c++mysqlmysql-x-devapi

How to get value by field name in MYSQL xdevapi 8.0 connector c++


For connector c++ 1.1, in this example, it's quite easy to get values by specifying the column name (or alias name).
But when I upgraded to version 8.0 xdevapi, I found this feature is no longer supported.

#include <mysqlx/xdevapi.h>

using namespace std;
using namespace mysqlx;

Session sess(<server_url>);
auto result = sess.sql("SELECT * FROM student").execute();
Row row = result.fetchOne();
cout << row[0] << endl;         // <- ok
cout << row["ID"] << endl;      // <- can compile but garbage output
cout << row.get("ID") << endl;  // <- cannot compile

I know the column names can be retrieved from result.getColumn(n).getColumnLabel(), but IMO it's useless. A "field" -> "index" mapping can really help the developers.

I'm new to C++, so the following sentenses maybe too naive. Here's the possible ways I guess:


Solution

  • There is no way, at the moment, to get the column value using name.

    A way is, as you suggest, a map with the name / index pair.

    Something like this would work:

    SqlResult sql_res = sess.sql("select * from table").execute();
    
    std::map<std::string, size_t> columns;
    auto fill_columns = [&sql_res, &columns]() -> void
    {
      size_t idx = 0;
      for (auto &el : sql_res.getColumns())
      {
        columns.emplace(std::make_pair(el.getColumnLabel(), idx++));
      }
    };
    
    fill_columns();
    

    And then, using it:

    for(auto row : sql_res)
    {
      std::cout << "a:" << row[columns["a"]] << std::endl;
      std::cout << "b:" << row[columns["b"]] << std::endl;
    }