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 experimenting and looking to try to do this w/o stored procedures … normally we would just call this function in our stored procedure and return it as a single value.

Is there a way to use or access scalar functions with LINQ to SQL? If so, I would be interested in see an example of how to … if not, how would it be best to handle this type of situation … if it is even doable.

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.