Expose `op` to update custom metadata fields on items

[jonocarroll]

I am trying to update some custom metadata of a sharepoint item (additional columns added, not just "name") with this package. I am able to achieve this via the mgc cli with e.g.

mgc sites lists items fields patch --list-id $listID --site-id $siteID --list-item-id 5 --body '{"metadataValue": "123"}'

With AzureGraph, following this workflow:

gr <- get_graph_login()
site <- gr$get_sharepoint_site(sp_url)
lists <- site$get_lists()[[1]]
item <- lists$get_item(5)
item$update("metadataValue" = "123")

the path that is constructed does not include the "fields" path. It appears that the op argument to do_operation() would be where this could/should be set, but this is not exposed to the outer update() function

AzureGraph/R/ms_object.R

Lines 81 to 86 in 983aaaa

	update=function(...)
	{
	self$do_operation(body=list(...), encode="json", http_verb="PATCH")
	self$properties <- self$do_operation()
	self
	},

...

AzureGraph/R/ms_object.R

Lines 113 to 117 in 983aaaa

	do_operation=function(op="", ...)
	{
	op <- construct_path(private$api_type, self$properties$id, op)
	call_graph_endpoint(self$token, op, ...)
	},

Could this be modified to update(op="", ...) (or some other equivalent approach)? It is difficult to inject this since the class is R6, but my workaround for the moment is

field_update <- function(obj, ...) {
  obj$do_operation(op = "fields", body = list(...), encode = "json", http_verb = "PATCH")
}
field_update(item, "metadataValue" = "123")