topic Re: Adding multiple fields to hosted feature layer in ArcGIS API for Python Questions

Adding multiple fields to hosted feature layer

JustinWolff — Thu, 06 Mar 2025 00:26:40 GMT

I'm attempting to add new fields to a hosted feature layer if they don't already exist. Currently my code will add the first field in the list (dictionary), but then fails with the message:

Exception: Unable to add feature service layer definition.
Invalid definition for System.Collections.Generic.List`1[ESRI.ArcGIS.SDS.FieldInfo]

Object reference not set to an instance of an object.

(Error Code: 400)

If it's run a second time it does not add the second field and gives the same error. I added the sleep thinking it may help but it doesn't. Any suggestions appreciated. Thanks.

from arcgis.gis import GIS from arcgis.features import FeatureLayer import time username = '' password = '' gis = GIS("<url>", username, password, verify_cert=False) item_id = "<item_id>" feature_layer_item = gis.content.get(item_id) feature_layer = FeatureLayer.fromitem(feature_layer_item) #feature_layer = FeatureLayer.fromitem(feature_url) fields = feature_layer.properties.fields existing_field_names = [field.name for field in fields] new_fields = [ {"name":"newfield1", "alias": "New Field 1","type": "esriFieldTypeInteger"}, {"name":"newfield2", "alias": "New Field 2","type":"esriFieldtypeInteger"}, {"name":"newfield3", "alias": "New Field 3","type":"esriFieldtypeInteger"} ] fields_to_add_list = [] # this is named 'list' but is actually a dictionary for new_field in new_fields: if new_field["name"] not in existing_field_names: fields_to_add_list.append(new_field) print(f"Field '{new_field['name']}' will be added.") else: print(f"Field '{new_field['name']}' already exists.") for field_to_add in fields_to_add_list: print(field_to_add) feature_layer.manager.add_to_definition({"fields":[field_to_add]}) time.sleep(20)

Re: Adding multiple fields to hosted feature layer

DavidSolari — Thu, 06 Mar 2025 00:51:21 GMT

Instead of running multiple calls to add_to_definition does doing every field in the fields_to_add_list list work better? I.e.:

feature_layer.manager.add_to_definition({"fields": fields_to_add_list})

Re: Adding multiple fields to hosted feature layer

JustinWolff — Thu, 06 Mar 2025 03:48:30 GMT

That gives the same error, except it doesn't add the first field, when left out of brackets:

feature_layer.manager.add_to_definition({"fields":fields_to_add_list})

And does not create the first field when placed in brackets:

feature_layer.manager.add_to_definition({"fields":[fields_to_add_list]})

but gives a bit different error:

Exception: Unable to add feature service layer definition.
Invalid definition for System.Collections.Generic.List`1[ESRI.ArcGIS.SDS.FieldInfo]
Unable to cast object of type 'System.Object[]' to type 'System.Collections.Generic.IDictionary`2[System.String,System.Object]'.
(Error Code: 400)

Re: Adding multiple fields to hosted feature layer

JustinWolff — Thu, 06 Mar 2025 03:57:38 GMT

and if I use field_to_add outside of any brackets it completes without any errors but doesn't add any fields

feature_layer.manager.add_to_definition({"fields":field_to_add})

with the print statements as they currently are:

Field 'newfield1' will be added.
Field 'newfield2' will be added.
Field 'newfield3' will be added.
[{'name': 'newfield1', 'alias': 'New Field 1', 'type': 'esriFieldTypeInteger'}, {'name': 'newfield2', 'alias': 'New Field 2', 'type': 'esriFieldtypeInteger'}, {'name': 'newfield3', 'alias': 'New Field 3', 'type': 'esriFieldtypeInteger'}]
{'name': 'newfield1', 'alias': 'New Field 1', 'type': 'esriFieldTypeInteger'}
{'name': 'newfield2', 'alias': 'New Field 2', 'type': 'esriFieldtypeInteger'}
{'name': 'newfield3', 'alias': 'New Field 3', 'type': 'esriFieldtypeInteger'}

Am I missing something in the field definition?

Re: Adding multiple fields to hosted feature layer

Clubdebambos — Thu, 06 Mar 2025 08:44:51 GMT

Hi @JustinWolff,

I was able to reproduce your error and fix it. Add in the full field definitions as per below.

from arcgis.gis import GIS from arcgis.features import FeatureLayer username = '' password = '' gis = GIS("<url>", username, password, verify_cert=False) item_id = "<item_id>" feature_layer_item = gis.content.get(item_id) feature_layer = FeatureLayer.fromitem(feature_layer_item) fields = feature_layer.properties.fields existing_field_names = [field.name for field in fields] ## DEFINE THE FIELDS new_fields = [ { "name": "newfield1", "type": "esriFieldTypeInteger", "actualType": "int", "alias": "New Field 1", "sqlType": "sqlTypeInteger", "nullable": True, "editable": True }, { "name": "newfield2", "type": "esriFieldTypeInteger", "actualType": "int", "alias": "New Field 2", "sqlType": "sqlTypeInteger", "nullable": True, "editable": True }, { "name": "newfield3", "type": "esriFieldTypeInteger", "actualType": "int", "alias": "New Field 3", "sqlType": "sqlTypeInteger", "nullable": True, "editable": True } ] ## REMOVE ANY FIELDS FROM THE LIST THAT ARE ALREADY IN THE FEATURE LAYER new_fields = [field_info for field_info in new_fields if field_info["name"] not in existing_field_names] ## ADD THE NEW FIELDS feature_layer.manager.add_to_definition({"fields":new_fields})

I hope that helps.

All the best,

Glen

Re: Adding multiple fields to hosted feature layer

JustinWolff — Thu, 06 Mar 2025 13:27:07 GMT

Thanks Glen, that works well. As a follow-on, my test data only has one layer [0]. I'll have other situations where there are multiple sublayers. I'm a bit confused how to use gis.content to return the separate layers. Any help pointing me in the right direction is appreciated. Thanks again.

Re: Adding multiple fields to hosted feature layer

Clubdebambos — Thu, 06 Mar 2025 14:38:40 GMT

Hi @JustinWolff,

The below will help. A Feature Service Item (FeatureLayerCollection) has a property called layers that returns a list of FeatureLayer objects for the service. You can iterate over these or access via indexing.

from arcgis import GIS ## acess ArcGIS Online agol = GIS("home") ## get the Feature Service as an Item object item = agol.content.get("FS_ITEM_ID") ## print all feature layer ## note: returns a list of FeatureLayer objects print(item.layers) ## get the index and name for each layer for index, fl in enumerate(item.layers): print(index, fl.properties.name) ## access via index fl = item.layers[1] print(fl)