Question

(using Entity Framework)

when i write :

IEnumerable<string> q = customers /*EF entity*/
.Select (c => c.Name.ToUpper())
.OrderBy (n => n)

the c# compiler knows how to emit expression trees which in turn , the sql execute :

SELECT UPPER (Name) FROM Customer ORDER BY UPPER (Name)

notice also the order by clause is there

but

i saw this link :

he wrote :

IEnumerable<employee> emp = 
         dc.Employees.Where(x => x.Desc.StartsWith("soft"));
emp = emp.Take(1);

after investigating the final query he saw :

SELECT [t0].[Id], [t0].[Name], [t0].[Address], [t0].[Desc] AS [Desc]
FROM [dbo].[Employee] AS [t0]
WHERE [t0].[Desc] LIKE @p0

notice there is no top clause

why is that ?

shouldn’t Take(x) be added to the query ?

will writing it like this :

IEnumerable<employee> emp = 
         (dc.Employees.Where(x => x.Desc.StartsWith("soft"))).Take(1);

would added the TOP clause to the query being sent to SQL ?

what is going here ?

( I already know that take is not a deferred execution)

Answer 1

Extension methods such as Take() are static methods, and as such they are resolved at compile time.

The compile time type of emp is IEnumerable<employee> (because it was explicitly declared as one), so the compiler picks Enumerable.Take instead of Queryable.Take, which does not perform any query translation.

If you would have been lazy and would just have used var instead of a type name:

var emp = dc.Employees.Where(x => x.Desc.StartsWith("soft"));
emp = emp.Take(1);

it would have worked, because the compiler would have picked IQueryable<employee> for emp (because the expression you initialize it with is of that type), and thus Queryable.Take for the second call.