How to enforce Primary Key Uniqueness on a ADODB.Recordset created from scratch?

I am using a recordset as a vehicle for some data that I am acquiring. I am getting duplicates and I was curious as to how to get the recordset to complain if an attempt to add a duplicate is made.

So, essentially I want to create a key field. I have found the adFldKeyColumn parameter but it is not enforced, I must be missing something.

Function CreateIndexedRecordSet() As ADODB.Recordset
    Dim rs As ADODB.Recordset
    Set rs = New ADODB.Recordset
    rs.Fields.Append "Name", adBSTR, 255
    rs.Fields.Append "pkey", adInteger, , adFldKeyColumn
    rs.Open

    rs.AddNew Array("Name", "pkey"), Array("foo", 1)
    rs.AddNew Array("Name", "pkey"), Array("bar", 1)  '<--- this should complain

    Debug.Print rs.Supports(CursorOptionEnum.adIndex) '<--- sadly prints False, perhaps use a different provider?

    Set CreateIndexedRecordSet = rs
End Function

Please no triage answers, I know full well I can use a Dictionary whilst I acquire the data and catch duplicates that way, that is what I will do in the meantime. It's just there must be an ADO expert out there who knows the trick.

UPDATE: I have found a Supports method on the RecordSet object, if I pass in CursorOptionEnum.adIndex then it replies False. Perhaps use a different provider?

Solution

This can't be achieved, as noted by @AlexK

ADODB recordsets don't support constraints of itself. It's the database that enforces constraints, not the recordset. If your recordset is not updating to a database, there are no constraints.

To demonstrate this behavior, you can test the following in Access:

Create a table named Table1 with 2 fields (ID, primary key, Field1, string)

Run the following code:

Dim rs As New ADODB.Recordset
Dim conn As ADODB.Connection
Set conn = CurrentProject.Connection
conn.CursorLocation = adUseClient
rs.Open "SELECT * FROM Table1", conn, adOpenKeyset, adLockBatchOptimistic 'Open up recordset
Set rs.ActiveConnection = Nothing 'Disconnect it from the database connection
rs.AddNew Array("ID", "Field1"), Array(1, "A") 'Add a record
rs.AddNew Array("ID", "Field1"), Array(1, "A") 'And another identical one
Set rs.ActiveConnection = conn
'All fine until here, recordset contains 2 records with identical primary key
rs.UpdateBatch 'Errors, duplicate primary key

Of course, you can manually check for duplicates yourself, or set a handler on the Recordset_WillChangeRecord event to enforce constraints, but you said you weren't interested in that.

_{can't be done answers are allowed per Is “this is not possible” an acceptable answer?}