Parsing nested JSON arrays of JSON objects

Development
1

I have the following JSON object that has been read from a url stream:

**{“chatId”:“a74G5k329”,“initialMessage”:{“explanation”:“I chose the chords A, E, D, and A for a standard rock progression. These chords are commonly used in rock music and create a powerful and energetic sound. The progression follows a I-IV-V-I pattern, which is a classic choice for rock music. The key of A Major provides a good balance between brightness and richness. Enjoy rocking out with these chords!”,“midiDataUri”:“data:audio/midi;base64,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”,“chords”:[{“name”:“A”,“romanNumeral”:“I”},{“name”:“E”,“romanNumeral”:“V”},{“name”:“D”,“romanNumeral”:“IV”},{“name”:“A”,“romanNumeral”:“I”},{“name”:“A”,“romanNumeral”:“I”},{“name”:“E”,“romanNumeral”:“V”},{“name”:“D”,“romanNumeral”:“IV”},{“name”:“A”,“romanNumeral”:“I”}],“bpm”:120,“key”:“A Major”,“durationInSeconds”:16}}

Here is the code I’m using to parse the object:

const juce::String stringResponse = stream->readEntireStreamAsString();
juce::String decoded = “False”;

        int arsize;
        
        if( juce::JSON::parse(stringResponse, parsedResponse).wasOk() ) {
            juce::String midiData = parsedResponse["initialMessage"]["midiDataUri"];;
            midiBase64 = midiData.replace("data:audio/midi;base64,","");
            if(juce::Base64::convertFromBase64(midi, midiBase64)){
                decoded = "True";
            }
            juce::String chatExplanation = parsedResponse["initialMessage"]["explanation"];
            juce::Array chatChords = parsedResponse["initialMessage"].getProperty("chords",juce::var()).getArray();
            if (chatChords.isEmpty()){
                std::cout << "nothing here" << std::endl;}
            else{
                std::cout << "something here" + std::to_string(chatChords.size()) << std::endl;
            };

I’m a little new to working with JUCE and C++. I can see that chatChords is an array with a single element, but I was expecting it to be an array with 8 JSON objects. Can someone help me figure out what I am doing wrong?

2

Take a look at Jim’s repo to help your debugger get more visibility into the juce vars.

It should make it much easier to work with dynamic objects like var.

3

Hi Adam, This was really helpful. I now am able to see that chatChords does indeed have what I want. But when I try this code:
juce::var firstChord = chatChords.getFirst();
I get a compiler error that I don’t understand
Conversion function from ‘juce::Array<juce::var, juce::DummyCriticalSection, 0> *’ to ‘juce::var’ invokes a deleted function
I’ve tried every juce:: type I can think of and I get the same error. Any idea what’s going on?

4

Is the var holding a dynamic object?

https://docs.juce.com/master/classvar.html#a60a6775a9911e0047b1ac84322eac07a

Don’t know much about it but it looks JSON related…

5

When you quote a compiler error, please mark in your code, where the error occurred.

I am assuming that the deleted function is a copy constructor or assignment operator.

Note: getArray() returns a pointer, because it is not necessarily an array. I would use this check:

if (!parsedResponse.isDynamicObject())
{
    DBG ("not an object");
    return;
}
auto* object = parsedResponse.getDynamicOpject();
// ...
if (object->hasProeprty ("initialMessage"))
{
    auto& initialMessage = object->getProperty ("initialMessage");
    if (auto* chatChords = initialMessage->getProperty("chords", juce::var()).getArray())
    {
        for (auto& item : *chatChords)
        {
            if (auto* chord = item.getDynamicObject())
            {
                DBG (chord->getProperty ("name").toString() << " (" << chord->getProperty ("romanNumeral").toString() << ")");
           }
        }
    }
}

And so on. Hope that helps

1 Like
6

Hey Daniel, you are the bomb! Thanks so much for this. I’m going to look up how deleted functions happen so I won’t make the same mistake in the future.

7

For those pointery classes where you have to do a nullptr check at every line, I like to make a little class/set of functions to raise exceptions/return Results when things go wrong.

For example, if you wrap a var tree in your own class, you could override the [ ] operator to perform a getProperty() and do the nullptr/void var check. You could also override the > to do the getDynamicObject() and check for nullptr.

Do bear in mind the operator precedence if you use this, though.