目录
关于mybatis注解
注解在java中特别常见，mybatis中也支持注解。
mybatis的注解主要功能是：简化mapper.xml文件，简单的sql可以使用注解，而不用在取mapper.xml中写sql了，但是动态sql或者稍微复杂的sql，还得写在mapper.xml中。
mybatis的注解和mapper.xml可以共存。
需要注意：
mybatis配置文件在加载映射文件或者接口的时候，是有点区别的。
1、对于xml文件，可以使用：
<mapper resource="cn/ganlixin/mapper/XxxMapper.xml" /> <mapper url="file:///E:/mappers/XxxMapper.xml" />
2、对于interface，可以使用：
<mapper class="cn.ganlixin.mapper.PersonMapper" /> <package name="cn.ganlixin.mapper" />
初次简单使用mybatis注解示例
创建实体类：cn.ganlixin.pojo.Person.java
package cn.ganlixin.pojo;
import java.io.Serializable;
public class Person implements Serializable{
private int id;
private String name;
private int age;
//省略了无参构造方法、有参构造方法、setter、getter、toString
}
创建interface：cn.ganlixin.mapper.PersonMapper.java
package cn.ganlixin.mapper;
import java.util.List;
import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;
import cn.ganlixin.pojo.Person;
public interface PersonMapper {
@Select("select * from person where id=#{0}")
public Person selectPersonById(int id);
@Select("select * from person")
public List<Person> selectAllPerson();
@Delete("delete from person where id=#{id}")
public int deleteOnePerson(Person person);
@Insert("insert into person (id, name, age) values (default, #{name}, #{age})")
public int addPerson(Person person);
@Update("update person set name=#{name} where id=#{id}")
public int updatePersonName(Person person);
}
修改mybatis配置文件，加载该interface：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties resource="conf/db.properties"></properties>
<settings>
<setting name="logImpl" value="log4J"></setting>
</settings>
<typeAliases>
<package name="cn.ganlixin.pojo" />
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${driver}"></property>
<property name="url" value="${url}"></property>
<property name="username" value="${username}"></property>
<property name="password" value="${password}"></property>
</dataSource>
</environment>
</environments>
<mappers>
<!-- 一次只加载一个interface -->
<!-- <mapper class="cn.ganlixin.mapper.PersonMapper"></mapper> -->
<!-- 一次性加载包下的所有interface -->
<package name="cn.ganlixin.mapper"></package>
</mappers>
</configuration>
进行测试：
package cn.ganlixin.test;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
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 cn.ganlixin.mapper.PersonMapper;
import cn.ganlixin.pojo.Person;
public class TestMybatis {
public static void main(String[] args) {
try {
String resource = "conf/mybatis.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession session = sqlSessionFactory.openSession();
PersonMapper mapper = session.getMapper(PersonMapper.class);
Person person = mapper.selectPersonById(1);
System.out.println(person);
//----------------------------------------------------
List<Person> list = mapper.selectAllPerson();
for (Person p : list) {
System.out.println(p);
}
//----------------------------------------------------
int count = mapper.addPerson(new Person(3, "cccc", 55));
System.out.println(count);
//----------------------------------------------------
Person p = new Person();
p.setId(3);
p.setName("dddd");
count = mapper.updatePersonName(p);
System.out.println(count);
//----------------------------------------------------
count = mapper.deleteOnePerson(p);
System.out.println(count);
//----------------------------------------------------
session.commit();
session.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
利用注解实现指定映射
假设上面的Person实体类中的属性名与数据库中person表中字段名不一一对应时，比如下面这样：
package cn.ganlixin.pojo;
import java.io.Serializable;
public class Person implements Serializable{
private int id1;
private String name1;
private int age1;
//省略了无参构造方法、有参构造方法、setter、getter、toString
}
数据库中person表中的字段是id、name、age，显然与Person类的id1、name1、age1属性不符合。
重新修改PersonMapper接口：
package cn.ganlixin.mapper;
import java.util.List;
import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;
import cn.ganlixin.pojo.Person;
public interface PersonMapper {
@Results(value={
@Result(id=true, column="id", property="id1"),
@Result(column="name", property="name1"),
@Result(column="age", property="age1")
})
@Select("select * from person where id=#{0}")
public Person selectPersonById(int id);
// 需要多次配置@Results
@Results(value={
@Result(id=true, column="id", property="id1"),
@Result(column="name", property="name1"),
@Result(column="age", property="age1")
})
@Select("select * from person")
public List<Person> selectAllPerson();
// 对于增删改，属性作为参数时，传入的参数直接指定准确的属性名，不要用@Result
@Delete("delete from person where id=#{id1}")
public int deleteOnePerson(Person person);
@Insert("insert into person (id, name, age) values (default, #{name1}, #{age1})")
public int addPerson(Person person);
@Update("update person set name=#{name} where id=#{id1}")
public int updatePersonName(Person person);
}
进行测试：
测试代码与上一次的测试代码相同，并且测试结果也与上一次的测试结果相同。
使用注解实现表间关联（1对1）
1对1，就以独生子为例吧，一个father只有一个son。
创建实体类cn.ganlixin.pojo.Son.java
package cn.ganlixin.pojo;
public class Son {
private int id;
private String name;
private int fid; // father id
//省略了无参构造方法、有参构造方法、setter、getter、toString
}
创建实体类cn.ganlixin.pojo.Father.java
package cn.ganlixin.pojo;
public class Father {
private int id;
private String name;
private Son son; // 包含一个son对象
//省略了无参构造方法、有参构造方法、setter、getter、toString
}
创建cn.ganlixin.mapper.FatherMapper.java
package cn.ganlixin.mapper;
import java.util.List;
import org.apache.ibatis.annotations.Select;
import cn.ganlixin.pojo.Father;
public interface FatherMapper {
@Select("select f.id, f.name, s.id `son.id`, s.name `son.name`, s.fid `son.fid` "
+ "from father f left join son s on f.id=s.fid")
public List<Father> selectAll();
}