Thursday, 19 March 2015

Lookup Tables and a Little Chat - Getting the Type Name into a Text Parameter

I've very recently been looking at using Revit lookup tables for structural families. These are traditionally used in the MEP side of things, but I have been looking for a structural application for a while. In the course of this, one of the things I have been able to achieve is to pass the lookup table's first column 'Type Name' to a text parameter in the family. As my knowledge of lookup tables is relatively new, I assumed this was something widely used and known. At the last London Revit User Group meeting, I was chatting to Jose Fandos of Andekan and we got onto the subject of this. He assures me that it most certainly isn't and people would be interested in this little tip. So here goes:

I created a sample lookup table as follows:

In Revit, the parameters in the test family:

A text parameter is created in the family called 'Type Name'.  The formula is broken down as follows:
  • size_lookup                   
Tells Revit it's a lookup command
  • (Lookup Table,              
Refers to the lookup table name in the 'Lookup Table' parameter
  • "",                                 
Usually there is a value between the quotation marks. This refers to which column to reference in the lookup table, but in this case  we create a 'null' value. This is what allows this method to work
The text value that is used if there is no matching value in the lookup parameter
  • Size)
the lookup parameter value for the lookup formula to reference.
I'm not sure why this actually works, but I suspect that even though the syntax for the formula is correct for a lookup, the omission of a search column reference means it returns the first value it comes across, which is the 'Type Name' in the first column.
Hope this is useful.