FeatuerLayer .caculate that concatenates a field with a standalone string

[CameronAndrew]

Good afternoon!

I am trying to write a short script that will periodically be run to check whether there are new rows in hosted layer. When there are new rows, I want a particular field to calculated by combing a string prefix ("NNTREE-") with the OBJECTID value. I found some past discussions on .calulate, several which managed to resolve people's problems, but none dealt specifically with trying to combine a field with a string in this way.

import arcgis
from arcgis.gis import GIS
gis = GIS("pro")
trees = gis.content.get('ebc917bcf648444a8161f4dca4afb7ec')

trees.layers[0].calculate(
    where="assetid IS NULL",
    calc_expression = {
        'field': 'assetid',
        "sqlExpression" :'CONCAT("NNTREE-", OBJECTID)'})

Exception: 
'Invalid field: NNTREE-' parameter is invalid
(Error Code: 400)

Thank you for any help.

[EarlMedina · Accepted solution]

Hey, your calc_expression value should be:

{"field": "assetid", "sqlExpression": "CONCAT('NNTREE-', OBJECTID)"}

[CameronAndrew]

That' great, thank you. I had managed a slightly more convoluted workaround to achieve the same effect, but this is preferable.  I appreciate your help!

Looks like it was just the single/double quotation marks at issue? As someone primarily accustomed to R, I need to get used to there being an important distinction between those two characters in SQL syntax.