Cannot read XSD attribute with QXMLStreamReader

jepessen

I need to parse the following XSD:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
  <xs:element name = "elementName">
    <xs:simpleType>
      <xs:restriction base = "xs:string">
      </xs:restriction>
    </xs:simpleType>
  </xs:element>
</xs:schema>

During the parsing I arrive to the restriction element. This is the code (rearranged) for parsing this element, that uses QXMLStreamReader

void String::getFromBase() const {
  QXMLStreamReader m_node; // in true code it's a class member already initialized
  m_node.readNextStartElement();
  auto name = stripNamespace(m_node.name().toString()); // convert xs:restriction to restriction
  if (name != restriction) {
    throw Exception("Restriction is not found when reading string data");
  }
  bool hasBase{false};
  auto x = m_node.attributes().size(); // x is zero but it should be one
  for (const auto& it : m_node.attributes()) {
    auto attrName = stripNamespace(it.name().toString());
    if (attrName == "base") {
      hasBase = true;
      break;
    }
  }
  if (!hasBase) {
    throw Exception("Restriction needs 'base' attribute");
  }
  auto attribute = stripNamespace(m_node.attributes().value(BaseLabel).toString());
  if (attribute == "string") {
    int i = 0;
  }
}

When I run the code, the variable name is "restriction", so I arrive to the right position in the XML. But then when I retrieve attributes with attributes() the list is empty (in the code x is equal to zero) do I don't enter in the loop for cycling all attributes.

What I'm doing wrong and what should I do for retrieving attributes of the node?

VRonin

@jepessen said in Cannot read XSD attribute with QXMLStreamReader:

(rearranged)

I think this is the key. To be able to read the attributes m_node.isStartElement() must return true just before calling m_node.attributes(). What I suspect is happening is that in the real code you are moving the cursor beyond the StartElement before calling m_node.attributes()

jepessen

@VRonin this is almost the real code I don't call readNextStartElement or readNextElement anywhere else in the function, so I' trying to retrieve attributes when m_node.name() is "restriction".

This is the actual real code (A bit incomplete because I'm focusin on this issue):

Tree::String::Ptr String::getFromBase() const {
  auto parsedNode = make_shared<Tree::String>();
  m_node.readNextStartElement();
  auto name = stripNamespace(m_node.name().toString());
  if (name != RestrictionLabel) {
    throw Exception("Restriction is not found when reading string data");
  }
  auto x = m_node.attributes().size();
  bool hasBase{ false };
  for (const auto& it : m_node.attributes()) {
    auto attrName = stripNamespace(it.name().toString());
    if (attrName == BaseLabel) {
      hasBase = true;
      break;
    }
  }
  if (!hasBase) {
    throw Exception("Restriction needs 'base' attribute");
  }
  auto attribute = stripNamespace(m_node.attributes().value(BaseLabel).toString());
  if (attribute == StringLabel) {
    int i = 0;
  }
  return parsedNode;
}

VRonin

I'm sorry but you must be moving the cursor in some way. Try putting Q_ASSERT(m_node.isStartElement()); just before auto x = m_node.attributes().size();

This example parses the XSD you provided correctly (I also let QXmlStreamReader handle namespaces instead of having to write custom code for it):

int main()
{
    const QString xmlText(R"***(<?xml version="1.0" encoding="UTF-8"?>
    <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
      <xs:element name = "elementName">
        <xs:simpleType>
          <xs:restriction base = "xs:string">
          </xs:restriction>
        </xs:simpleType>
      </xs:element>
    </xs:schema>)***"
    );
    QXmlStreamReader reader(xmlText);
    while (!reader.atEnd()) {
        switch(reader.readNext()){
        case QXmlStreamReader::StartDocument:
            qDebug("Start of document");
            break;
        case QXmlStreamReader::EndDocument:
            qDebug("End of document");
            break;
        case QXmlStreamReader::StartElement:{
            qDebug() << "Started Element: " << reader.name();
            const auto attr = reader.attributes();
            qDebug() << "Number of Attributes: " << attr.size() << " Attributes:";
            for(auto&& att : attr)
                qDebug() << att.name() << " = " << att.value();
        }
            break;
        case QXmlStreamReader::EndElement:
            qDebug() << "Finished Element: " << reader.name();
            break;
        default:
            break;
        }
    }
    return 0;
}