pqxx重用/重新激活工作事务 [英] pqxx reuse / reactivate a work transaction

问题描述

我想对多个查询和承诺使用pqxx :: work，而 commit 功能阻止我再次使用它。
下面是一个简单的例子：

I want to use a pqxx::work for multiples queries AND commitments, while the commit function prevent me from using it again. Here is a simple example :

pqxx::connection G_connexion("dbname=basetest user=usertest password=1234");
pqxx::work G_work(G_connexion);

int main(int argc, char* argv[]) {
    G_work.exec("insert into test.table1(nom) VALUES('foo');");
    G_work.commit();//until here, no problem
    G_work.exec("insert into test.table1(nom) VALUES('bar');"); //error, transaction already closed
    G_work.commit();
}

当我尝试插入'bar'值时， get a pqxx :: usage_error：执行查询时出错。尝试激活事务< READ COMMITTED>已关闭

When I try to insert the 'bar' value, after the commit, I get a pqxx::usage_error : Error executing query . Attempt to activate transaction<READ COMMITTED> which is already closed

如何在提交更改后避免关闭连接？我可以重置G_work成功相当于G_work = pqxx ::工作（G_connexion），或其他？
另外，一个错误的请求不应该崩溃整个过程，只是一个正在进行中（G_work仍然可以使用失败后）。

How can I avoid to close the connection after I commit the changes ? can i reset G_work with a successing equivalent of G_work=pqxx::work(G_connexion), or other ? Also, one bad request should not crash the entire process, just the one in process (G_work still usable after a failure).

我必须保持相同的变量G_Work，因为它将是从程序中许多地方调用的全局变量。

I have to keep the same variable G_Work because it will be a global variable called from lots of places in the program.

推荐答案

pqxx :: work 只是一个 pqxx :: transaction<> ，它最终从 pqxx :: transaction_base 。

pqxx::work is just a pqxx::transaction<> which eventually gets most of its logic from pqxx::transaction_base.

此类不适用于多个事务。相反，它用于try / catch块中的单个事务。它有一个状态成员变量（ m_Status ），即使在提交后也不会重新初始化。

This class is not intended to serve for several transactions. Instead, it is intended for a single transaction within a try/catch block. It has a state member variable (m_Status) which is never reinitialized, even after a commit.

正常模式是：

{
    pqxx::work l_work(G_connexion);
    try {
        l_work.exec("insert into test.table1(nom) VALUES('foo');");
        l_work.commit();
    } catch (const exception& e) {
        l_work.abort();
        throw;
    }
}

可以说，libpqxx可以在删除时回滚事务避免尝试/ catch完全）但它不。

Arguably, libpqxx could rollback the transaction on deletion (to avoid the try/catch entirely) but it doesn't.

似乎这不适合你的使用模式，因为你想要 G_work 是一个全局变量，可从程序中的多个地方访问。请注意，pqxx :: work不是连接对象的类，而只是一种用C ++异常处理来封装begin / commit / rollback的方法。

It seems that this doesn't fit your usage pattern as you want G_work to be a global variable accessible from several places in your program. Please note that pqxx::work is not the class for connection objects, but just a way to encapsulate begin/commit/rollback with C++ exceptions handling.

然而，libpqxx允许您执行语句外部事务（或至少在libpqxx管理的事务外）。您应该使用 pqxx :: nontransaction 类的实例。

Nevertheless, libpqxx also allows you to execute statement outside transactions (or at least outside libpqxx-managed transactions). You should use instances of pqxx::nontransaction class.

#include "pqxx/nontransaction"

pqxx::connection G_connexion("dbname=basetest user=usertest password=1234");
pqxx::nontransaction G_work(G_connexion);

int f() {
    G_work.exec("insert into test.table1(nom) VALUES('foo');");
    G_work.exec("insert into test.table1(nom) VALUES('bar');");
}

请注意，这相当于：

#include "pqxx/nontransaction"

pqxx::connection G_connexion("dbname=basetest user=usertest password=1234");

int f() {
    pqxx::nontransaction l_work(G_connexion);
    l_work.exec("insert into test.table1(nom) VALUES('foo');");
    l_work.exec("insert into test.table1(nom) VALUES('bar');");
}

最后，无法阻止您管理交易 pqxx :: nontransaction 。如果您想要保存点，则尤其如此。我还建议使用 pqxx :: nontransaction 如果你的事务意味着超过一个函数范围（例如在全局范围）。

Eventually, nothing prevents you to manage transactions with pqxx::nontransaction. This is especially true if you want savepoints. I would also advise using pqxx::nontransaction if your transaction is meant to last beyond a function scope (e.g. at global scope).

#include "pqxx/nontransaction"

pqxx::connection G_connexion("dbname=basetest user=usertest password=1234");
pqxx::nontransaction G_work(G_connexion);

int f() {
    G_work.exec("begin;");
    G_work.exec("insert into test.table1(nom) VALUES('foo');");
    G_work.exec("savepoint f_savepoint;");
    // If the statement fails, rollback to checkpoint.
    try {
        G_work.exec("insert into test.table1(nom) VALUES('bar');");
    } catch (const pqxx::sql_error& e) {
        G_work.exec("rollback to savepoint f_savepoint;");
    }
    G_work.exec("commit;");
}

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