官方参考文档

本文档内容是自己学习的一个记录，内容来自官方文档
https://www.oschina.net/p/odb-orm?hmsr=aladdin1e1
https://www.codesynthesis.com/products/odb/doc/manual.xhtml#1

ODB是什么？

ODB可以直接把C++的类对象映像成关系型数据库对象。

架构和工作流程

Hello World Example

头文件：

// file      : hello/person.hxx
// copyright : not copyrighted - public domain#ifndef PERSON_HXX
#define PERSON_HXX#include <string>
#include <cstddef> // std::size_t#include <odb/core.hxx>// 定义class person为persistence class
#pragma db object
class person
{
public:person (const std::string& first,const std::string& last,unsigned short age): first_ (first), last_ (last), age_ (age){}const std::string&first () const{return first_;}const std::string&last () const{return last_;}unsigned shortage () const{return age_;}voidage (unsigned short age){age_ = age;}private:// 定义友元函数，odb可以访问私有的默认构造函数friend class odb::access;// 定义默认构造函数用于odb编译器生成support codeperson () {}// 定义数据库的key值，并且这个key是database自生长的#pragma db id autounsigned long id_;std::string first_;std::string last_;unsigned short age_;
};// 定义class person_stat 为 class person的view
// view
#pragma db view object(person)
struct person_stat
{#pragma db column("count(" + person::id_ + ")")std::size_t count;#pragma db column("min(" + person::age_ + ")")unsigned short min_age;#pragma db column("max(" + person::age_ + ")")unsigned short max_age;
};#endif // PERSON_HXX

应用文件：

// file      : hello/driver.cxx
// copyright : not copyrighted - public domain#include <memory>   // std::auto_ptr
#include <iostream>#include <odb/database.hxx>
#include <odb/transaction.hxx>#include "database.hxx" // create_database#include "person.hxx"
#include "person-odb.hxx"using namespace std;
using namespace odb::core;int
main (int argc, char* argv[])
{try{auto_ptr<database> db (create_database (argc, argv));unsigned long john_id, joe_id;// Create a few persistent person objects.//{person john ("John", "Doe", 33);person jane ("Jane", "Doe", 32);person joe ("Joe", "Dirt", 30);transaction t (db->begin ());// Make objects persistent and save their ids for later use.//john_id = db->persist (john);db->persist (jane);joe_id = db->persist (joe);t.commit ();}typedef odb::query<person> query;typedef odb::result<person> result;// Say hello to those over 30.//{transaction t (db->begin ());result r (db->query<person> (query::age > 30));for (result::iterator i (r.begin ()); i != r.end (); ++i){cout << "Hello, " << i->first () << " " << i->last () << "!" << endl;}t.commit ();}// Joe Dirt just had a birthday, so update his age.//{transaction t (db->begin ());auto_ptr<person> joe (db->load<person> (joe_id));joe->age (joe->age () + 1);db->update (*joe);t.commit ();}// Alternative implementation without using the id.///*{transaction t (db->begin ());// Here we know that there can be only one Joe Dirt in our// database so we use the query_one() shortcut instead of// manually iterating over the result returned by query().//auto_ptr<person> joe (db->query_one<person> (query::first == "Joe" &&query::last == "Dirt"));if (joe.get () != 0){joe->age (joe->age () + 1);db->update (*joe);}t.commit ();}*/// Print some statistics about all the people in our database.//{transaction t (db->begin ());// The result of this (aggregate) query always has exactly one element// so use the query_value() shortcut.//person_stat ps (db->query_value<person_stat> ());cout << endl<< "count  : " << ps.count << endl<< "min age: " << ps.min_age << endl<< "max age: " << ps.max_age << endl;t.commit ();}// John Doe is no longer in our database.//{transaction t (db->begin ());db->erase<person> (john_id);t.commit ();}}catch (const odb::exception& e){cerr << e.what () << endl;return 1;}
}

编译，生成Database Support Code

odb -d mysql --generate-query person.hxx  // 仅示例

生成：
person-odb.hxx, person-odb.ixx, person-odb.cxx

编译，生成database schema

odb -d mysql --generate-query --generate-schema person.hxx

这个命令除了生成上面的person-odb.hxx, person-odb.ixx, person-odb.cxx，还会生成
person.sql, which is the database schema for the persistent classes defined in person.hxx.

编译、链接生成应用程序。

• 编译

c++ -c driver.cxx
c++ -c person-odb.cxx

• 链接

c++ -o driver driver.o person-odb.o -lodb-mysql -lodb

• 创建database schema，使用前面生成的.sql文件

mysql --user=odb_test --database=odb_test < person.sql

• 运行程序

./driver --user odb_test --database odb_test