介绍一个针对C++程序的MySQL访问库soci

一直以来，笔者都在不停寻找一种更人性化的数据库访问方式（并不是说默认的方式不好，而是有时候的确在模块化设计中不太方便）。
后来有幸在php中找到codeigniter的ActiveReord，详细参考这篇文章: 抽离CodeIgniter的数据库访问类！
然而c++却始终用着最原始的方式，昨天趁着项目要用的机会，在网上搜索了好久，总算让我找到两套c++的数据库访问框架:

soci
litesql

两套代码我都拿下来看了一下，litesql实现了一套完整的代码自动生成，功能强大，但是也很重；soci相对要轻量，但是同样也实现了数据结构到数据库表的映射。本人还是比较喜欢轻量的东西，所以最终选择了soci。经过这两天的试用，感觉非常不错。

官方的文档也很详细，所以这里就用我写的单元测试代码来做一下简单的讲解:
首先创建库表:

create database soci;CREATE TABLE `tb_test` ( `id` int(11) NOT NULL auto_increment, `name` varchar(32) default "", `sex` int(11) default 0, PRIMARY KEY (`id`), UNIQUE KEY `name` (`name`)); create database soci;CREATE TABLE `tb_test` ( `id` int(11) NOT NULL auto_increment, `name` varchar(32) default "", `sex` int(11) default 0, PRIMARY KEY (`id`), UNIQUE KEY `name` (`name`));

1.简单的select单条记录

TEST(soci,select_one){  try  {    session sql(mysql/' target='_blank'>mysql, "host=localhost db=soci user=dantezhu");    indicator ind;    string name = "dandan";    int sex;    sql << "select sex from tb_test where name = :name",      into(sex, ind), use(name);    ASSERT_EQ(ind, i_ok) << name;  }  catch (exception const &e)  {    FAIL()<<e.what();  }} TEST(soci,select_one){  try  {    session sql(MySQL, "host=localhost db=soci user=dantezhu");    indicator ind;     string name = "dandan";    int sex;    sql << "select sex from tb_test where name = :name",      into(sex, ind), use(name);     ASSERT_EQ(ind, i_ok) << name;  }  catch (exception const &e)  {    FAIL()<<e.what();  }}

select的结果，如果成功则ind会为i_ok，同值sex被赋值；如果失败则反之

2.简单的select多条记录

TEST(soci,select_multi2){  try  {    session sql(mysql, "db=soci user=dantezhu");    indicator ind;    int count;    sql << "select count(*) from tb_test", into(count, ind);    ASSERT_EQ(ind, i_ok) << count;    if (count == 0)    {      SUCCEED();      return;    }    int sex = 1;    vector<string> vec_name(count);    vector<int> vec_sex(count);    sql << "select name,sex from tb_test where sex = :sex",      into(vec_name), into(vec_sex), use(sex);  }  catch (exception const &e)  {    FAIL()<<e.what();  }} TEST(soci,select_multi2){  try  {    session sql(mysql, "db=soci user=dantezhu");    indicator ind;     int count;    sql << "select count(*) from tb_test", into(count, ind);    ASSERT_EQ(ind, i_ok) << count;     if (count == 0)    {      SUCCEED();      return;    }     int sex = 1;    vector<string> vec_name(count);    vector<int> vec_sex(count);    sql << "select name,sex from tb_test where sex = :sex",      into(vec_name), into(vec_sex), use(sex);  }  catch (exception const &e)  {    FAIL()<<e.what();  }}

与select单条记录唯一的区别即，into()的参数是一个vector。其实用多个vector这种方式并不是一个很好的选择，后面会介绍基于数据结构的方式。

3.简单的insert

TEST(soci,insert_exist){  try  {    session sql(mysql, "db=soci user=dantezhu");    string name = "dandan";    int sex = 1;    sql << "insert into tb_test(name, sex) values(:name, :sex)",      use(name), use(sex);  }  catch (exception const &e)  {    SUCCEED()<<e.what();  }} TEST(soci,insert_exist){  try  {    session sql(mysql, "db=soci user=dantezhu");     string name = "dandan";    int sex = 1;     sql << "insert into tb_test(name, sex) values(:name, :sex)",      use(name), use(sex);  }  catch (exception const &e)  {    SUCCEED()<<e.what();  }}

