This method will return the fabrication id for the given reference. 
   Namespace:   Autodesk.Revit.DB.Steel  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 22.0.0.0 (22.1.0.0) 
  Since:  2019 
Syntax
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Parameters
- aDoc
 -  Type:  Autodesk.Revit.DB Document  
Document to which the reference belongs. 
- reference
 -  Type:  Autodesk.Revit.DB Reference  
The reference to the element or subelement for which fabrication id is required. 
Return Value
The fabrication id of the element or subelement for this reference, if it has fabrication information attached, or an Guid.Empty otherwise.Exceptions
| Exception | Condition | 
|---|---|
| Autodesk.Revit.Exceptions ArgumentNullException | A non-optional argument was null |