Extract domain from ArcGIS Online feature service using Python API

Question

I have a feature service with several coded value domains that I'm accessing as a spatially enabled dataframe using the python API.

As far as I can tell, the dataframe only holds the code for each field. I'd like to update those to the description from the domain. Is there a way to access the domain of the feature service through the API?

Answer 1

I am not aware of a functionality in the ArcGIS API for Python to accomplish this. However, you can do a workaround and get the values by querying the domains of the feature service using the ArcGIS REST API.

Using Python you would simply make the following request:

import requests

url = 'https:// <featureservice-url>/queryDomains'
params = {'f': 'json', 'layers': [1]}

r = requests.get(url, params)
data = r.json()

If the request was made correctly, data should be a dictionary similar to this one (adapted from the documentation linked above):

{
 "domains": [
  {
   "type": "codedValue",
   "name": "CDOM_3",
   "fieldType": "esriFieldTypeInteger",
   "codedValues": [
    {
     "name": "code 100 description",
     "code": "code 100"
    },
    {
     "name": "code 200 description",
     "code": "code 200"
    },
    {
     "name": "code 300 description",
     "code": "code 300"
    }
   ],
   "mergePolicy": "esriMPTDefaultValue",
   "splitPolicy": "esriSPTDefaultValue"
  }
 ]
}

It should then be rather straight forward to replace the coded values with their respective descriptions in the DataFrame. However, if it is not the case and you have trouble, leave a comment and I'll gladly update my answer.

Answer 2

The Python API has a query_domains method for Feature Layer Collection objects. In order to use this the Feature Service requires a supportsQueryDomains property set to true. I have been unable to add/set this property for a Hosted Feature Service in AGOL. It does exist, however, in a referenced Feature Service in Portal i.e. data stored in SDE. The below code uses the the query_domains method on a Portal item

from arcgis import GIS
from arcgis.features import FeatureLayerCollection

agol = GIS("home")

item = agol.content.get("**fs_id**")
flc = FeatureLayerCollection(item.url, agol)
domains = flc.query_domains(layers=[2])

print(domains)

The output is a list of dictionaries containing properties for each domain. Here is an example of a dictionary in the list.

{
    'type': 'codedValue',
    'name': 'Domain_Name',
    'description': '',
    'codedValues': [
        {   'name': 'Description1',
            'code': 1
        },
        {   'name': 'Description2',
            'code': 2
        },
        {   'name': 'Description3',
            'code': 3
        }
    ],
    'fieldType': 'esriFieldTypeSmallInteger',
    'mergePolicy': 'esriMPTDefaultValue',
    'splitPolicy': 'esriSPTDefaultValue'
}

Attempting to run this code on a Hosted Feature Service on AGOL results in an error.

The requested layer (layerId: queryDomains) was not found.
(Error Code: 400)

We can access the layer properties and extract the domain information for a Hosted Feature Service. The code below will print out a list of dictionaries similar to the query_domains method used in Portal.

from arcgis import GIS
from arcgis.features import FeatureLayerCollection

agol = GIS("home")

item = agol.content.get("**fs_id**")

## list to hold the domain information
domains_list = []

## get domains for specific layer
for fld in item.layers[0].properties.fields:
    if fld.domain:
        ## append each domain into the list
        if fld.domain not in domains_list:
            domains_list.append(fld.domain)

print(domains_list)