How to extract value from json array with QJsonDocument format - c++

Question

I'm getting a json format like this and I want to get the value of "Duration", "Id", "LoadCumulLimit" and "Notes".
QJsonDocument({"d":{"results":[{"Duration":"420.000","Id":"123456789XYZ","LoadCumulLimit":"15.000","NavWpNioshToOpNoish":{"__deferred":{"uri":"http://xxx/WorkplaceNOISHDataSet('123456789XYZ')/NavWpNioshToOpNoish"}},"Notes":"123456789XYZ","__metadata":{"id":"xxx/WorkplaceNOISHDataSet('123456789XYZ')","type":"xxx.WorkplaceNOISHData","uri":"xxx/WorkplaceNOISHDataSet('123456789XYZ')"}}]}})
I tried to do this but it doesn't work and it return empty with array
`
QJsonDocument document = QJsonDocument::fromJson(content.toUtf8());
QJsonArray documentArray = document.array();
QStringList wordList;
for (const QJsonValue &i : documentArray)
{
//qInfo() << i.toString() << endl;
wordList << i.toString();
}
Could you guys give me a help or any suggest?

Answer 1

You could convert the QJsonDocument to a QVariant. Then you can use QVariantMap or QVariantList to walk the document and use the appropriate toString() or toDouble() to retrieve the values.
The following is hard-coded to your JSON there are only minimal validation checks included. (i.e. it is a disclaimer that the code is presented for educational purposes only and made not be production ready).
bool parse()
{
QString json = "{\"d\":{\"results\":[{\"Duration\":\"420.000\",\"Id\":\"123456789XYZ\",\"LoadCumulLimit\":\"15.000\",\"NavWpNioshToOpNoish\":{\"__deferred\":{\"uri\":\"http://xxx/WorkplaceNOISHDataSet('123456789XYZ')/NavWpNioshToOpNoish\"}},\"Notes\":\"123456789XYZ\",\"__metadata\":{\"id\":\"xxx/WorkplaceNOISHDataSet('123456789XYZ')\",\"type\":\"xxx.WorkplaceNOISHData\",\"uri\":\"xxx/WorkplaceNOISHDataSet('123456789XYZ')\"}}]}}";
QJsonDocument document = QJsonDocument::fromJson(json.toUtf8());
if (document.isEmpty() || document.isNull()) return false;
QVariantMap root = document.toVariant().toMap();
if (root.isEmpty()) return false;
QVariantMap d = root["d"].toMap();
if (d.isEmpty()) return false;
QVariantList results = d["results"].toList();
if (results.isEmpty()) return false;
foreach (QVariant varResult, results)
{
QVariantMap result = varResult.toMap();
if (result.isEmpty()) return false;
bool ok = true;
double duration = result["Duration"].toDouble(&ok);
if (!ok) return false;
QString id = result["Id"].toString();
if (id.isEmpty() || id.isNull()) return false;
double loadCumulLimit = result["LoadCumulLimit"].toDouble(&ok);
if (!ok) return false;
QString notes = result["Notes"].toString();
if (!notes.isEmpty() || notes.isNull()) return false;
qDebug() << id << duration << loadCumulLimit << notes; // "123456789XYZ" 420 15 "123456789XYZ"
}
return true;
}
Alternatively, you can just use QJsonDocument, QJsonValue and QJsonArray to walk the document and use the corresponding toString() and toDouble() to retrieve the values. Again, there are minimal validation checks included:
bool parse2()
{
QString json = "{\"d\":{\"results\":[{\"Duration\":\"420.000\",\"Id\":\"123456789XYZ\",\"LoadCumulLimit\":\"15.000\",\"NavWpNioshToOpNoish\":{\"__deferred\":{\"uri\":\"http://xxx/WorkplaceNOISHDataSet('123456789XYZ')/NavWpNioshToOpNoish\"}},\"Notes\":\"123456789XYZ\",\"__metadata\":{\"id\":\"xxx/WorkplaceNOISHDataSet('123456789XYZ')\",\"type\":\"xxx.WorkplaceNOISHData\",\"uri\":\"xxx/WorkplaceNOISHDataSet('123456789XYZ')\"}}]}}";
QJsonDocument document = QJsonDocument::fromJson(json.toUtf8());
if (document.isEmpty() || document.isNull()) return false;
QJsonValue d = document["d"];
if (d.isNull() || d.isUndefined()) return false;
QJsonArray results = d["results"].toArray();
if (results.isEmpty()) return false;
foreach (QJsonValue result, results)
{
double duration = result["Duration"].toDouble();
QString id = result["Id"].toString();
if (id.isEmpty() || id.isNull()) return false;
double loadCumulLimit = result["LoadCumulLimit"].toDouble();
QString notes = result["Notes"].toString();
if (!notes.isEmpty() || notes.isNull()) return false;
qDebug() << id << duration << loadCumulLimit << notes; // "123456789XYZ" 420 15 "123456789XYZ"
}
return true;
}

Answer 2

You have:
object d {
object results {
[ { several objects to be extracted} ]
}
}
To extract a value of an object by given a key, call operator[](key) on QJsonValue.
When you have an array, to extract its first item call operator[](0) on this array. When you have found an object at desired key, you can convert its value to the value of specified type by toString/toInt/toDouble etc. methods of QJsonValue.
Short version:
QJsonValue item0 = document["d"]["results"].toArray()[0];
QStringList wordList;
wordList << item0["Duration"].toString() << item0["Id"].toString() << item0["LoadCumulLimit"].toString() << item0["Notes"].toString();
the longer version:
QJsonValue dObj = document["d"];
QJsonValue resultsObj = dObj["results"];
QJsonArray resultsArray = resultsObj.toArray();
QJsonValue item0 = resultsArray[0];
QStringList wordList;
wordList << item0["Duration"].toString() << item0["Id"].toString() << item0["LoadCumulLimit"].toString() << item0["Notes"].toString();