Add ability to serialize just the keys or just the values. This would be very useful when both json and csv are needed.

[cfeied]

Add ability to serialize just the keys or just the values. This would be very useful when both json and csv are needed.

[cfeied]

I was able to obtain primitive CSV_Keys and CSV_Values from an ArduinoJson document with the following mods to JsonSerializer.hpp:

I added the following variable to the namespace:

int outFmt = 0;

I then renamed visitObject() to visitObjectForJson() and added branching logic in visitObject as follows:

  size_t visitObject(const CollectionData& object) {
      if (outFmt == 1)
          return visitObjectForCsvKeys(object);
      else if (outFmt == 2)
          return visitObjectForCsvValues(object);
      else
          return visitObjectForJson(object);
  }

  size_t visitObjectForJson(const CollectionData& object) {
      {
          write('{');

          VariantSlot* slot = object.head();

          while (slot != 0) {
              _formatter.writeString(slot->key());
              write(':');
              slot->data()->accept(*this);

              slot = slot->next();
              if (slot == 0)
                  break;

              write(',');
          }

          write('}');

          return bytesWritten();
      }
  }


  size_t visitObjectForCsvKeys(const CollectionData& object) {
      VariantSlot* slot = object.head();
      while (slot != 0) {
          _formatter.writeString(slot->key());

          slot = slot->next();
          if (slot == 0)
              break;

          write(',');
      }
      return bytesWritten();
  }

  size_t visitObjectForCsvValues(const CollectionData& object) {
      VariantSlot* slot = object.head();
      while (slot != 0) {
          slot->data()->accept(*this);

          slot = slot->next();
          if (slot == 0)
              break;

          write(',');
      }
      return bytesWritten();
  }

This seems to do exactly what I wanted (for the kind of data and structures where it could make sense), as shown by the following example:

#include <ArduinoJson.h>
#define OUTPUT_PORT Serial

void setup() {
    OUTPUT_PORT.begin(9600);
  while (!OUTPUT_PORT) continue;

  StaticJsonDocument<200> doc;
  char json[] = "{\"SensorType\":\"GPS\",\"Timestamp\":1351824120,\"Latitude\":48.756080,\"Longitude\":2.302038}";
  DeserializationError error = deserializeJson(doc, json);

  if (error) {
       OUTPUT_PORT.print(F("deserializeJson() failed: "));
       OUTPUT_PORT.println(error.f_str());
       return;
  }

  OUTPUT_PORT.print("\n\n--------------- \nSerializeJson with CSV option \n---------------\n");

  OUTPUT_PORT.print("\n\n-----\nARDUINOJSON_NAMESPACE::outFmt == 0 \nJSON string:\n\n");
  ARDUINOJSON_NAMESPACE::outFmt = 0;
  serializeJson(doc, OUTPUT_PORT);

  OUTPUT_PORT.print("\n\n-----\nARDUINOJSON_NAMESPACE::outFmt == 1 \nCSV header row:\n\n");
  ARDUINOJSON_NAMESPACE::outFmt = 1;
  serializeJson(doc, OUTPUT_PORT);

  OUTPUT_PORT.print("\n\n-----\nARDUINOJSON_NAMESPACE::outFmt == 2 \nCSV data row:\n\n");
  ARDUINOJSON_NAMESPACE::outFmt = 2;
  serializeJson(doc, OUTPUT_PORT);
  OUTPUT_PORT.print("\n\n----------\n\n");

}

void loop() 
{
  // nop
}

Producing the following output:

--------------- 
SerializeJson with CSV option 
---------------


-----
ARDUINOJSON_NAMESPACE::outFmt == 0 
JSON string:

{"SensorType":"GPS","Timestamp":1351824120,"Latitude":48.75608,"Longitude":2.302038}

-----
ARDUINOJSON_NAMESPACE::outFmt == 1 
CSV header row:

"SensorType","Timestamp","Latitude","Longitude"

-----
ARDUINOJSON_NAMESPACE::outFmt == 2 
CSV data row:

"GPS",1351824120,48.75608,2.302038

----------

I'm not submitting a pull request because I know you curate your code very meticulously -- there are better ways to achieve this, obviously, and probably plenty of variant cases to think about. I simply put it out here as food for thought.

Thanks!

Craig

[bblanchon]

Hi Craig,

A function like kv.value.serialize() would make the kv pair iteration much more useful.

This function exists; it's serializeJson().

size_t n = serializeJson(kv.value(), writePtr);

Then, you can use the return value to advance the writing pointer (ensure you don't overflow).

Best regards,
Benoit