Expecting ZC_SUBFORM_250 expression found COLLECTION

What?
A very quick article as I couldn't find anything on the WWW to document this error.

Why?
During a data migration, I was using a custom function to copy all the data from one app to another. The specific form was for "Leads" which contained a subform with a product line item list. If I run this code, I would get the error:

Expecting ZC_SUBFORM_250 expression found COLLECTION expression

Another error you may get when using the deluge script is:

LIST value cannot be assigned to 'mySubform'
-- or --
COLLECTION value cannot be assigned to 'mySubform'

How?
Quite simply the error is because the Creator Deluge syntax I was using to insert subform rows was wrong. Contrary to the documentation that says "This task can be used in the following events", effective as of today October 19, 2020, I have not found a place you cannot use this deluge script. The ZC_SUBFORM_250 error is because I am trying to assign the collection or list to the subform when I need to use "INSERT" twice: once to add the row to the collection, and the second time to add the collection to the subform.

Syntax for inserting a row into a subform:

// declare a variable to hold the collection of rows
<variable> = Collection();

// declaring the row
<row1> = <mainForm_linkName>.<subForm_linkName>();

// assigning values for various subform fields in the row
<row1>.<field_linkName> = <value>;
<row1>.<field_linkName> = <value>;

// insert the row into the collection
<variable>.insert( <row1> );

// insert the collection into the subform on the current form
input.<subForm_linkName>.insert( <variable> );

// or insert the row(s) into the subform through the record variable
r_LeadDetails = Leads[ID == 1234567890];
r_LeadDetails.<subForm_linkName>.insert( <variable> );

Events I have used this task which contradicts documentation:

• In a custom function
• In an Action item in Report
• In a schedule workflow

Source(s):

• Zoho Creator - Insert rows in Subform (via Deluge Script)