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How to use pqxx::stateless_cursor class from libpqxx?

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?

like image 404
Stéphane Avatar asked Mar 25 '23 06:03


1 Answers

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

    // 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;
like image 154
Stéphane Avatar answered Apr 01 '23 09:04