Arcade: Sum of feature values in a related table

[kawakawa4]

Hi, 

I have a point layer in a web  map that I would like to symbolise using the sum of a field in a related table (1 to many join). So I have opened an expression in the 'Choose attributes' section of the Styles tab.  There are some empty values in the field so I have tried to correct that in the script.

However, I am getting an error saying: "Test execution error: Execution error - Key not found - Possums. Verify test data.". I have checked the 'Possums' field and it is an integer field, and my spelling is correct. 

Here is the script: 

var relatedRecords = FeatureSetByRelationshipName($feature, '18', ['Possums'], true);
var value = $feature['Possums'];
if (IsEmpty(value)){
  return 0
}
var sum = Sum(relatedRecords, 'Possums');
return sum;

Something that I'm not sure about is the name of the relationship class. I sourced it from here: 

is that correct, and why is my script not working please?  Many thanks

[ChristopherCounsell]

I don't believe FeatureSets are supported for symbology. Please refer to this idea (and vote for it):

https://community.esri.com/t5/arcgis-online-ideas/allow-featureset-functions-to-be-accessed-in/idi-p...

[ChristopherCounsell]

Also - just keep in mind performance. For your map to be symbolized this way, it would have to do a lot of work... better to keep FeatureSets in the pop-up I believe

[jcarlson]

One way around this is to create an attribute-based join between the two layers, which can be done using the web map's analysis tools. When a join is based on an attribute and both layers are owned by you, the resulting layer can be a "live" join, meaning it will stay up to date as the source layer is edited.

This would give you a way of symbolizing features based on related data, while still maintaining a link to the original datasets.

[kawakawa4]

Thanks @jcarlson , I have been using join views for other layers, but I can't find a way to symbolise by the sum of values in the join table using that method. Using 'aggregate' in the web map, I can get a count of aggregated features or a sum of values as a label, but not in the symbology.

An example of where I need this: I have points symbolised as pie charts and I want the pie chart to show the sum of all values from the join table related to that that point. Currently with a join view, I get several pie charts on top of each other. Or similarly, I would like the size of a point symbol to change according to the sum of all values from the join table related to that that point. Currently with a join view, I get several separate points on top of each other. 

Hopefully there is a way to do that with symbology options that I am missing!

[ChristopherCounsell]

There isn't a way within the symbology options as FeatureSets need to be supported.

You can do workaround solutions like @jcarlson suggested. Another one is to update a 'count' field in the parent table and symbolize that directly. You could potentially do that as part of your data collection workflow. Or you could schedule a python script to run regularly and update it (check related table for edits, if there is an edit, query and update the count for the parent record).