介紹一個針對C++程序的MySQL訪問庫soci

一直以來，筆者都在不停尋找一種更人性化的數據庫訪問方式（並不是說默認的方式不好，而是有時候的確在模塊化設計中不太方便）。
後來有幸在php中找到codeigniter的ActiveReord，詳細參考這篇文章: 抽離CodeIgniter的數據庫訪問類！
然而c++卻始終用著最原始的方式，昨天趁著項目要用的機會，在網上搜索了好久，總算讓我找到兩套c++的數據庫訪問框架:

   soci
   litesql

兩套代碼我都拿下來看了一下，litesql實現了一套完整的代碼自動生成，功能強大，但是也很重；soci相對要輕量，但是同樣也實現了數據結構到數據庫表的映射。本人還是比較喜歡輕量的東西，所以最終選擇了soci。經過這兩天的試用，感覺非常不錯。

官方的文檔也很詳細，所以這裡就用我寫的單元測試代碼來做一下簡單的講解:
首先創建庫表:

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.簡單的select單條記錄

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();
  }
}
 
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的結果，如果成功則ind會為i_ok，同值sex被賦值；如果失敗則反之

2.簡單的select多條記錄

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();
  }
}

與select單條記錄唯一的區別即，into()的參數是一個vector。其實用多個vector這種方式並不是一個很好的選擇，後面會介紹基於數據結構的方式。

3.簡單的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都有兩個同樣的問題:
a)affect_rows(操作的行數)沒有辦法返回
b)操作的id無法知道，尤其對於insert的主鍵是自增的情況下，無法知道插入的主鍵的值是多少。

update和delete都與insert相似，這裡就不再多說。

接下來是這個框架的很重要的一個特性，即數據庫表與數據結構綁定：

首先我們需要定義一個結構體，並告知soci怎麼讓列名和數據結構的字段對應起來:

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;
    }
  };
}

關於

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

這裡，官方的文檔是是有誤的，我查了好長時間，按照上面的寫法來寫即可。

1.用數據結構來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.用數據結構來進行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();
  }
}

整個就是這樣~~下面是文中代碼文件的下載路徑：
http://code.google.com/p/vimercode/source/browse/#svn%2Ftrunk%2Fsoci_test

另外，雖然python下的mysql訪問也算比較簡單，但還是想知道是否有更Pythonic的庫或接口，如果有朋友知道，歡迎不吝告知。