FirstOrDefault() || Select() which is faster?

Question

In general, is one faster than the other, assuming 1 record is being returned?

Are there benefits to using one over the other?

Just as an example:

DataContext.TableBlah.FirstOrDefault(_blah => _blah.id == 1);

or

var test = (from blah in TableBlah
            where blah.id == 1
            select blah)

Answer 1

var test = (from blah in TableBlah
            where blah.id == 1
            select blah)

This can return more than 1 rows, for matching records (As against FirstOrDefault).

Performance wise, I don't think it should be any different.
It also depends on number of rows in the table? Is Id column indexed?

Answer 2

FirstOrDefault returns as soon as it finds a result, so it can be slightly faster, but not by an order of magnitude... Anyway, your second query can return more than one result, so it's not really a fair comparison. You could compare it to SingleOrDefault instead, which is like a Select, but returns just 1 result.

SingleOrDefault, like a Select, must go through the complete list, but it guarantees that you get one and only one result.

Note: If you're using Linq to SQL, than you second query can be faster, depends on your indexes...

Answer 3

This can potentially be faster.

var test = (from blah in TableBlah
        where blah.id == 1
        select blah)

It depends on which LINQ provider you're using. If you're using LINQ to Sql or Subsonic, etc, this can get translated into a direct SQL call, which will only fetch one row from the DB.

In LINQ to Objects, the two statements will be nearly identical, due to LINQs streaming of results.

Answer 4

I'm 90% certain that

var test = dc.TableBlah.FirstOrDefault(_blah => _blah.id == 1);

sets up the exact same expression tree as

var test = (from blah in dc.TableBlah
            where blah.id == 1
            select blah).FirstOrDefault();

So your second example simply lacks the benefit of getting a single record by calling FirstOrDefault(). In terms of performance, they'll be identical.

Personally, I would use SingleOrDefault() instead, since you're looking for a single item. SingleOrDefault() will throw if you receive more than one record.