How do you reference another field from a related table in Arcade?

[deleted-user-TRj-mR_qEmwV]

Through a Web Map in ArcGIS Online, I'm creating a field in Feature #1 and Feature #1 is related to Feature #2.  Is there a way to get the specific values in Feature #2 that are related via for an Arcade expression in Feature #1?

It's a 1 to many relate and related through a Text ID Field that they both have. 
EDIT: I think it has something to do with FeatureSetBy functions

[XanderBakker]

Hi joe rodmey , 

Do you want to write that value ("NA") to your attribute table or you just want the pop-up to show "NA" when there is no value?

[joerodmey]

Xander Bakker‌ I would like to write the value of "NA" to my attribute table in AGOL

[XanderBakker]

Hi joe rodmey ,

In that case you can use a Field Calculation to do this. 

When(IsEmpty(feature$.YourFieldName), "NA", feature$.YourFieldName);‍

The IsEmpty function will check for Null values or empty strings and when it finds such a value it will return "NA". 

Since with the Field Calculation you potentially overwrite existing data, you can best add another field to test the expression.

[joerodmey]

Would this automatically occur when new related data rolls in? The reason I need this is that Collector is automatically adding in blank records and I need a way to handle these.

[XanderBakker]

Hi Joerodney ,

Unfortunately not. This can be achieved with ArcGIS Enterprise and Attribute rules or not allowing the users to generate empty fields in Collector (field value required and use default NA and/or a domain).

[joerodmey]

How can I make certain fields required in Collector or default to NA?

[XanderBakker]

Hi Joerodney ,

Good question. There is a thread from almost a year ago mentioning that the default values are not taken correctly in Collector. Not sure if that is still the case. The thread I mentioned offers a alternative way to have the default values working correctly: Default Values in Collector 

[joerodmey]

I had a look but unsure if this will work as my feature service was created in Survey123

[joerodmey]

HI Xander Bakker‌

How can I take the code you provided earlier and return the value of zero only if the related record doesn't have a value entered?

Thanks

[XanderBakker]

Hi joe rodmey ,

If this value should appear in the pop-up, you can do this without a problem. If this should be written to the hosted service you can also, but you need to use a Field Calculation (and repeat this when the data is updated. The code would be more similar to the one posted before (using the FeatureSetByName and Filter option). Based on the count you would return the value.