
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
//加载配置文件
InputStream stream = Resources.getResourceAsStream("mybatis-config.xml");
//获得会话工厂
factory = builder.build(stream);
}
//查询
@Test
public void test(){
SqlSession session = factory.openSession();
KuserMapper mapper = session.getMapper(KuserMapper.class);
Kuser kuser = mapper.selectByPrimaryKey(1);
System.out.println(kuser.getSex());
System.out.println(kuser.getAddress());
System.out.println(kuser.getBirthday());
System.out.println(kuser.getUsername());
}
//修改
@Test
public void test2(){
SqlSession session = factory.openSession();
KuserMapper mapper = session.getMapper(KuserMapper.class);
Kuser kuser = mapper.selectByPrimaryKey(1);
kuser.setUsername("XXXXXXXXX");
mapper.updateByPrimaryKey(kuser);
session.commit();
}
//添加
@Test
public void test3(){
SqlSession session = factory.openSession();
KuserMapper mapper = session.getMapper(KuserMapper.class);
Kuser auser = new Kuser();
auser.setUsername("jack");
auser.setAddress("北京东城");
mapper.insert(auser);
session.commit();
}
//删除
@Test
public void test4() {
SqlSession session = factory.openSession();
KuserMapper mapper = session.getMapper(KuserMapper.class);
mapper.deleteByPrimaryKey(13);
session.commit();
}
//and条件
@Test
public void test5() {
SqlSession session = factory.openSession();
KuserMapper mapper = session.getMapper(KuserMapper.class);
KuserExample kuserExample = new KuserExample();
KuserExample.Criteria criteria = kuserExample.createCriteria();
criteria.andBirthdayIsNotNull();
criteria.andUsernameLike("%张%");
List<Kuser> kusers = mapper.selectByExample(kuserExample);
System.out.println(kusers);
}
// or条件
@Test
public void test6() {
SqlSession session = factory.openSession();
KuserMapper mapper = session.getMapper(KuserMapper.class);
KuserExample kuserExample = new KuserExample();
//创建一个条件对象,可以包含n个and
KuserExample.Criteria criteria1 = kuserExample.createCriteria();
criteria1.andUsernameLike("%张%");
//创建一个条件对象可以包含n个and,且前面添加or关键字
KuserExample.Criteria criteria2 = kuserExample.or();
criteria2.andBirthdayIsNull();
//最终的意思是 名字带有张的 或者生日为空的; 具体查看生产的sql即可
List<Kuser> kusers = mapper.selectByExample(kuserExample);
System.out.println(kusers);
}
}
注意:重新生成的Mapper文件时不会不会覆盖之前的Mapper,而是会直接在里面添加sql导致id冲突,所以重新生成mapper时一定要手动删除已存在的mapper
