Entity Framework Min Aggregate crashes on website but runs on console app? - entity-framework

Question

I have this Linq To Entites query below. When I execute this query from a Console Application, it produces SQL and executes perfectly.
But when I execute it from a web application, I get an error message that says the Min() function is not recognized by Linq To Entites and it cannot be translated to a store expression.
It is EXACTLY the same query. Both project have the same settings (concerning EF 6) in their config files, and they reference the same assemblies.
from ce in db.CustomEvents
where ce.fld_start > DateTime.Now
group ce by ce.fld_ownerId into g
select new
{
fld_ownerId = g.Key,
next_appointement_date = g.Min(i => i.fld_start)
}
It seems this happens only when the Min aggregate is on DateTime property. I hadn't this issue when I had Min on decimals, for instance.
The error message I get when I execute this in the web site is this
LINQ to Entities does not recognize the method 'System.Nullable`1[System.DateTime]
Min[CustomEvent](System.Collections.Generic.IEnumerable`1[CustomEvent],
System.Func`2[CustomEvent,System.Nullable`1[System.DateTime]])'
method, and this method cannot be translated into a store expression.
But when I execute it from the Console app, it successfully generates the SQL statement below
SELECT
1 AS [C1],
[GroupBy1].[K1] AS [fld_ownerId],
[GroupBy1].[A1] AS [C2]
FROM ( SELECT
[Extent1].[fld_ownerId] AS [K1],
MIN([Extent1].[fld_start]) AS [A1]
FROM [dbo].[mtbl_CustomEvent] AS [Extent1]
WHERE [Extent1].[fld_start] > (SysDateTime())
GROUP BY [Extent1].[fld_ownerId]
) AS [GroupBy1]
Does anyone have a clue on what is happening?? Why the same query generates SQL when run in the console app, but fails with an exception when run in the web site??
UPDATE:
It seems that the problem was an ambiguity between two different implementations of Min<T>(this IEnumerable<T>) (.net's implementation, and our own implementation). Removing the "using OurLibrary;" namespace from the file fixed the problem.

Answer 1

After vittore's suggestion to use extension methods syntax we found that the problem was that in the web project we referenced one of our libraries that included an implementation of Min<T>(this IEnumerable<T>), and we also had the using OurLibrary.Namespace; directive in the file where the linq query was.
When we used the linq syntax, the compiler picked our implementation of Min for the query and did not throw any errors. Then, at runtime, the LINQ to Entities framework crashed because it could not recognise our implementation of Min.
from ce in db.CustomEvents
where ce.fld_start > DateTime.Now
group ce.fld_start by ce.fld_ownerId into g
select new
{
fld_ownerId = g.Key,
next_appointement_date = g.Min()
}
Here there was no compiler error.
But when we used the extension method syntax, the compiler stopped with an ambiguity error, and that's how we identified the problem.
db.CustomEvents
.Where(ce => ce.fld_start > DateTime.Now)
.GroupBy(ce => ce.fld_ownerId, ce => ce.fld_start)
.Select(g => new { g.Key, next_appointement_date = g.Min() })
Here the compiler threw an error of ambiguous call to .Min
It's weird that the compiler does not recognise the ambiguity in the Linq syntax. After all, linq is only syntactic sugar.