insert，update，delete都有两个同样的问题:
a)affect_rows(操作的行数)没有办法返回
b)操作的id无法知道，尤其对于insert的主键是自增的情况下，无法知道插入的主键的值是多少。

update和delete都与insert相似，这里就不再多说。

接下来是这个框架的很重要的一个特性，即数据库表与数据结构绑定：

首先我们需要定义一个结构体，并告知soci怎么让列名和数据结构的字段对应起来:

struct Person{  int id;  std::string name;  int sex;};namespace soci{  template<> struct type_conversion<Person>  {    typedef values base_type;    static void from_base(values const & v, indicator /* ind */, Person & p)    {      p.id = v.get<int>("id");      p.name = v.get<std::string>("name");      p.sex = v.get<int>("sex");    }    static void to_base(const Person & p, values & v, indicator & ind)    {      v.set("id", p.id);      v.set("name", p.name);      v.set("sex", p.sex);      ind = i_ok;    }  };} struct Person{  int id;  std::string name;  int sex;}; namespace soci{  template<> struct type_conversion<Person>  {    typedef values base_type;    static void from_base(values const & v, indicator /* ind */, Person & p)    {      p.id = v.get<int>("id");      p.name = v.get<std::string>("name");      p.sex = v.get<int>("sex");    }    static void to_base(const Person & p, values & v, indicator & ind)    {      v.set("id", p.id);      v.set("name", p.name);      v.set("sex", p.sex);      ind = i_ok;    }  };}

关于

template<> struct type_conversion<Person> template<> struct type_conversion<Person>

这里，官方的文档是是有误的，我查了好长时间，按照上面的写法来写即可。

1.用数据结构来select

TEST(soci,select_obj_one){  try  {    session sql(mysql, "db=soci user=dantezhu");    indicator ind;    int count;    sql << "select count(*) from tb_test", into(count, ind);    ASSERT_EQ(ind, i_ok) << count;    string name = "dandan";    Person p;    sql << "select id,name,sex from tb_test where name = :name",      into(p, ind), use(name);    ASSERT_EQ(ind, i_ok) << name;    if (sql.got_data())    {      cout<< p.id         << ","         << p.name         << ","         << p.sex         << endl;    }  }  catch (exception const &e)  {    FAIL()<<e.what();  }} TEST(soci,select_obj_one){  try  {    session sql(mysql, "db=soci user=dantezhu");    indicator ind;     int count;    sql << "select count(*) from tb_test", into(count, ind);    ASSERT_EQ(ind, i_ok) << count;     string name = "dandan";    Person p;    sql << "select id,name,sex from tb_test where name = :name",      into(p, ind), use(name);     ASSERT_EQ(ind, i_ok) << name;     if (sql.got_data())    {      cout<< p.id         << ","         << p.name         << ","         << p.sex         << endl;    }   }  catch (exception const &e)  {    FAIL()<<e.what();  }}

2.用数据结构来进行insert

TEST(soci,insert_obj_noexist){  try  {    session sql(mysql, "db=soci user=dantezhu");    Person p = {      0,      "niuniu",      2    };    sql << "insert into tb_test(name, sex) values(:name, :sex)",      use(p);  }  catch (exception const &e)  {    FAIL()<<e.what();  }} TEST(soci,insert_obj_noexist){  try  {    session sql(mysql, "db=soci user=dantezhu");     Person p = {      0,      "niuniu",      2    };     sql << "insert into tb_test(name, sex) values(:name, :sex)",      use(p);  }  catch (exception const &e)  {    FAIL()<<e.what();  }}

整个就是这样~~下面是文中代码文件的下载路径：
http://code.google.com/p/vimercode/source/browse/#svn%2Ftrunk%2Fsoci_test

另外，虽然python/' target='_blank'>python下的mysql访问也算比较简单，但还是想知道是否有更Pythonic的库或接口，如果有朋友知道，欢迎不吝告知。