Add in JSON Array

Mikeeeeee

Hi!
There is the array in json-file. In need to add ther other element of this array. But it takes a lot of time to load whole array. How can I add one element quickly?

sneubert

Hi @Mikeeeeee,

please provide some more information. Do you use QJsonDocument or javascript JSON in qml? Can you provide a minimal example?

Mikeeeeee

Yes, I use QJsonDocument. There is only one array in json file. There is QString LastResume in my project. I would like to add LastResume in the array in json file. But json file may be is large. That's why I don't want load the whole file.

sneubert

Since JSON is a text file, you maybe faster in creating two QTextStream, one for reading your JSON file, and one for writing to a new file. You can process the input file line by line until you hit the array end character ], where you can insert your string. This is kind of change by copy. But I don´t know if this is really faster, you have to try.

Maybe someone else here has experience in modifying large files. Maybe this can be faster with memory mapping the file?

mrjj

Hi
What Qt version are you using ?
The array must be ULTRA huge for it to take time.
https://bugreports.qt.io/browse/QTBUG-44737

so i wonder if its older Qt version.

Mikeeeeee

My version 5.11.2

json file can occupy several gigabytes

jsulm

@Mikeeeeee said in Add in JSON Array:

json file can occupy several gigabytes

!
Wondering what the use case for such huge JSON file is...

Mikeeeeee

I predicted to use it for saving array. But I desided to use SQL.

mrjj

@Mikeeeeee
Using SQL is way better as a JSON file this size will consume TONS of memory with a DOM parser like QJsonDocument.

Christian Ehrlicher

QJson also has an internal memory limit which is imo below 1GB. There was a thread about this on the mailing list some months ago (during the cbor introduction iirc)

sierdzio

@Christian-Ehrlicher said in Add in JSON Array:

QJson also has an internal memory limit which is imo below 1GB. There was a thread about this on the mailing list some months ago (during the cbor introduction iirc)

That limit (128 MB) is for saving to binary JSON only, if I recall correctly.