Modify Relationship Class Keys
I hope you're having a good day! Based on what I found, the supported workflow is to update the relationship in ArcGIS Pro and then overwrite the hosted feature layer. However, relationships can also be added or removed through the REST API by modifying the layer's service definition.
Since your related table is already configured and you only need to change the foreign key field, it may be worth investigating whether the service definition can be updated directly instead. That said, this is not an officially supported workflow. There is room for error, and you could potentially break your data, so I strongly recommend testing it on a copy first.
I've attached an image showing what these relationships look like within the layer's definition. The keyField property contains the foreign key information you would want to update. Once again, because this workflow is unsupported, there is very little documentation available. My assumption is that if a relationship can be added or removed by adding onto the service definition, it may also be possible to modify an existing one in the same way.
The most relevant information I found on this was in an older Esri Community post where a user successfully added a relationship using this approach. One important detail they noted is that the changes had to be made to the definition of each individual layer rather than to the service definition as a whole.
I hope this is some helpful food for thought. Going through ArcGIS Pro is what is recommended; it is safer, albeit inconvenient, but I wanted to let you know this seems potentially possible as well. 🙂
Thanks! @KVNSCK I was too scared to try and update the definition. So at some point I'll make a copy and try that. I was able to add a relationship to the definition using ArcGIS Notebooks. I had to repeat this for the views, as just adding it to the "parent" service and updating the view didn't bring that new relationship class into the view, and so I couldn't add it to the popup in the view until I repeated it on the view. This wasn't modifying the existing relationship class, but at least works... I think ...🤔😬😅
Oddly .tables syntax restarts the index at 0, even if the index in the feature service for the first table is like 2 or something.
This was from this post: Solved: Adding Relationship Class to Featue Service - Esri Community
I also tried to delete the mistake relationship classes, but you cannot delete when there are views. The script from here gave me an error: Deleting Relationship Class from Featue Service - Esri Community
@KVNSCK Did you find Update Definition in the supported operations? I'm wondering if there are views, if Esri does not expose that operation.😢
Oops!! Never mind - found it in admin 😅
