CODEWITHSUNDEEP
c#xmlforeach
Immanu'el Smith
Immanu'el Smith

Reputation: 693

Getting a foreach to run once

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?

Upvotes: 9

Views: 8582

Answers (11)

Eric Lippert
Eric Lippert

Reputation: 660128

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);

Upvotes: 4

gkrogers
gkrogers

Reputation: 8356

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

Upvotes: 5

sthalik
sthalik

Reputation: 337

that should do the trick:

using System.Linq;

dateQuery.Single();

Upvotes: 1

Jhonny D. Cano -Leftware-
Jhonny D. Cano -Leftware-

Reputation: 18013

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
}

Upvotes: 5

TimothyP
TimothyP

Reputation: 21755

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.

Upvotes: 2

Pharabus
Pharabus

Reputation: 6062

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

if you are able to use LINQ

Upvotes: 2

Quartermeister
Quartermeister

Reputation: 59139

Try Enumerable.Single or Enumerable.SingleOrDefault: 

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

Upvotes: 2

Oded
Oded

Reputation: 499012

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

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

Upvotes: 2

Mark Byers
Mark Byers

Reputation: 838266

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.

Upvotes: 7

tster
tster

Reputation: 18237

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

Upvotes: 20

Mark Seemann
Mark Seemann

Reputation: 233150

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

Upvotes: 8

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