Going crazy trying to check if a key exists! about arduinojson HOT 6 CLOSED

I managed eventually to resolve this (may or may not be "best practise") by simply doing:

const char* meter_serial_number = doc[_meterID][0]["variable1"];

from arduinojson.

Hi @IAmOrion,

Yes, this corresponds to the library's best practices.

You seemed upset in your initial message.
I'm assuming this was due to a problem in ArduinoJson's documentation or tooling.
Please let me know if there is anything I can do to improve them.

Best regards,
Benoit

from arduinojson.

Hi @IAmOrion,

Yes, this corresponds to the library's best practices.

You seemed upset in your initial message. I'm assuming this was due to a problem in ArduinoJson's documentation or tooling. Please let me know if there is anything I can do to improve them.

Best regards, Benoit

Hi @bblanchon

Not upset as such, I was frustrated at not getting it to work.

To summarise the docs https://arduinojson.org/v7/api/jsonvariant/containskey/

JsonDocument doc;
JsonVariant root = doc.to<JsonVariant>();
...
const char* error = root["error"];
if (error) {
  Serial.println(error);
  return;
}

or https://arduinojson.org/v7/api/jsonobject/containskey/

JsonDocument doc;
JsonObject root = doc.to<JsonObject>();

const char* error = root["error"];
if (error) {
  Serial.println(error);
  return;
}

did not work for me.

Specifically,

JsonObject root = doc.to<JsonObject>();
const char* error = root["error"];

eventually seemed to be not needed when I could directly access doc[]

So in my case

JsonDocument doc;
JsonObject root = doc.to<JsonObject>();

const char* error = root[_meterID][0]["variable1"];
if (error) {
  Serial.println(error);
  return;
}

Never worked. I tried variations too like:

const char* error = root[_meterID]["variable1"];
const char* error = root[_meterID][0]["variable1"][0];
const char* error = root[0][_meterID][0]["variable1"][0];

But these also never worked.

I ultimately skipped the JsonObject root = doc.to<JsonObject>(); part and just used the following

const char* meter_serial_number = doc[_meterID][0]["variable1"];

which rendered the inital part of the docs example not needed. Either that, or the example just confused me resulting in me misunderstanding

Hope that all makes sense :)

from arduinojson.

Thank you for the feedback, @IAmOrion.
Indeed people often confuse JsonDocument::to<T>() with JsonDocument::as<T>(); I shouldn't have used it here.
I updated the examples so they don't rely on JsonDocument::to<T>().
Let me know if this still needs improvement.

from arduinojson.

If I was to give some critical feedback I'd say these need fixing too... in my personal opinion they would be better suited as self contained examples so to so speak, because now you've removed the JsonObject root = doc.to<JsonObject>(); part there's no obvious link to what "root" even is here: const char* error = root["error"];

As an example - to me this is a standalone working example

Hopefully that makes sense.

Great work on this library btw, I appreciate you taking the time to see where you can improve and adapt things if needed

from arduinojson.

Thank you again for the feedback.
I updated the pages according to your suggestion.
Let me know if you find other confusing things on the site.

from arduinojson.