I understand that the C# keyword var implies the type at compile time and therefore requires the declaration and assignment in the same place, making the following construct illegal:
var something;
if (condition)
{
something=1;
}
else
{
something = 0;
}
Even though the C# compiler could principally determine that all assignments in the current scope result in the same type, it (presently) does not and therefore generates a compile time error.
In using var with LINQ, I sometimes want to initialize my result variable slightly differently depending on program conditions. The approach I have found is to use the ?: operator, as in:
var participants = (email == null ?
(from part in db.Participant
where part.SequenceNumber == seqNr
select part)
:
(from part in db.Participant
where part.EmailAddress == email
select part));
That works well enough if I just have two possible assignments, but quickly becomes unwieldy if there are multiple possible assignments.
Is there a more elegant approach to this?
You could use .Where(...)
rather than query syntax:
var participants = email == null
? db.Participant.Where(p => p.SequenceNumber == seqNr)
: db.Participant.Where(p => p.EmailAddress == email);
but personally I simply wouldn't use var
here - it doesn't scale beyond 2, but this is a classic "search" pattern. I might use:
IQueryable<Part> query = db.Participant;
if(email != null) query = query.Where(p => p.EmailAddress == email);
if(seqNr != null) query = query.Where(p => p.SequenceNumber == seqNr);
...
// consume query
This allows multiple conditions to be composed (in this case "AND") for a more specific query. You can also do "OR" but it is slightly more complex (unless you use Concat
/Union
, which is messy).
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