Question

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The query results cannot be enumerated more than once?

I am using entity framework to select and return a group of entities form my database using a stored procedure.

var results = dataContext.loadData(testargument);

I want to count this returned set (to make sure only 1 record is returned and then take the first item in this list.

if(results.Count() == 1)
{
    ReturnedEntity entity = results.First();
}

However when I do this call I get the error “The result of a query cannot be enumerated more than once.” Does anyone know how I can do this correctly? I assume that calling the Count() method is changing the data and am not sure if I need to put it back into a list before calling the first() method. I have tried results.ToList().First() but get the same error.

In addition I notice that if I call the First() method on an empty set I get an error which is why I am trying to make sure there is only 1 record returned.

Answer 1

You can avoid this problem using ToList(). Becuase then when you have the list loaded in your memory you can do whatever you want. But I reccomend you use FirstOrDefault().

var results = dataContext.loadData(testargument).ToList();

And

ReturnedEntity entity = results.FirstOrDefault();

Or

if(results.Length == 1)
    ReturnedEntity entity = results.First();