How can I check if a doc exists in Knowledge Center within a process?

Question

I have a process that gets a Doc ID to be deleted from the database. Before attempting to delete the doc, I would like to check if it exists in Knowledge Center? How can I do so? 
 See below highlighted node where I need to add this "Check". 
 Docs to be deleted node returns a list of Documents. 
 Check needs to search for IDs as an array, if not found, remove from array.

ujjwalr0002 · Answer

To check the knowledge center ID for documents you can use the document function we have a property as knowledgeCenterId once you have the IDs you can use whereContains and index functions to get the filtered list.

Mike Schmitt · Answer

Can you clarify what you mean by this? 
 hunterr0001 said: check if it exists in Knowledge Center 
 Are you saying it should be in some specific knowledge center , and if it isn't in that specific knowledge center, then don't delete it? Or are you merely saying you want to check that it's a valid document ID within Appian ? Since all documents are in *some* knowledge center to begin with. 
 Honestly the best place to do this might be in the code you're using for the "Docs to be Deleted" node - especially if you're handling that output with an expression rule where you can easily test different scenarios.

Mike Schmitt · Answer

There are various ways to take a doc ID and check that it represents a valid document in the system - one of the easier current ways that I actually use is the function "isobjectexists()" found in the Check Objects Existence plug-in . I wrap this function in an expression rule that I call something like "APP_Util_docExists()", where i also check that the input ID is non-empty and non-zero before calling the plug-in function on it. and(
 a!isNotNullOrEmpty(ri!doc),
 tointeger(ri!doc) > 0,
 
 isobjectexists("Document", ri!doc)
)