Question

Suppose In SQL I am trying to run this query

Select * from MyTable where SomeCondition=true

I am currently using this lambda expression for the above query

using(var db=new DataClasses1DataContext())
{
var result=db.MyTable.Where(myTable=>myTable.SomeCondition.Equals(true)).SingleOrDefault();
}

Is this the correct way or should I do something like this

using(var db=new DataClasses1DataContext())
    {
    var result=db.MyTable.Where(myTable=>myTable.SomeCondition.Equals(true)).Select(myTable=>myTable).SingleOrDefault();
    }

Can anyone suggest me a correct way to do such type of queries in Lambda?

Any suggestions are welcome.

Answer 1

Are you asking if this part is necessary?

.Select(myTable=>myTable)

The answer is no. It turns a list of items into a list of the same items. The lambda:

x => x

Is the “identity function”, returning exactly what it is passed.

NB

Some other answers are advising FirstOrDefault as an alternative to SingleOrDefault. If the query may return multiple records, and you have no OrderBy clause, then the database may return results in random order. So using FirstOrDefault is like saying “pick one at random”.

That may be okay if all the records are “good enough” (in some sense). If not, you should add an OrderBy clause so that the first record is the “best” record. Or perhaps you want to perform the action on every record that matches your condition, in which case use neither FirstOrDefault nor SingleOrDefault`. Just loop through the results.

Finally (based on comments below) if you just want to know if there is a record that matches, but you don’t want to examine its contents, use Any.