How to use relationship info to find feature layers in web map service?

[NickToscano]

In the docs it says:

" You may add one or more layer items to compose a web map or web scene item. Whenever you perform such an operation, you establish a relationship between the items."

I take this to mean that each web map should have a relationship to any layers that have been added to it.

However it seems that if I try to check a map that has a single feature layer, and a publicly hosted basemap I always get the following error for both dependent_to() and dependent_upon() methods:

Unable to get dependents to: 2f1071ac3228427289a6e03d2b625995 Unable to retrieve item dependents.

When I try 

webmap_item.related_items('Map2FeatureCollection', 'forward')

It returns an empty array/list.

What are the limitations of these methods? Do they not work if any of the layers are hosted on a public ArcGIS Server? How about an ArcGIS Server that has security setup?

I tried dependent_to on several feature layers and also received the same error.

[SethLewis1]

I'm also running into this error message when attempting to map out relationship between portal items, in this case a web map and a layers in the map.

zoningItem.related_items('Map2FeatureCollection', 'forward')‍

returns an empty array

While running the dependent_upon or dependent_to methods returns:

Unable to get dependencies for item: item#
Unable to retrieve item dependencies.
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-3-2b1d726173d1> in <module>()
----> 1 zoningItem.dependent_upon()

/opt/conda/lib/python3.5/site-packages/arcgis/gis.py in dependent_upon(self)
   2993     def dependent_upon(self):
   2994         """ Returns items and urls, etc that this items depends upon  """
-> 2995         return self._portal.get_item_dependencies(self.itemid)
   2996 
   2997     def dependent_to(self):

/opt/conda/lib/python3.5/site-packages/arcgis/_impl/portalpy.py in get_item_dependencies(self, itemid)
   1124 
   1125     def get_item_dependencies(self, itemid):
-> 1126         return self.con.post('content/items/' + itemid + '/dependencies', self._postdata())
   1127 
   1128     def get_item_dependents_to(self, itemid):

/opt/conda/lib/python3.5/site-packages/arcgis/_impl/connection.py in post(self, path, postdata, files, ssl, compress, is_retry, use_ordered_dict, add_token, verify_cert, token)
    954                 elif errorcode == 498:
    955                     raise RuntimeError('Invalid token')
--> 956                 self._handle_json_error(resp_json['error'], errorcode)
    957                 return None
    958         except AttributeError:

/opt/conda/lib/python3.5/site-packages/arcgis/_impl/connection.py in _handle_json_error(self, error, errorcode)
    974 
    975         errormessage = errormessage + "\n(Error Code: " + str(errorcode) +")"
--> 976         raise RuntimeError(errormessage)
    977 
    978 class _StrictURLopener(request.FancyURLopener):

RuntimeError: Unable to get dependencies for item: item#
Unable to retrieve item dependencies.
(Error Code: 500)
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[SethLewis1]

Bumping this to see if anyone has developed a solution when facing this issue.

[Anonymous User]

Was this ever resolved?

[SethLewis1]

I spoke with an ESRI staffer at the UC last summer and he clarified that item relationships must be declared for each item in the portal. I think that would explain the errors mentioned above. I thought that behind the scenes ESRI was graphing the item dependencies and exposing them via the relationship method but that appears to not be the case.

[RobertWeber]

They make very little mention of needing to establish these relationships.  It is implied in the documentation that for Web Map Items in particular it is done in the background.  I only get empty results on any of the three methods.