Can a “Join” be detected programmatically?

Question

I have some Python code that is launched from within an ArcMap project. Any joins that the user may have created in the project must be removed in order for my code to run. Unfortunately, the code that removes a join… arcpy.RemoveJoin_management("layer1", "layer2")… also breaks some of the layer properties that are critical to my application (highlighted fields, read-only fields, etc).

If joins are removed by right-clicking the layer in ArcMap and choosing “Remove Joins” the layer properties are left intact.

If I can detect that a join exists from within my code, I will simply exit the code and display a message that the user must manually remove their joins before attempting to run the code. So… Can a Join be detected programmatically?

Answer 1

Too bad there's not a hasJoin property on the arcpy.Layer class. I think you can test for a join by looking at field names though. Here's a simple proof of concept for data in a file geodatabase:

import arcpy, arcpy.mapping as arc

def joinCheck(lyr):
  fList = arcpy.Describe(lyr).fields
  for f in fList:
    if f.name.find(lyr.datasetName) > -1:
      return True
  return False

arcpy.env.workspace = r'<path_to_your_gdb>'
mxd = arc.MapDocument(r'<path_to_your_mxd>')
lyrs = arc.ListLayers(mxd)
for lyr in lyrs:
  # ignore group layers
  if not lyr.isGroupLayer:
    hasJoin = joinCheck(lyr)
    if hasJoin:
      print '\nFound a join: %s.' % lyr.datasetName
    else:
      print '\nNo join found on %s.' % lyr.datasetName

Answer 2

I think you will find that there is no bulletproof way to do this with GP objects, you'll need to use ArcObjects and comtypes. Here's some discussion from the ESRI forums on the difficulties in checking for joins with the standard GP tools/objects: http://forums.arcgis.com/threads/21472-Testing-whether-at-table-is-joined?p=70087