Question

We are implementing some EF data repositories, and we have some queries which would include TOP 1

I have read many posts suggesting to use .Take(1)
The code I’m reviewing uses .First()

I understand that both of these produce the same result for the object assignment, but do they both actually resolve to the same query? When the DB is queried, will it actually be with TOP 1 for both requests? Or will they execute the query in full into the enumerable, then simply take the first entry in the collection?

Furthermore, if we used .FirstOrDefault() then why should we expect any different behavior? I know that when using an IEnumerable, calling .First() on an empty collection will throw, but if this is actually only changing the query to include TOP 1 then I should expect absolutely no functional difference between .First() and .FirstOrDefault()…. right?

Alternatively, is there some better method than these Enumerable extentions for making the query execute TOP 1?

Answer 1

From LINQPad:

C#:

age_Centers.Select(c => c.Id).First();
age_Centers.Select(c => c.Id).FirstOrDefault();
age_Centers.Select(c => c.Id).Take(1).Dump();

SQL:

SELECT TOP (1) [t0].[Id]
FROM [age_Centers] AS [t0]
GO

SELECT TOP (1) [t0].[Id]
FROM [age_Centers] AS [t0]
GO

SELECT TOP (1) [t0].[Id]
FROM [age_Centers] AS [t0]

*Note that Take(1) enumerates and returns an IQueryable.