The return types for the following stored procedures could not be detected

Question

While drag-drop a stored procedure in dbml file I get this error:

Unknown Return Type
The return types for the following stored

Answer 1

I also had the problem (VS 2012, SQL Server 2008R2). In my case it was a combination of the + operator and various CAST statements in the code. I haven't found a way to replace them with something VisualStudio likes, but I have come up with a workaround:

Workaround "Dummy SELECT":

• Create a dummy SELECT statement with all the fields you need to return. For example:

    select 'bla bla' as field1, 123123 as field2, 'asñfs' as field3

• Comment out your SP code and just leave the dummy SELECT in your SP.
• Add your SP in the O/R designer and save (it should do know without an error message)
• Restore your original SP (leave the dummy SELECT as a comment for future use)