Updating XML nodes from an object list in C#

Question

I have an XML file with this structure:

<inventory>
<product>
    <recordNumber>1</recordNumber>
    <name>Dustbin</name>
    <stock>190</stock>
    <price>33</price>
</product>
<product>
    <recordNumber>2</recordNumber>
    <name>Broom</name>
    <stock>200</stock>
    <price>76</price>
</product>

</inventory>

I have a program which takes in these values and creates a List of 'Item' objects called 'stockArray'. each item has an int-Id(from recordNumber) and an int-count(from stock).

The program updates the "stock" value accordingly and what I am looking to do is then update the XML file to have the new 'stock' value.

I am very new to C# and XML, so this is the path I have been going down:

XDocument doc = XDocument.Load(xml);

var list = doc.Element("inventory").Elements("product");

foreach (var node in list)
{
    foreach (Item item in stockArray)
    {
        if (node.Element("recordNumber").Value == Convert.ToString(item.Id))
            node.SetElementValue("count", Convert.ToString(item.count));
    }
}

But so far this seems way off course. I can find a lot of information about adding new nodes to an XML but iterating through the stockArray item list and updating the XML seems to be a different process.

Any advice would be greatly appreciated.

Probably that it is very slow if the file is large. YOu have to iterate over everything. Yuck. I'd look into using linq — Ray Suelzer
– Ray Suelzer, Commented Aug 25, 2014 at 7:00
It does not seem to be modifying the XML document at all. When I reload the program the original stock number is there. Thanks — Daviepark
– Daviepark, Commented Aug 25, 2014 at 7:00
you don't have <count> element, did you mean stock : node.SetElementValue("stock", Convert.ToString(item.count)); ? — har07
– har07, Commented Aug 25, 2014 at 7:07

har07 · Accepted Answer · 2014-08-25 07:21:13Z

2

Your XML doesn't have <count> element. If you meant to update <stock> element value, the first parameter of SetElementValue() should be "stock" :

if (node.Element("recordNumber").Value == Convert.ToString(item.Id))
    node.SetElementValue("stock", Convert.ToString(item.count));

One possible way using LINQ join to create anonymous type that pair <product> element with the corresponding item from stockArray :

var list = from product in doc.Element("inventory").Elements("product")
           join item in stockArray on (int)product.Element("recordNumber") equals item.id
           select new {product = product, item = item};
foreach (var joinedProduct in list)
{
    joinedProduct.product.SetElementValue("stock", joinedProduct.item.count);
}

edited Aug 25, 2014 at 7:21

answered Aug 25, 2014 at 7:09

har07

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Ray Suelzer · Accepted Answer · 2014-08-25 07:09:17Z

0

Try this, but you will want to do some error handling for null values.

var doc = XDocument.Load(xml);
var list = doc.Element("inventory").Elements("product");

 foreach (var item in stockArray)
   {
   var node = list.FirstOrDefault(p => p.Element("recordNumber").Value == item.ToString());
            node.Element("stock").Value = item.Count.ToString();
   }

Edit: fixing the code!

answered Aug 25, 2014 at 7:09

Ray Suelzer

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2 Comments

Tim Over a year ago

p => (string)p.Element("recordNumber") == item.ToString() will handle the case of an element being null without having to check if it's null or not (or if the element is missing).

Ray Suelzer Over a year ago

That is rad! Learn something new every day.

Seminda · Accepted Answer · 2014-08-25 07:24:04Z

You can use XmlSerializer to do this. Only thing is you have to write your xml structure as classes. see the code sample.

class Program
{
    static void Main(string[] args)
    {
        // Create a new file stream for reading the XML file
        FileStream ReadFileStream = new FileStream(@"C:\files\data.xml", FileMode.Open, FileAccess.ReadWrite, FileShare.ReadWrite);

        // Load the object saved above by using the Deserialize function
        Inventory LoadedObj = (Inventory)SerializerObj.Deserialize(ReadFileStream);

        // Cleanup
        ReadFileStream.Close();

        foreach (var node in LoadedObj.Products)
        {
             // node.Stock = 0;
            //Do what ever changes to stock
        }

        XmlSerializer SerializerObj = new XmlSerializer(typeof(Inventory));
        //// Create a new file stream to write the serialized object to a file
        TextWriter WriteFileStream = new StreamWriter(@"C:\files\data.xml");
        SerializerObj.Serialize(WriteFileStream, TestObj);
        //// Cleanup
        WriteFileStream.Close();


    }
}


[System.SerializableAttribute()]
[System.Xml.Serialization.XmlRoot("inventory")]
public class Inventory
{
    [System.Xml.Serialization.XmlElement("product")]
    public List<Product> Products { get; set; }

}

[System.SerializableAttribute()]

   public class Product
{
    [System.Xml.Serialization.XmlElementAttribute("recordNumber")]
    public string RecordNumber { get; set; }
    [System.Xml.Serialization.XmlElementAttribute("name")]
    public string Name { get; set; }
    [System.Xml.Serialization.XmlElementAttribute("stock")]
    public int Stock { get; set; }
    [System.Xml.Serialization.XmlElementAttribute("price")]
    public int Price { get; set; }
}

Yuval Itzchakov · Accepted Answer · 2014-08-25 07:45:44Z

0

You are editing the count element instead of stock element.

And to improve performance (here the complexity is O(n^2)). You can create a dictionary from the stockArray.

Creating the dictionary has a complexity of O(n). And getting a value in the dictionary has a complexity of O(1).

So, the complexity of the program with the dictionary is O(n).

I would also suggest you to use the explicit cast to convert the value of the XElement to int.

XDocument doc = XDocument.Load(xml);

var list = doc.Element("inventory").Elements("product");
var stockDictionary = stockArray.ToDictionary(item => item.Id, item => item.Count);

foreach (var node in list)
{
    int newCount;
    if (if(stockDictionary.TryGetValue((int)node.Element("recordNumber"), out newCount)
        node.SetElementValue("stock", newCount);
}

edited Aug 25, 2014 at 7:45

Yuval Itzchakov

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answered Aug 25, 2014 at 7:13

Cédric Bignon

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2 Comments

Ray Suelzer Over a year ago

Does the compiler automatically generate a recursive loop from LINQ Statements. For example if he grabbed the node using:list.FirstOrDefault(p => p.Element("recordNumber").Value ....

Cédric Bignon Over a year ago

Yes it does (in a way). This is why the complexity of using list.FirstOrDefault(...) is O(n). So with this, the complexity of the program is still O(n^2). There is a way to do it in pure LINQ without dictionaries and having a O(n) complexity for the program (using the .Join(...) method) but it unecessarily complexify the code.

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