如何使用pqxx :: stateless_cursor类从libpqxx？ [英] How to use pqxx::stateless_cursor class from libpqxx?

问题描述

我正在学习libpqxx，C ++ API到PostgreSQL。我想使用pqxx :: stateless_cursor类，但1）我发现Doxygen输出在这种情况下没有帮助，和2）pqxx.org网站已经下来了一段时间了。

任何人都知道如何使用它？

我相信这是我如何构建一个：

  pqxx :: stateless_cursor< pqxx :: cursor_base :: read_only，pqxx :: cursor_base :: owned> 
 cursor（work，SELECT * FROM mytable，？，？）; 
  

最后两个parms称为 cname 保留，但未记录。

一旦创建光标，我将如何使用它

感谢@Eelke对<$ c的评论$ c> cname 和 hold 。

我想出了如何使pqxx： ：stateless_cursor工作。我不知道是否有一个更清洁或更明显的方式，但这里是一个例子：

  pqxx ::工作）; 
 pqxx :: stateless_cursor< pqxx :: cursor_base :: read_only，pqxx :: cursor_base :: owned> 
 cursor（work，SELECT * FROM mytable，mycursor，false）; 
 
 for（size_t idx = 0; true; idx ++）
 {
 pqxx :: result result = cursor.retrieve（idx，idx + 1）; 
 if（result.empty（））
 {
 //没有剩下的东西可以读取
 break; 
} 
 
 //在这个例子中使用result执行一个包含单个
 //行的操作，因为我们告诉游标到
 //检索行＃ idx（包含）到idx + 1（不包含）。 
 std :: cout<< result [0] [name] .as< std :: string>（）< std :: endl; 
} 
  

I'm learning libpqxx, the C++ API to PostgreSQL. I'd like to use the pqxx::stateless_cursor class, but 1) I find the Doxygen output unhelpful in this case, and 2) the pqxx.org website has been down for some time now.

Anyone know how to use it?

I believe this is how I construct one:

pqxx::stateless_cursor <pqxx::cursor_base::read_only, pqxx::cursor_base::owned>
    cursor( work, "SELECT * FROM mytable", ?, ? );

The last two parms are called cname and hold, but are not documented.

And once the cursor is created, how would I go about using it in a for() loop to get each row, one at a time?

解决方案

Thanks @Eelke for the comments on cname and hold.

I figured out how to make pqxx::stateless_cursor work. I have no idea if there is a cleaner or more obvious way but here is an example:

pqxx::work work( conn );
pqxx::stateless_cursor<pqxx::cursor_base::read_only, pqxx::cursor_base::owned>
    cursor( work, "SELECT * FROM mytable", "mycursor", false );

for ( size_t idx = 0; true; idx ++ )
{
    pqxx::result result = cursor.retrieve( idx, idx + 1 );
    if ( result.empty() )
    {
        // nothing left to read
        break;
    }

    // Do something with "result" which contains a single
    // row in this example since we told the cursor to
    // retrieve row #idx (inclusive) to idx+1 (exclusive).
    std::cout << result[ 0 ][ "name" ].as<std::string>() << std::endl;
}

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