How to force LINQ Sum() to return 0 while source collection is empty

.net c# entity-framework

Question

Basically when I do the following query, if no leads were matched the following query throws an exception. In that case I'd prefer to have the sum equalize 0 rather than an exception being thrown. Would this be possible in the query itself - I mean rather than storing the query and checking query.Any() ?

double earnings = db.Leads.Where(l => l.Date.Day == date.Day
                && l.Date.Month == date.Month
                && l.Date.Year == date.Year
                && l.Property.Type == ProtectedPropertyType.Password
                && l.Property.PropertyId == PropertyId).Sum(l => l.Amount);
1
178
7/11/2013 1:40:57 PM

Accepted Answer

Try changing your query to this:

db.Leads.Where(l => l.Date.Day == date.Day
            && l.Date.Month == date.Month
            && l.Date.Year == date.Year
            && l.Property.Type == ProtectedPropertyType.Password
            && l.Property.PropertyId == PropertyId)
         .Select(l => l.Amount)
         .DefaultIfEmpty(0)
         .Sum();

This way, your query will only select the Amount field. If the collection is empty, it will return one element with the value of 0 and then the sum will be applied.

381
7/11/2013 12:36:51 PM

Popular Answer

I prefer to use another hack:

double earnings = db.Leads.Where(l => l.Date.Day == date.Day
                                      && l.Date.Month == date.Month
                                      && l.Date.Year == date.Year
                                      && l.Property.Type == ProtectedPropertyType.Password
                                      && l.Property.PropertyId == PropertyId)
                          .Sum(l => (double?) l.Amount) ?? 0;


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