Using external assembly's method's results as a dataset - reporting-services

Question

Using SQL2008R2:
I am trying to create a dataset that is simply the result of an external assembly's return method(s), but everything I can find regarding using custom/external assemblies just has a textbox's value set to the external assembly's method's result via an expression.
I simply want Report Server to do the data processing in the external assembly and bind that result to a very simple report.
I found some references to something about MDX but they seem to be a few years outdated and needed to know if this is possible.

Answer 1

Assuming you already have a .dll - Place your dll in the report designer folder (where your RDL is) and the report server folder, somewhere around here:
Program Files\Microsoft Visual Studio 8\Common7\IDE\PrivateAssemblies
Program Files\Microsoft SQL Server\MSSQL.3\Reporting Services\ReportServer\bin
Now add a reference to your dll from your report.
With your report open go to Report, Report Properties, References, Add reference, browse to your dll and add it.
Now in a text box properties Value call a method of your dll. It should look something like this:
=MyDllName.ClassName.MyMethodOrSubOrWhatever
This is a great article that can walk you through this:
Assuming you already have a .dll - Place your dll in the report designer folder (where your RDL is) and the report server folder, somewhere around here:
Program Files\Microsoft Visual Studio 8\Common7\IDE\PrivateAssemblies
Program Files\Microsoft SQL Server\MSSQL.3\Reporting Services\ReportServer\bin
Now add a reference to your dll from your report.
With your report open go to Report, Report Properties, References, Add reference, browse to your dll and add it.
Now in a text box properties Value call a method of your dll. It should look something like this:
=MyDllName.ClassName.MyMethodOrSubOrWhatever
This is a great article that can walk you through this: http://support.microsoft.com/kb/920769
P.S. Another option, if you don't want the web server doing the heavy lifting, is to use stored procedures. However, in our experience with very large database systems, it is much easier to scale up the web servers than it is to scale up the database servers so we do much of the heavy lifting on the web servers.

Answer 2

If you need a data set that is generated by custom .NET code, you can either set up a web service (here's a good tutorial), or you can set up a custom "data processing extension".
A data processing extension will allow you to choose a new data source in the SSRS report designer, and this data source will run custom .NET code. The full description is on MSDN, but here are the basic steps:
Create a new class library project
Implement all of the required extensions (and any desired optional ones)
Copy the DLL to the SSRS bin folder
Edit the SSRS config file to register your extension (by specifying the fully qualified name of your IDbConnection class)
You can find working examples from both CodePlex and Microsoft.