Finding tables related to layer using ArcPy?

Question

We have an ArcGIS map service that includes about 50 layers, and many of them have related tables. I need to build a schematic of this service that includes layer name, source feature class (or table), attributes that are included -- but I also need to find which table(s) are related to a given layer, which is where I am stuck.

I have access to the source MXD. So in theory, I can open each layer in ArcMap and look at it. But, with 50 layers, I'm looking for a Python method -- especially one that I can reuse if this MXD/service changes in upcoming months (layers or tables added/removed, e.g.) to re-create my list of referenced data.

I can use the arcpy.mapping module to list the layers/tables, but I do not know how to use it to ask about relationships to other layers/tables.

• Hornbydd: One thing you need to clarify; are the relationships in_memory and stored as the layer in the MXD (i.e you created a relationship in ArcMap and saved the mxd) or are they relationships stored in a geodatabase?
• Erica: They're apparently relationship classes in the SDE geodatabase. (I only got this MXD this morning, so had to look!)
• Hornbydd: Have a look here?
• PolyGeo: I think you should focus this question on ArcPy and if you still need to ask about the ArcGIS REST API then that could be done in a separate question.
• Erica: @Hornbydd I think a relationship class property will only work if I know there is a relationship class involved. I suppose I can get all the relationship classes in the SDE and then use a list of them to compare against the list of the feature classes that participate in the map, but that's a relatively awkward workaround unless there's nothing more direct :)

Answer 1

Here is a Python 3 script that crawls a map service and prints out all of the relationships. You should just need to change the map service url.

import urllib.request
import json
MapServiceURL = 'MapServiceUrl'
relationships = []
# Get the map service definition to get a list of the layers.
with urllib.request.urlopen('{}?f=json'.format(MapServiceURL)) as url:
 ServiceInfo = json.loads(url.read().decode())
 layers = ServiceInfo['layers']
# Function that requests the relationship property for a layer in a service.
def fetchLayerRelationships(layerId, name):
 with urllib.request.urlopen('{}/{}?f=json'.format(MapServiceURL, layerId)) as url:
 LayerInfo = json.loads(url.read().decode())
 if LayerInfo.get('relationships'):
 for relate in LayerInfo.get('relationships'):
 relationships.append((name, relate.get('name')))
# Iterate over the services layers and fetch the relationships.
for layer in layers:
 fetchLayerRelationships(layer.get('id'), layer.get('name'))
for rel in relationships:
 print(rel)