Json workflow

[ShuP1]

How well do this work with tao::json ?

For example, how to do a "basic" insert returning id then select back.

CREATE TABLE my_table {
    id serial NOT NULL,
    content jsonb NOT NULL,
    CONSTRAINT my_table_pk PRIMARY KEY (id)
}

With the json doc sample

struct my_type
{
   std::string title;
   std::vector< int > values;
};

[d-frey]

The following code should now work using the latest version:

// Copyright (c) 2020 Daniel Frey and Dr. Colin Hirsch
// Please see LICENSE for license or visit https://github.com/taocpp/taopq/

#include "../macros.hpp"

#include <tao/json.hpp>
#include <tao/pq.hpp>

#include <iostream>

namespace tao::json
{
   std::string to_taopq_param( const value& v )
   {
      return to_string( v );
   }

}  // namespace tao::json

namespace tao::pq
{
   template<>
   struct result_traits< json::value >
   {
      [[nodiscard]] static json::value from( const char* value )
      {
         return json::from_string( value );
      }
   };

}  // namespace tao::pq

void run()
{
   // open a connection
   const auto conn = tao::pq::connection::create( "dbname=template1" );

   // execute statements directly
   conn->execute( "DROP TABLE IF EXISTS tao_json" );
   conn->execute( "CREATE TABLE tao_json ( id SERIAL PRIMARY KEY, content JSONB )" );

   // preparing a statement is optional, but often recommended
   conn->prepare( "insert", "INSERT INTO tao_json ( content ) VALUES ( $1 )" );

   tao::json::value v = { { "foo", tao::json::value::array( { "bar", 42, true } ) } };

   const auto res = conn->execute( "insert", v );
   TEST_ASSERT( res.rows_affected() == 1 );

   conn->execute( "insert", tao::json::value( 42 ) );
   conn->execute( "insert", tao::json::value( true ) );
   conn->execute( "insert", tao::json::value( "Hello, world!" ) );

   for( const auto& row : conn->execute( "SELECT * FROM tao_json" ) ) {
      // access fields by index or (less efficiently) by name
      std::cout << row[ 0 ].as< int >() << ": " << row[ 1 ].as< tao::json::value >() << std::endl;
   }
}

int main()
{
   try {
      run();
   }
   catch( const std::exception& e ) {
      std::cerr << "exception: " << e.what() << std::endl;
      throw;
   }
   catch( ... ) {
      std::cerr << "unknown exception" << std::endl;
      throw;
   }
}

Binding JSON values directly to structs should be explained in the JSON library's docs/examples. @ColinH might be able to explain that part better than me :)