postgresql的transaction

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从odb的源码中看出了，其实和其它的数据库一样，也都是三条命令。

// file : odb/pgsql/transaction-impl.cxx

// copyright : Copyright (c) 2009-2013 Code Synthesis Tools CC
// license : GNU GPL v2; see accompanying LICENSE file

#include <cassert>

#include <libpq-fe.h>

#include <odb/tracer.hxx>

#include <odb/pgsql/database.hxx>
#include <odb/pgsql/connection.hxx>
#include <odb/pgsql/error.hxx>
#include <odb/pgsql/exceptions.hxx>
#include <odb/pgsql/transaction-impl.hxx>
#include <odb/pgsql/auto-handle.hxx>

namespace odb
{
namespace pgsql
{
transaction_impl::
transaction_impl (database_type& db)
: odb::transaction_impl (db)
{

}

transaction_impl::
transaction_impl (connection_ptr c)
: odb::transaction_impl (c->database (), *c), connection_ (c)
{
}

transaction_impl::
~transaction_impl ()
{
}

void transaction_impl::
start ()
{
// Grab a connection if we don't already have one.
//
if (connection_ == 0)
{
connection_ = static_cast<database_type&> (database_).connection ();
odb::transaction_impl::connection_ = connection_.get ();
}

{
odb::tracer* t;
if ((t = connection_->tracer ()) || (t = database_.tracer ()))
t->execute (*connection_, "BEGIN");
}

auto_handle<PGresult> h (PQexec (connection_->handle (), "begin"));

if (!h || PGRES_COMMAND_OK != PQresultStatus (h))
translate_error (*connection_, h);
}

void transaction_impl::
commit ()
{
// Invalidate query results.
//
connection_->invalidate_results ();

{
odb::tracer* t;
if ((t = connection_->tracer ()) || (t = database_.tracer ()))
t->execute (*connection_, "COMMIT");
}

auto_handle<PGresult> h (PQexec (connection_->handle (), "commit"));

if (!h || PGRES_COMMAND_OK != PQresultStatus (h))
translate_error (*connection_, h);

// Release the connection.
//
connection_.reset ();
}

void transaction_impl::
rollback ()
{
// Invalidate query results.
//
connection_->invalidate_results ();

{
odb::tracer* t;
if ((t = connection_->tracer ()) || (t = database_.tracer ()))
t->execute (*connection_, "ROLLBACK");
}

auto_handle<PGresult> h (PQexec (connection_->handle (), "rollback"));

if (!h || PGRES_COMMAND_OK != PQresultStatus (h))
translate_error (*connection_, h);

// Release the connection.
//
connection_.reset ();
}
}
}

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