Question

I am new to LINQ. I need to return the id with the correct price information for today’s date for each MPrice.

Here is an example of the XML:

<Pricing>
<MPrice>
    <Id>0079</Id>
      <Price>
        <Price>31.25</Price>
        <StartDt>2009-8-01</StartDt>
        <EndDt>2009-08-26</EndDt>
      </Price>
      <Price>
        <ListPrice>131.25</ListPrice>
        <StartDt>2009-08-26</StartDt>
        <EndDt>9999-12-31</EndDt>
       </Price>
   </MPrice>
   <MPrice>
    <Id>0081</Id>
      <Price>
        <Price>131.25</Price>
        <StartDt>2009-8-01</StartDt>
        <EndDt>2009-08-26</EndDt>
      </Price>
      <Price>
        <ListPrice>231.25</ListPrice>
        <StartDt>2009-08-26</StartDt>
        <EndDt>9999-12-31</EndDt>
       </Price>
   </MPrice> 
</Pricing>

Answer 1

Here is one way of doing it:

using System;
using System.Linq;
using System.Xml.Linq;

class Program
{
    static void Main()
    {
        String xml = @"<Pricing>
            <MPrice>
                <Id>0079</Id>
                <Price>
                <Price>31.25</Price>
                <StartDt>2009-8-01</StartDt>
                <EndDt>2009-08-26</EndDt>
                </Price>
                <Price>
                <ListPrice>131.25</ListPrice>
                <StartDt>2009-08-26</StartDt>
                <EndDt>9999-12-31</EndDt>
                </Price>
            </MPrice>
           </Pricing>";

        var priceInfo = from e in XElement.Parse(xml).Elements("MPrice").Elements("Price")
                let start = DateTime.Parse(e.Descendants("StartDt").FirstOrDefault().Value)
                let end = DateTime.Parse(e.Descendants("EndDt").FirstOrDefault().Value)
                where start < DateTime.Now && end > DateTime.Now
                select new { Id = e.Parent.Element("Id").Value, ListPrice = e.Element("ListPrice").Value };

        Console.WriteLine(priceInfo.FirstOrDefault().Id);
        Console.WriteLine(priceInfo.FirstOrDefault().ListPrice);
    }
}

Output:

0079
131.25

Please note that there needs to be much more error checking than this example provides. I would specifically add checking around the parsing of the datetime (perhaps by using a function that wraps DateTime.TryParseExact).

Edit: If you want to use an XDocument instead of an XElement you will need to make a subtle change to the query (notice the usage of the Descendants method instead of the Elements method):

var priceInfo = from e in XDocument.Parse(xml).Descendants("MPrice").Elements("Price")
        let start = DateTime.Parse(e.Descendants("StartDt").FirstOrDefault().Value)
        let end = DateTime.Parse(e.Descendants("EndDt").FirstOrDefault().Value)
        where start < DateTime.Now && end > DateTime.Now
        select new { Id = e.Parent.Element("Id").Value, ListPrice = e.Element("ListPrice").Value };

Remember that you don’t need to use an XDocument unless you are working with the XML as a true document. In most cases, the XElement type is sufficient.

Edit #2: If you want to load the XDocument from disk then use this approach:

using System;
using System.Linq;
using System.Xml.Linq;

class Program
{
    static void Main()
    {
        XDocument document = XDocument.Load(@"d:\test.xml");

        var priceInfo = from e in document.Descendants("MPrice").Elements("Price")
                let start = DateTime.Parse(e.Descendants("StartDt").FirstOrDefault().Value)
                let end = DateTime.Parse(e.Descendants("EndDt").FirstOrDefault().Value)
                where start < DateTime.Now && end > DateTime.Now
                select new { Id = e.Parent.Element("Id").Value, ListPrice = e.Element("ListPrice").Value };

        Console.WriteLine(priceInfo.FirstOrDefault().Id);
        Console.WriteLine(priceInfo.FirstOrDefault().ListPrice);
    }
}