Is it possible to use/access scalar functions with LINQ to SQL?

Question

We have scalar functions in our database for returning things like \"number of tasks for a customer\" or \"total invoice amount for a customer\".

We are experiment

Answer 1

LINQ-to-SQL supports use with UDFs, if that is what you mean. Just drag the UDF onto the designer surface and you're done. This creates a matching method on the data-context, marked [Function(..., IsComposable=true)] or similar, telling LINQ-to-SQL that it can use this in queries (note that EF doesn't support this usage).

You would then use it in your query like:

var qry = from cust in ctx.Custs
           select new {Id = cust.Id, Value = ctx.GetTotalValue(cust.Id)};

which will become TSQL something like:

SELECT t1.Id, dbo.MyUdf(t1.Id)
FROM CUSTOMER t1

(or there-abouts).

The fact that it is composable means that you can use the value in queries - for example in a Where()/WHERE - and so reduce the data brought back from the server (although obviously the UDF will still need to be executed in some way).

Here's a similar example, showing a pseudo-UDF at use on a data-context, illustrating that the C# version of the method is not used.

Actually, I'm currently looking at such UDFs to provide "out of model" data in a composable way - i.e. a particular part of the system needs access to some data (that happens to be in the same database) that isn't really part of the same model, but which I want to JOIN in interesting ways. I also have existing SPs for this purpose... so I'm looking at porting those SPs to tabular UDFs, which provides a level of contract/abstraction surrounding the out-of-model data. So because it isn't part of my model, I can only get it via the UDF - yet I retain the ability to compose this with my regular model.

Answer 2

I believe this MSDN documentation is what you're after (as part of this wider topic of calling user-defined functions in LINQ to SQL). Can't say I've done it myself, but it sounds right...