Appending an existing XML file with XmlWriter

问题

I\'ve used the following code to create an XML file:

XmlWriterSettings xmlWriterSettings = new XmlWriterSettings();
xmlWriterSettings.Indent = true;
xmlWriterSettings.NewLineOnAttributes = true;
using (XmlWriter xmlWriter = XmlWriter.Create(\"Test.xml\", xmlWriterSettings))
{
   xmlWriter.WriteStartDocument();
   xmlWriter.WriteStartElement(\"School\");
   xmlWriter.WriteEndElement();
   xmlWriter.WriteEndDocument();
   xmlWriter.Close();
 }

I need to insert nodes dynamically creating the following structure:

<?xml version=\"1.0\" encoding=\"utf-8\"?>
<School />
   <Student>
      <FirstName>David</FirstName>
      <LastName>Smith</LastName>
   </Student>
   ...
   <Teacher>
      <FirstName>David</FirstName>
      <LastName>Smith</LastName>
   </Teacher>
   ...
</School>

How can I do it? The values of \"FirstName\" and \"LastName\" should be read from the keyboard and the values ​​can be entered at any time, of course under existing.

回答1:

you can use Linq Xml

XDocument doc = XDocument.Load(xmlFilePath);
XElement school = doc.Element("School");
school.Add(new XElement("Student",
           new XElement("FirstName", "David"),
           new XElement("LastName", "Smith")));
doc.Save(xmlFilePath);

Edit

if you want to add Element to Existing <Student>, just add an Attribute before

school.add(new XElement("Student",
           new XAttribute("ID", "ID_Value"),
           new XElement("FirstName", "David"),
           new XElement("LastName", "Smith")));

Then you can add further Details to the Existing <Student> by search -> get -> add

XElement particularStudent = doc.Element("School").Elements("Student")
                                .Where(student => student.Attribute("ID").Value == "SearchID")
                                .FirstOrDefault();
if(particularStudent != null)
    particularStudent.Add(new XElement("<NewElementName>","<Value>");

回答2:

finally I succeeded :)

if (!File.Exists("Test.xml"))
{
   XmlWriterSettings xmlWriterSettings = new XmlWriterSettings();
   xmlWriterSettings.Indent = true;
   xmlWriterSettings.NewLineOnAttributes = true;
   using (XmlWriter xmlWriter = XmlWriter.Create("Test.xml", xmlWriterSettings))
   {
      xmlWriter.WriteStartDocument();
      xmlWriter.WriteStartElement("School");

      xmlWriter.WriteStartElement("Student");
      xmlWriter.WriteElementString("FirstName", firstName);
      xmlWriter.WriteElementString("LastName", lastName);
      xmlWriter.WriteEndElement();

      xmlWriter.WriteEndElement();
      xmlWriter.WriteEndDocument();
      xmlWriter.Flush();
      xmlWriter.Close();
   }
}
else
{
   XDocument xDocument = XDocument.Load("Test.xml");
   XElement root= xDocument.Element("School");
   IEnumerable<XElement> rows = root.Descendants("Student");
   XElement firstRow= rows.First();
   firstRow.AddBeforeSelf(
      new XElement("Student",
      new XElement("FirstName", firstName),
      new XElement("LastName", lastName)));
   xDocument.Save("Test.xml");
}

回答3:

Let me give you a suggestion. When you creating your xml file, give an unique id to your students like this:

// to store the id variable, if you create more than one student you can increase it
count = 0; 

xmlWriter.WriteStartElement("School");
xmlWriter.WriteAttributeString("ID",count.ToString());
xmlWriter.WriteEndElement();

Then when you need to add information to this student you can get ID,Firstname and Lastname and you can edit your XML file with LINQ to XML like this:

int id = Convert.ToInt32(txtStudentId.Text);
XDocument xDoc = XDocument.Load("Test.xml");
XElement student = xDoc.Descendants("Student").Where(x => (string) x.Attribute("ID") == id).FirstOrDefault();

if (student != null)
{
   string firstName = txtFirstName.Text;
   string lastName = txtLastName.Text;
   XElement first = new XElement("FirstName", firstName);
   XElement last = new XElement("LastName", lastName);
   student.Add(first);
   student.Add(last);
   xDoc.Save("Test.xml");
}

回答4:

I know you asked for XmlWriter, but I believe you can achieve this using less code with XDocument. Here is my solution:

var filePath = "path/XmlFile.xml";
var xmlDoc = XDocument.Load(filePath);
var parentElement = new XElement("Student");
var firstNameElement = new XElement("FirstName", firstNameVariable);
var lastNameElement = new XElement("LastName", lastNameVariable);

parentElement.Add(firstNameElement);
parentElement.Add(lastNameElement);

var rootElement = xmlDoc.Element("School");
rootElement?.Add(parentElement);

xmlDoc.save();

This is based on the following XML structure and will append at ... :

<School>
  <Student>
    <FirstName>John</FirstName>
    <LastName>Johnson</LastName>
  </Student>
...
</School>

Hope this helps!

回答5:

I have a suggestion for the next time:

string nameFile = "Test.xml";
bool newFile = false;


if (!File.Exists(nameFile))
{
    newFile = true;
    XmlWriterSettings xmlWriterSettings = new XmlWriterSettings();
    xmlWriterSettings.Indent = true;
    xmlWriterSettings.NewLineOnAttributes = true;

    xmlWriter.WriteStartDocument();
    xmlWriter.WriteStartElement("School");

    xmlWriter = XmlWriter.Create("Test.xml", xmlWriterSettings))
}
else
{
    doc = new XmlDocument();
    doc.Load(nameFile);

    // Create a XPathNavigator
    // You can go where you want to add
    // In this case it is just after last child of the roor
    XPathNavigator navigator = doc.CreateNavigator();     

    navigator.MoveToChild("School", "");
    xmlWriter = navigator.AppendChild();
}

// From here you can work only with xmlWriter,
// One will point on a file and the other on the stream of xmlDocument
// So you will need to save the document in the second choise

xmlWriter.WriteStartElement("Student");
xmlWriter.WriteElementString("FirstName", firstName);
xmlWriter.WriteElementString("LastName", lastName);
xmlWriter.WriteEndElement();


// End document / close or save. 
if (newFile)
    xmlWriter.WriteEndDocument();

xmlWriter.Close();

if (!newFile)
    doc.Save(nameFile);

It should work. :)

来源：https://stackoverflow.com/questions/20922835/appending-an-existing-xml-file-with-xmlwriter