How to assign value to field using Arcade calculated value

[OliverIshmael]

I wish to pre-populate the a field (Survey_Type) in my form with a Domain value "Asset" and have been attempting to do this using an Arcade expression. The expression returns false, and the value isn't added:

$feature.Survey_Type == "Asset"

What am i doing wrong?

[JeffSilberberg]

Two equal signs is a comparison -- One equal is an assignment 

If you want to assign the vale then I think you want -- $feature.Survey_Type = "Asset"

[OliverIshmael]

Unfortunately, I already tried that. In red text Field Maps form says:

'Failed to calculate'

[ARCADE] - Expression failed to evaluate: \nName: expr/survey-type--asset\nError:java.util.concurrent.ExecutionException:com.esriarcgisruntime.ArcGISRuntimeException:Arcade expression is invalid.: Arcade evaluation error. Evaluation_error_code::cannot_assign_to_const_value Line:1

[JustinReynolds · Accepted solution]

You can not assign a value to a field in this way. $feature.[any field name] is a constant during the execution of any expression.  All you need to do is return the string "Asset". 

In designer, select the field Survey_Type. Then add a field calculation. 

return "Asset"

Here is some helpful documentation. 
https://developers.arcgis.com/arcade/guide/variables/

https://developers.arcgis.com/arcade/guide/return/

[RhettZufelt]

You might need to return the Domain Code and not the value.

You could also just set "Asset" as the default value in the template.

R_

[OliverIshmael]

@JustinReynolds @RhettZufelt I tried both of your suggestions (using calculated values, or, using default value) but neither of them result in a value being added to the field. The form completes successfully, but when i view the feature layer data no value has been saved for that field.

Do you know why this might be?

[JustinReynolds]

Can you provide more details, I'd prefer not guess.

Please post your expressions in a JavaScript code block or screenshot it. Screenshot the Form as it is being completed, the popup afterword and the feature layer data you say is not being populated.

A screenshot of the field with its domain values would also be helpful.

Also, when you create the expression does it work when you test it in Field Maps Designer?

[OliverIshmael]

Thank you for offering to help. Bizarrely it wasn't working yesterday but it is now. So that's good...i think?!