Searching for value in layer without opening MXD file?

Question

As part of the validation for parameters of a Python toolbox, I need to check if the text in parameter #1 is exists in a layer in a MXD file selected as parameter #2. Currently, I use this code in updateMessages:

mxd = arcpy.mapping.MapDocument(parameters[2].valueAsText)
layer = arcpy.mapping.ListLayers(mxd, "LayerName")[0]
condition = u"Field=" + parameters[1].text
with arcpy.da.SearchCursor(layer.dataSource, ["Field"], condition) as cursor:
    #Do some stuff...

The problem is that this takes very long time since the rather large MXD file has to be opened. It is not acceptable to have a two minute waiting time with ArcMap freezing every time the parameter validation is performed.

So my question is this: Is there any way to find the source of the layer, and search for a value in it, without having to open the MXD?

Answer 1

Unless your layer definitions are static enough that you can keep them also saved as layer files, then I think you are stuck with creating a MapDocument object in order to locate its layer definitions.

If you are able to use a layer file instead of using a map file to get at the layer definitions then just use the specific Layer object instead of creating a MapDocument object, and it should be much quicker.