How do I check if a subscriber exists in a list using ampscript on a landing page?

Question

I am creating a custom subscription center and I have been able to include a subscriber to a publication list when they unsubscribe from it with an unsubscribe status. I need to ensure that when they re-subscribe to the publication list, they get removed from the list instead of changing the status to active. (We do not want them to get all emails for that publication, just the suitable emails.)

If they appear on the publication list they will be removed with the following code:

        /* CHECK TO SEE IF THE SUBSCRIBER HAS SUBSCRIBED. IF SO, DELETE OFF PUBLICATION LIST IF THEY ARE IN THERE*/
    
    IF (RequestParameter(@PublicationType)=="True" AND @SubscriberPublicationList == "N" AND @existPubList == "True") THEN
    
    SET @rr = CreateObject("RetrieveRequest") 
    
    SetObjectProperty(@rr, "ObjectType", "List")
     AddObjectArrayItem(@rr,"Properties","ListName") 
     AddObjectArrayItem(@rr,"Properties","ID")
    
    SET @sfp = CreateObject("SimpleFilterPart")
     SetObjectProperty(@sfp, "Property", "ListName")
     SetObjectProperty(@sfp, "SimpleOperator", "equals")
     AddObjectArrayItem(@sfp, "Value",@PublicationType)
     SetObjectProperty(@rr, "Filter", @sfp) 
    
    SET @Sub = InvokeRetrieve(@rr) 
    
    Set @ListID = Field(Row(@Sub,1),"ID")
    
    SET @ll_sub = CreateObject("Subscriber")
    SetObjectProperty(@ll_sub, "EmailAddress", @EmailAddress)
    
    SetObjectProperty(@ll_sub, "SubscriberKey", @subKey)
    
    
    set @subscription = CreateObject("SubscriberList")
    SetObjectProperty( @subscription, "ID",@ListID)
    SetObjectProperty( @subscription, "IDSpecified", "true" )
    SetObjectProperty( @subscription, "Status", "Active" )
    SetObjectProperty( @subscription, "StatusSpecified", "true" )
    AddObjectArrayItem( @ll_sub, "Lists", @subscription )
    
    SET @ll_statusCode = InvokeDelete(@ll_sub, @ll_statusMsg, @errorCode)
    
    IF @ll_statusCode != "OK" THEN
        RaiseError(@ll_statusMsg, 0, @ll_statusCode, @errorCode)
    ENDIF
    
    ENDIF

NEXT @cnt 

ENDIF

When I run this and a person is not on the list to begin with, it will give me the following error:

Error code: 13007

Status Code: Error

NotOnList

That makes sense! My question is how do I check to see if the subscriber is on the list. Once I know this, I can update my if statement to only run when they were only in this list (@existpubList == "True"). I think This needs to be done with a simpleFilterPart but I don't understand objects enough to get it to work.

I appreciate any help with this. Many thanks!

---

Based on Timothy's suggestion, I have tried to use an InvokeRetrieve to find out if a subscriber key exists in the list but I can't seem to get it to work. I have written the code below:

/* USE LOOK UP TO FIND SUBSCRIBER KEY IN LIST USING SIMPLEFILTERPART AND COMPLEXFILTERPART*/

SET @rr8 = CreateObject("RetrieveRequest") 

SetObjectProperty(@rr8, "ObjectType", "ListSubscriber")
 AddObjectArrayItem(@rr8,"Properties","ListID") 
 AddObjectArrayItem(@rr8,"Properties","SubscriberKey")

SET @sfp8 = CreateObject("SimpleFilterPart")
 SetObjectProperty(@sfp8, "Property", "ListID")
 SetObjectProperty(@sfp8, "SimpleOperator", "equals")
 AddObjectArrayItem(@sfp8, "Value",@ListID)


SET @sfp9 = CreateObject("SimpleFilterPart")
 SetObjectProperty(@sfp9, "Property", "SubscriberKey")
 SetObjectProperty(@sfp9, "SimpleOperator", "equals")
 AddObjectArrayItem(@sfp9, "Value",@subKey)


Set @cf1 = CreateObject("ComplexFilterPart")
    SetObjectProperty(@cf1,"LeftOperand",@sfp8)
    SetObjectProperty(@cf1,"RightOperand",@sfp9)
    SetObjectProperty(@cf1,"LogicalOperator","AND")

SetObjectProperty(@rr8, "Filter", @cf1)

SET @LookUpSub = InvokeRetrieve(@rr8) 

SET @RowCountSub = Rowcount(@LookUpSub)

IF (RequestParameter(@PublicationType)=="True" AND @SubscriberPublicationList == "N" AND @RowCountSub > 0) THEN

I get the following error:

The function expresion is invalid. See inner exception for detail.

Script: AddObjectArrayItem(@sfp8, "Value",@ListID)

Index: 10928

ListID: 1317684.

Am I using the wrong object for this InvokeRetrieve?

Many thanks!

Answer 1

You will need to create another lookup using InvokeRetrieve for the list of interest. Then, on the rowset you get back, you will call the method RowCount... if it is greater than 0, the subscriber is on the list.

Good luck!

Answer 2

The LinkID is numeric. Try FormatNumber(@LinkID,"G")