Checking in multiple lists if a subscriber exists

Question

I am creating a publication centre using which a user can opt-in for a list. For this purpose, I have to initially check if the subscriber already exists in a list or not. I am using the following code to check whether he is a part of the list or not.

 %%[
var @rr1, @sfp4, @sfp5, @cf0, @LookUpSub, @RowCountSub
SET @rr1 = CreateObject("RetrieveRequest")
   SetObjectProperty(@rr1, "ObjectType", "ListSubscriber")
   AddObjectArrayItem(@rr1,"Properties","ListID") 
   AddObjectArrayItem(@rr1,"Properties","SubscriberKey")

SET @sfp4 = CreateObject("SimpleFilterPart")
   SetObjectProperty(@sfp4, "Property", "SubscriberKey")
   SetObjectProperty(@sfp4, "SimpleOperator", "equals")
   AddObjectArrayItem(@sfp4, "Value",@sub_ID)

SET @sfp5 = CreateObject("SimpleFilterPart")
   SetObjectProperty(@sfp5, "Property", "ListID")
   SetObjectProperty(@sfp5, "SimpleOperator", "equals")
   AddObjectArrayItem(@sfp5, "Value",@lis_ID)
   
Set @cf0 = CreateObject("ComplexFilterPart")
   SetObjectProperty(@cf0,"LeftOperand",@sfp4)
   SetObjectProperty(@cf0,"RightOperand",@sfp5)
   SetObjectProperty(@cf0,"LogicalOperator","AND")

   SetObjectProperty(@rr1, "Filter", @cf0)
   SET @LookUpSub = InvokeRetrieve(@rr1)
   SET @RowCountSub = Rowcount(@LookUpSub) 
]%%

This is inside a for loop checking for every list. But when I run this I get an error.

ExactTarget.OMM.InvalidScriptException: The function expression is invalid. See inner exception for detail.
Script: ContentBlockByName(@contentAreaPath)\r\n Index: 4342\r\n ListID: 0\r\n Error Code: OMM_FUNC_EXPR_INVALID
- from Jint --> 
 --- inner exception 1---
ExactTarget.OMM.FunctionExecutionException: An error occurred when attempting to evaluate a ContentBlockByName function call.
Function Call: ContentBlockByName(@contentAreaPath)
See inner exception for details.
Error Code: OMM_FUNC_EXEC_ERROR
- from OMMCommon --> 
 --- inner exception 2---
ExactTarget.OMM.InvalidScriptException: The function expression is invalid. See inner exception for detail.
Script: AddObjectArrayItem(@sfp5, \"Value\",@lis_ID)
Index: 839
ListID: 0
Error Code: OMM_FUNC_EXPR_INVALID
- from OMMCommon --> 
--- inner exception 3---
nExactTarget.OMM.FunctionExecutionException: An error occurred when attempting to evaluate a AddObjectArrayItem function call. See inner exception for details.
Error Code: OMM_FUNC_EXEC_ERROR
- from OMMCommon --> 
--- inner exception 4---
System.InvalidCastException: Object cannot be stored in an array of this type. - from mscorlib

This is because I am guessing I cannot reuse the same variable names for different search purposes. I looked around and I found that declaring variables like var @xyz can empty or flush the previously existing values but it's not working here. Is there a work around this issue or something that can resolve the problem? Thank you for your help.

Answer 1

If we are sticking to AMPScript, rather then do all that with API - you can also just do a Lookup to the _ListSubscriber Data View which should have all the lists a person is on. As this is on a Cloudpage and not an email, the delay/extra processing should not be significant and likely less then the AMPScript API route.

I would first do a lookup to get all the publication lists associated with that subscriberKey:

SET @LURows = LookupRows("_ListSubscribers","SubscriberKey", AttributeValue("_subscriberkey"), "ListType","Publication List")

Then you would iterate through this creating a modified delimited list:

SET @listStr = "|"
FOR @i=1 TO Rowcount(@LURows) DO
  SET @row = ROW(@LURows,@i)
  SET @listName = FIELD(@row,"ListName")
  SET @listStr = CONCAT(@listStr,@listName,"|")
NEXT @i

This will generate something like |list1|list2|list3| etc.

Then in order to check if they exist on a publication list, you can just do an IndexOf() against this string to verify.

For example, if you want to see if the person is on list2 then you would do:

IF INDEXOF(@listStr,CONCAT("|","list2","|")) > 0 THEN
  set @list2  = 1
ENDIF

This will search for the value of |list2| inside the modified delimited string. This will remove any partial value matches as each will start and end with a pipe | forcing only exact matches.

If you still wanted to use the API, I would instead shift to using WSProxy via SSJS as there are a lot more options there and it is a ton more performant for this task.