Mybatis注解操作数据库CURD示例及Param注解注意事项

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    Mybatis使用注解操作数据库CURD的简单示例（这里只演示注解所需要的相关东西，其它项目配置及文件见文章：http://www.04007.cn/article/888.html 和 http://www.04007.cn/article/892.html ）。本文地址:http://www.04007.cn/article/894.html,未经许可,不得转载.

    关于@param() 注解本文地址:http://www.04007.cn/article/894.html,未经许可,不得转载.

    1.引用类型参数不用加param注解, 基本类型在参数只有一个的话，可以加上，可以不加。如果有多个参数的话就需要加上。建议统一不管是几个基本类型参数都加上。加上param后，SQL中只能引用param()中设定的参数名。本文地址:http://www.04007.cn/article/894.html,未经许可,不得转载.

    2.在SQL语句中引用字段的时候可以使用#{}或${}，但建议尽量使用#{}。#{}:表示一个占位符号，可以实现preparedStatement占位，自动进行java类型和jdbc类型转换，可有效防止sql注入。而${}:表示拼接sql字符串，${}传入的内容拼接在sql中但不进行jdbc类型转换，安全性不如#{}。因此尽量使用#{}本文地址:http://www.04007.cn/article/894.html,未经许可,不得转载.

    AreaMapper类文件代码如下：包括CURD各方法的定义，及SQL注解：本文地址:http://www.04007.cn/article/894.html,未经许可,不得转载.

//AreaMapper类代码
package com.kermit.dao;

import com.kermit.pojo.Area;
import org.apache.ibatis.annotations.*;
import java.util.List;

public interface AreaMapper {

    @Select("select * from area")
    public List<Area> getList();

    @Select("select * from area where id=#{id} limit 1")
    public Area getOne(@Param("id") int id);

    @Insert("insert into area(city, area, stat) values(#{city}, #{area}, #{stat})")
    public int insertArea(Area area);

    @Update("update area set city=#{city},area=#{area},stat=#{stat} where id=#{id}")
    public int updateArea(Area area);

    @Delete("delete from area where id= #{aid}")
    public int deleteArea(@Param("aid") int id);

}

 //junit测试代码如下：
 import com.kermit.dao.AreaMapper;
import com.kermit.pojo.Area;
import com.kermit.utils.MybatisConn;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.io.IOException;
import java.util.List;

public class TestMybatis {

    @Test
    public void test1() throws IOException {

        SqlSession sqlSession = MybatisConn.getSqlsession();
        AreaMapper mapper = sqlSession.getMapper(AreaMapper.class);

        //增加一条记录
        int rsInsert = mapper.insertArea(new Area(0,"上海","闵行区", 1));
        System.out.println("增加结果："+rsInsert+"--");

        //删除一条记录
        int rsDelete = mapper.deleteArea(30);
        System.out.println("删除结果："+rsDelete+"--");
        int rsDelete2 = mapper.deleteArea(30);
        System.out.println("再删除返回结果："+rsDelete2+"--");

        //更改一条记录
        int rsUpdate =  mapper.updateArea(new Area(1, "北京", "海淀区", 1));
        System.out.println("更新结果："+rsUpdate+"--");

        //查询多条记录
        List<Area> arealist = (List<Area>) mapper.getList();
        System.out.println("查询结果如下：");
        for(Area area: arealist){
            System.out.println(area);
        }

        //查询一条记录
        Area area =  mapper.getOne(1);
        System.out.println("查询单条结果如下：");
        System.out.println(area);
        System.out.println(area.getCity());

        sqlSession.close();
    }
}

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示例中使用Mybatis如果我们只需要得到一条查询结果，如方法中的getOne，我们只需要指定其返回类型为Area，而不是List，即可实现。程序执行结果如下(logImpl为STDOUT_LOGGING）：本文地址:http://www.04007.cn/article/894.html,未经许可,不得转载.

......Logging initialized using 'class org.apache.ibatis.logging.stdout.StdOutImpl' adapter.
PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
Opening JDBC Connection
Created connection 1899223686.
Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@7133da86]
==>  Preparing: insert into area(city, area, stat) values(?, ?, ?) 
==> Parameters: 上海(String), 闵行区(String), 1(Integer)
<==    Updates: 1
增加结果：1--
==>  Preparing: delete from area where id= ? 
==> Parameters: 30(Integer)
<==    Updates: 1
删除结果：1--
==>  Preparing: delete from area where id= ? 
==> Parameters: 30(Integer)
<==    Updates: 0
再删除返回结果：0--
==>  Preparing: update area set city=?,area=?,stat=? where id=? 
==> Parameters: 北京(String), 海淀区(String), 1(Integer), 1(Integer)
<==    Updates: 1
更新结果：1--
==>  Preparing: select * from area 
==> Parameters: 
<==    Columns: id, city, area, stat
<==        Row: 1, 北京, 海淀区, 1
<==        Row: 35, 北京, 东城区, 1
<==        Row: 18, 厦门, 思明区, 1
<==        Row: 37, 上海, 闵行区, 1
<==        Row: 39, 上海, 闵行区, 1
<==      Total: 5
查询结果如下：
Area(id=1, city=北京, area=海淀区, stat=1)
Area(id=35, city=北京, area=东城区, stat=1)
Area(id=18, city=厦门, area=思明区, stat=1)
Area(id=37, city=上海, area=闵行区, stat=1)
Area(id=39, city=上海, area=闵行区, stat=1)
==>  Preparing: select * from area where id=? limit 1 
==> Parameters: 1(Integer)
<==    Columns: id, city, area, stat
<==        Row: 1, 北京, 海淀区, 1
<==      Total: 1
查询单条结果如下：
Area(id=1, city=北京, area=海淀区, stat=1)
北京
Rolling back JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@7133da86]
Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@7133da86]
Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@7133da86]
Returned connection 1899223686 to pool.

Process finished with exit code 0

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