SSRS Report Builder 3.0 - Why can't I use a code function as the source expression of a Lookup Function?

Question

I've built a report in Report Builder 3.0 that has a couple of hundred cells that perform Lookup functions in my datasets. Obviously, with the number of cells, I would like to be able to create the expressions dynamically. I've been able to utilize the textbox names to do this with the following function:

Public Function TextBoxName(ByVal meString As String) As String
 Dim s As Integer = 19
 Dim e As Integer = meString.IndexOf(“_TextBoxExprHost”) – 19
 TextBoxName = meString.Substring(s,e)
 End Function

Expression:
 =Code.TextBoxName(Me.ToString)

The above expression works as needed everywhere in the report except when I want to use it in a source expression in a Lookup function. Here is an example:

Iif(IsNothing(Lookup((Code.TextBoxName(Me.ToString) & "R"),Fields!SECTION_STATUS.Value,Fields!LCTN_COUNT.Value, "Loads")),"0",Lookup((Code.TextBoxName(Me.ToString) & "R"),Fields!SECTION_STATUS.Value,Fields!LCTN_COUNT.Value, "Loads"))

The above example will compile but produces a #Error in the cell when I run the report. But, the report works as needed if I hardcode the textbox name for each of the source expressions.

"AP1010R" instead of Code.TextBoxName(Me.ToString) & "R"

I've found no examples of anyone using custom code to generate this source expression. Anyone have any ideas what could be going on here? Thanks in advance.

Answer 1

The problem is actually not with the custom code in the source expression (try a simple custom function that only returns a string and it works fine), but specifically with the Me.ToString portion. My guess is Me is trying to reference the wrong object while inside the Lookup.

I haven't found much detailed usage for Me , but a possible workaround would be writing your own custom lookup function which is detailed nicely in this MSDN forum post . The gist of it (using Lookup function terminology):

1. Create a hidden, multi-value parameter
2. Set available and default values to destination_expression column; set labels to result_expression column

3. Add custom code:

    Function CustomLookup(id AS String) AS String Dim i As Integer i = 0 For i = 1 to Report.Parameters!YourParameter.Count() If Report.Parameters!YourParameter.Value(i) = id Then CustomLookup = Report.Parameters!YourParameter.Label(i) Exit For End If Next i End Function 

4. Call it like: =Code.CustomLookup(Code.TextBoxName(Me.ToString) & "R")

This may not be feasible/performant enough (especially if your lookup dataset is large and/or destination and result expression columns change a lot in various lookups) but it could work well in some scenarios.