CODEWITHSUNDEEP
c#linq
Mikey Hogarth
Mikey Hogarth

Reputation: 4702

Linq code to select one item

I find myself writing a lot of code like this to select one item that matches 

var item = (from x in Items where x.Id == 123 select x).First();

Is there a cleaner way of doing it or is this as concise as I'm going to get?

EDIT: Should have said "Cleaner way using linq syntax". I was already aware of the lambda syntax and it's starting to look like this is actually the only way. I did get some useful info though, so thanks to everyone who replied.

Upvotes: 117

Views: 244824

Answers (8)

prajun7
prajun7

Reputation: 307

If you don't have the specific Id for that table and if you need to match multiple conditions to get the unique value, we can do something like this,

var item = Items.
      .Where(x => x.Name== "Name you are looking for")
      .Where(x => x.Status == 1)
      .FirstOrDefault();

This will return the first element from the Items if that condition matches. If you are sure that the Items consist of a unique element we can use FirstOrDefault() as it will be faster.

We can also use SingleOrDefault() instead or FirstOrDefault() but it will keep on looking for the second identical element before returning the value. This might make some delay if we are querying a big database table. If we are sure that the list is unique it is better to use FirstOrDefault.

Upvotes: 0

j.rmz87
j.rmz87

Reputation: 793

I'll tell you what worked for me:

int id = int.Parse(insertItem.OwnerTableView.DataKeyValues[insertItem.ItemIndex]["id_usuario"].ToString());

var query = user.First(x => x.id_usuario == id);
tbUsername.Text = query.username;
tbEmail.Text = query.email;
tbPassword.Text = query.password;

My id is the row I want to query, in this case I got it from a radGrid, then I used it to query, but this query returns a row, then you can assign the values you got from the query to textbox, or anything, I had to assign those to textbox.

Upvotes: 2

Amal
Amal

Reputation: 461

Just to make someone's life easier, the linq query with lambda expression 

(from x in Items where x.Id == 123 select x).FirstOrDefault();

does result in an SQL query with a select top (1) in it.

Upvotes: 15

James Michael Hare
James Michael Hare

Reputation: 38397

Depends how much you like the linq query syntax, you can use the extension methods directly like:

var item = Items.First(i => i.Id == 123);

And if you don't want to throw an error if the list is empty, use FirstOrDefault which returns the default value for the element type (null for reference types):

var item = Items.FirstOrDefault(i => i.Id == 123);

if (item != null)
{
    // found it
}

Single() and SingleOrDefault() can also be used, but if you are reading from a database or something that already guarantees uniqueness I wouldn't bother as it has to scan the list to see if there's any duplicates and throws. First() and FirstOrDefault() stop on the first match, so they are more efficient.

Of the First() and Single() family, here's where they throw:

  • First() - throws if empty/not found, does not throw if duplicate
  • FirstOrDefault() - returns default if empty/not found, does not throw if duplicate
  • Single() - throws if empty/not found, throws if duplicate exists
  • SingleOrDefault() - returns default if empty/not found, throws if duplicate exists

Upvotes: 202

Chris Hannon
Chris Hannon

Reputation: 4134

That can better be condensed down to this.

var item = Items.First(x => x.Id == 123);

Your query is currently collecting all results (and there may be more than one) within the enumerable and then taking the first one from that set, doing more work than necessary.

Single/SingleOrDefault are worthwhile, but only if you want to iterate through the entire collection and verify that the match is unique in addition to selecting that match. First/FirstOrDefault will just take the first match and leave, regardless of how many duplicates actually exist.

Upvotes: 9

stuartd
stuartd

Reputation: 73253

FirstOrDefault or SingleOrDefault might be useful, depending on your scenario, and whether you want to handle there being zero or more than one matches:

FirstOrDefault: Returns the first element of a sequence, or a default value if no element is found.

SingleOrDefault: Returns the only element of a sequence, or a default value if the sequence is empty; this method throws an exception if there is more than one element in the sequence

I don't know how this works in a linq 'from' query but in lambda syntax it looks like this:

var item1 = Items.FirstOrDefault(x => x.Id == 123);
var item2 = Items.SingleOrDefault(x => x.Id == 123);

Upvotes: 21

wageoghe
wageoghe

Reputation: 27608

You could use the extension method syntax:

var item = Items.Select(x => x.Id == 123).FirstOrDefault();

Other than that, I'm not sure how much more concise you can get, without maybe writing your own specialized "First" and "FirstOrDefault" extension methods.

Upvotes: 4

James Hill
James Hill

Reputation: 61812

These are the preferred methods:

var item = Items.SingleOrDefault(x => x.Id == 123);

Or

var item = Items.Single(x => x.Id == 123);

Upvotes: 14

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