JSon Parsing

jemazter

Hello.

I developing a application that makes a request to an server and i get the following response (https://octopart.com/api/v3/parts/match?apikey=EXAMPLE_KEY&queries=[{"mpn":"SN74S74N"}]&pretty_print=true&include[]=specs&include[]=specs). I need to access the variable "results">"specs">"case_package">"value". This is my code:

void MainWindow::octopartData(QByteArray data)
{
    QString dataString;
    dataString = data;
    // ui->textBrowser->append(data); //DEBUG PURPOSES
    QJsonDocument temp = QJsonDocument::fromJson(data);
    QJsonObject jObject = temp.object();
    QVariantMap mainMap = jObject.toVariantMap();
    QVariantMap results = mainMap["results"].toMap();
    QVariantMap specs = results["specs"].toMap();
    QVariantMap case_package = specs["case_package"].toMap();
    qDebug()<<case_package["value"];
}

But is not working, debug is showing only QVariant(Invalid). I would like to get some advice to solve this problem.

Thanks in advance.

VRonin

use toObject instead of toVariantMap

mrjj

Hi
Why you need to convert to
Object.toVariantMap();

If you take

  qDebug() << jObject["message"] <<  jObject["__class__"];

Its not the values?

See small sample here
https://forum.qt.io/topic/74715/work-with-json-format/3

Its parsing
"[ { "Name" : "Bob", "Phonenumber" : 123 },
{ "Name" : "Alice", "Phonenumber" : 321 } ]"

so almost the same :)

jemazter

@mrjj said in JSon Parsing:

Hi
Why you need to convert to
Object.toVariantMap();

If you take
  qDebug() << jObject["message"] <<  jObject["__class__"];
Its not the values?

See small sample here
https://forum.qt.io/topic/74715/work-with-json-format/3

Its parsing
"[ { "Name" : "Bob", "Phonenumber" : 123 },
{ "Name" : "Alice", "Phonenumber" : 321 } ]"

so almost the same :)

Hi.

I'm converting it to VariantMap because i was following this http://blog.linux4us.org/2013/09/05/parse-json-with-qjson-in-qt5/. The data i have is like the following: https://paste2.org/yIBBGm8p

I think the difference between my data and the example you posted is that in my data the value i want to read ("value") is "inside" "case_package", that is inside "specs" that is inside "results".

VRonin

Edit2

I corrected the code. You did not realise some of the values were arrays and that there was an "items" object in-between.

You can use tools like http://jsonviewer.stack.hu/ to have a clearer view of what you are looking at

void MainWindow::octopartData(QByteArray data)
{
    const QJsonDocument temp = QJsonDocument::fromJson(data);
    const QJsonObject jObject = temp.object();
    const QJsonArray results = jObject["results"].toArray();

    for(const QJsonValue& res : results){
        const QJsonObject result= res.toObject();
        const QJsonArray items = result["items"].toArray();
        for(const QJsonValue& ite : items){
            const QJsonObject item= ite.toObject();
            const QJsonObject specs = item["specs"].toObject();
            const QJsonObject case_package = specs["case_package"].toObject();
            const QJsonArray value = case_package["value"].toArray();
            for(auto& val : value){
                qDebug() << val;
            }
        }
    }
}

jemazter

@VRonin said in JSon Parsing:

Edit2

I corrected the code. You did not realise some of the values were arrays and that there was an "items" object in-between.

You can use tools like http://jsonviewer.stack.hu/ to have a clearer view of what you are looking at

void MainWindow::octopartData(QByteArray data)
{
    const QJsonDocument temp = QJsonDocument::fromJson(data);
    const QJsonObject jObject = temp.object();
    const QJsonArray results = jObject["results"].toArray();

    for(const QJsonValue& res : results){
        const QJsonObject result= res.toObject();
        const QJsonArray items = result["items"].toArray();
        for(const QJsonValue& ite : items){
            const QJsonObject item= ite.toObject();
            const QJsonObject specs = item["specs"].toObject();
            const QJsonObject case_package = specs["case_package"].toObject();
            const QJsonArray value = case_package["value"].toArray();
            for(auto& val : value){
                qDebug() << val;
            }
        }
    }
}

Hello.

Thanks, it's working now. Sorry for the newbie question, but what the 3 '"fors" are doing exactly?

And just one more question, if inside "items" i have "0" and "1", how can i select one of these itens?

VRonin

the answers are related:

but what the 3 '"fors" are doing exactly?

they iterate over every item of the array

if inside "items" i have "0" and "1", how can i select one of these itens?

instead of iterating over all of them (with the for) you can use at() to select a specific one, for example: const QJsonObject item= items.at(0).toObject();

jemazter

Thanks a lot, @VRonin.

jemazter

Sorry, for "reviving" the topic, but i have one more doubt.

I'm trying to acces the property "mpn" from "itens" using the following code:

void MainWindow::octopartData(QByteArray data)
{
    const QJsonDocument temp = QJsonDocument::fromJson(data);
    const QJsonObject jObject = temp.object();
    const QJsonArray results = jObject["results"].toArray();
    for(const QJsonValue& res : results)
{
        const QJsonObject result= res.toObject();
        const QJsonArray items = result["items"].toArray();
        const QJsonObject item = items.at(0).toObject();
        const QJsonArray mpn = item["mpn"].toArray();
        qDebug() << mpn;
    }
}

But i only get an empty array. Did i did something wrong when accessing the data?

mrjj

Hi
"mpn": "SN74S74N",
Do not look like array to me.
Looks like a value.
http://doc.qt.io/qt-5/qjsonvalue.html#details
"The type of the value can be queried with type() or accessors like isBool(), isString(), and so on. "

so try the type() and see what you got :)

jemazter

@mrjj said in JSon Parsing:

Hi
"mpn": "SN74S74N",
Do not look like array to me.
Looks like a value.
http://doc.qt.io/qt-5/qjsonvalue.html#details
"The type of the value can be queried with type() or accessors like isBool(), isString(), and so on. "

so try the type() and see what you got :)

It was a string after all. Now my code is working as bellow:

void MainWindow::octopartData(QByteArray data)
{
    const QJsonDocument temp = QJsonDocument::fromJson(data);
    const QJsonObject jObject = temp.object();
    const QJsonArray results = jObject["results"].toArray();
    for(const QJsonValue& res : results)
{
        const QJsonObject result= res.toObject();
        const QJsonArray items = result["items"].toArray();
        const QJsonObject item = items.at(0).toObject();
        const QString mpn = item["mpn"].toString();
        qDebug() << mpn;
    }
}

Thanks a lot for the help.

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Edit2

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