[GitHub] [couchdb] garrensmith commented on a change in pull request #2904: Add support for previous bookmark

[GitBox <gi...@apache.org>]

garrensmith commented on a change in pull request #2904:
URL: https://github.com/apache/couchdb/pull/2904#discussion_r458110597



##########
File path: src/couch_views/src/couch_views_http.erl
##########
@@ -143,21 +144,29 @@ do_paginated(PageSize, QueriesArgs, KeyFun, Fun) when is_list(QueriesArgs) ->
     lists:reverse(Results).
 
 
-maybe_add_bookmark(OriginalLimit, PageSize, Args0, Response, Items, KeyFun) ->
-    #mrargs{page_size = RequestedLimit} = Args0,
+maybe_add_next_bookmark(OriginalLimit, PageSize, Args0, Response, Items, KeyFun) ->
+    #mrargs{
+        page_size = RequestedLimit,
+        extra = Extra
+    } = Args0,
     case check_completion(OriginalLimit, RequestedLimit, Items) of
         {Rows, nil} ->
             maps:merge(Response, #{
                 rows => Rows,
                 total_rows => length(Rows)
             });
         {Rows, Next} ->
+            FirstKey = first_key(KeyFun, Rows),
             NextKey = KeyFun(Next),
             if is_binary(NextKey) -> ok; true ->
                 throw("Provided KeyFun should return binary")
             end,
-            Args = Args0#mrargs{page_size = PageSize},
-            Bookmark = bookmark_encode(Args#mrargs{start_key=NextKey}),
+            Args = Args0#mrargs{
+                page_size = PageSize,
+                start_key = NextKey,
+                extra = lists:keystore(fk, 1, Extra, {fk, FirstKey})
+            },
+            Bookmark = bookmark_encode(Args),

Review comment:
       With maps you can do:
   ```
   Response#{
      rows => Rows,
      next => BookMark
   }
   ```
   That is the same as using `maps:merge` and you can use it instead of doing a `maps:put` as well. But this depends on which style you prefer.




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