[GIS] Using arcpy.Exists for domains

arcgis-10.0arcpydomains

A script I made creates domains within a selected geodatabase.

I need it to not create the domains if they already exist because if they do, it gives an error saying invalid domain name.

What's the best way to check if a domain exists?

Best Answer

arcpy.Exists doesn't handle domains. The ESRI help indicates what it does handle.

So you'll need to get a list of existing domains, and then check your potential new name against the list. What version of ArcGIS are you using? 10.1 introduces a new ListDomains function.

If you're on ArcGIS 10.0, then you don't have this ListDomains. In that case I think you should go with the answer to How to check if domain already exists?, which describes how to use the workspace Describe function to check for existence.

If you're on ArcGIS 10.1, then you can try out the new ListDomains function (data access module) to get a list of existing domain names for a geodatabase, and then compare your potential new name to the list of existing names.

Something like this:

myNewDomains = ['new one', 'new two']
existingDomains = arcpy.da.ListDomains("C:/xyz/xyz.gdb")

for myNewDomain in myNewDomains:
    # check if myNewDomain already exists
    found = False
    for domain in existingDomains: 
        if domain.name == myNewDomain:
            found = True
            break
    # if myNewDomain doesn't already exist, then create it
    if found = False:
        #
        # drop in your domain-creation code
        #
    else:
        print "Domain already exists:", myNewDomain

Related Solutions

ArcPy – Listing Feature Classes with Active Domains

Python has methods for listing feature classes in a geodatabase, looping through each feature class in the list, listing fields in each feature class, and showing the domain of each field.

import arcpy

#Set workspace environment to geodatabase
arcpy.env.workspace = your_gdb

#Get list of feature classes in geodatabase
FCs = arcpy.ListFeatureClasses()

#Loop through feature classes in list
for FC in FCs:

    #List fields in feature class
    fields = arcpy.ListFields(FC)

    #Loop through fields
    for field in fields:

        #Check if field has domain
        if field.domain != "":

            #Print feature class, field, domain name
            print FC, field.name, field.domain

The above code should work in ArcGIS 10 and it will print a list right in the python interpreter window. You can then copy and paste the list into a text editor or Excel to review the results more easily.

ArcPy Domains – Checking If Domain Already Exists

The domains workspace property returns a Python list. If there are no domains in the workspace, then the list is empty:

>>> desc3 = arcpy.Describe(r'D:\Temp\NcLidar.gdb')
>>> domains3 = desc3.domains
>>> domains3
[]

If you have one domain, you get a list with a single element:

>>> desc2 = arcpy.Describe(r'D:\Projects\GDBs\scratch.gdb')
>>> domains2 = desc2.domains
>>> 
>>> print domains2
[u'HU_Type Domain']

You could just check the length of the list and go from there:

>>> if len(domains3) > 0:
...     print "we have domains"
... else:
...     print "no domains"
... 
no domains

Regarding the weirdness with the Exists function, it does the same thing for me. Perhaps Exists doesn't work for domains?

>>> if not arcpy.Exists(domains3):
...     print domains3
... 
[]

>>> if  arcpy.Exists(domains3):
...     print domains3
... 
>>> 
>>> if  arcpy.Exists(domains2):
...     print domains2
... 
>>> if not arcpy.Exists(domains2):
...     print domains2
... 
[u'HU_Type Domain']

>>>

Best Answer

Related Solutions

ArcPy – Listing Feature Classes with Active Domains

ArcPy Domains – Checking If Domain Already Exists

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