mikerhodes commented on code in PR #4394:
URL: https://github.com/apache/couchdb/pull/4394#discussion_r1081539012
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src/mango/src/mango_cursor_view.erl:
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@@ -248,6 +266,19 @@ view_cb({row, Row}, #mrargs{extra = Options} = Acc) ->
key = couch_util:get_value(key, Row),
doc = couch_util:get_value(doc, Row)
},
+ % This supports receiving our "arguments" either as just the `selector`
+ % or in the new record in `callback_args`. This is to support mid-upgrade
+ % clusters where the non-upgraded coordinator nodes will send the older
style.
+ % TODO remove this in a couple of couchdb versions.
+ {Selector, Fields} =
+ case couch_util:get_value(callback_args, Options) of
+ % old style
+ undefined ->
+ {couch_util:get_value(selector, Options), undefined};
+ % new style - assume a viewcbargs
+ Args ->
Review Comment:
I wanted to avoid exposing the "internals" of the viewcbargs here. I found
you couldn't use your own function in a guard only a BIF, ie, I tried `when
is_viewcbargs(Args)`. In the end, perhaps you're right that it's better to leak
the Map implementation such that there is a decent guard on the `case`
statement -- what do you think, I'm not sure what works well in Erlang here?
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