Getting a foreach to run once

Question

So the question is this, I have a for each loop that I am currently using to retrieve data from a query of an XML file which then gets put into a string; like so:

foreach (var value in dateQuery)
                date = value.Element("HistoryCreation").Value;

I know for a fact (Based on the way the xml file stores values and the query being used) that there will only be one value in dateQuery.

Thus, I would like to know (for the purposes of making my program more efficient and learning how to code better), is there a better way to do this or are foreach's the only way?

Answer 1

date = dateQuery.Single().Element("HistoryCreation").Value;

Answer 2

You could use:

dateQuery.First().Element("HistoryCreation").Value

This won't fail if there is multiple items in the query. If you want it to fail if there are multiple items, then use Single

Answer 3

If you are using .NET 3.5 or newer you could use the extension method Enumerable.Single:

var value = dateQuery.Single();
date = value.Element("HistoryCreation").Value;

Then if your assumption 'there will only be one value in dateQuery' is wrong it will throw an exception.

Answer 4

Can't you simply access the first index of dateQuery?

date = dateQuery[0].Element("HistoryCreation").Value;

Answer 5

Try Enumerable.Single or Enumerable.SingleOrDefault:

 date = dateQuery.Single().Element("HistoryCreation").Value;

Answer 6

dateQuery.First().Element("HistoryCreation").Value

if you are able to use LINQ

Answer 7

You can try

var theValue = dateQuery.FirstOrDefault();
if (theValue != null)
{
   data = theValue.Element("HistoryCreation").Value;
}
else
{
       //Deal with the fact that there is no data
}

You could use .First() or .Single(), but if there is nothing in dataQuery an exception will be thrown.

Answer 8

Mark's Answer is by far the best, but I put mine for illustrating foreach loop.

foreach (var value in dateQuery) {
    date = value.Element("HistoryCreation").Value;
    break;  // break current loop
}

Answer 9

that should do the trick:

using System.Linq;

dateQuery.Single();

Answer 10

Emmanual, if you know you only need to do something once, you shouldn't use a loop.

Answer 11

Summing up:

• use First() if you want the first item and know that there is at least one (or more) items in the sequence.
• use FirstOrDefault() if the sequence can have any number of items
• use Single() if the sequence can have exactly one item
• use SingleOrDefault() if the sequence always has either zero or one item

Note that there are also versions of these which take predicates, so that you can abbreviate

var result = sequence.Where(predicate).First();

to

var result = sequence.First(predicate);