3.3. Erlang

The Erlang query server is disabled by default. Read configuration guide about reasons why and how to enable it.

(Id, Value)

Emits key-value pairs to view indexer process.

FoldRows(Fun, Acc)

Helper to iterate over all rows in a list function.

• • Fun – Function object.

  • Acc – The value previously returned by Fun.

fun(Head, {Req}) ->
    Fun = fun({Row}, Acc) ->
        Id = couch_util:get_value(<<"id">>, Row),
        Send(list_to_binary(io_lib:format("Previous doc id: ~p~n", [Acc]))),
        Send(list_to_binary(io_lib:format("Current  doc id: ~p~n", [Id]))),
        {ok, Id}
    end,
    FoldRows(Fun, nil),
end.

()

Retrieves the next row from a related view result.

Log(Msg)

• • Msg – Log a message at the INFO level.

fun({Doc}) ->
    <<K,_/binary>> = proplists:get_value(<<"_rev">>, Doc, null),
    V = proplists:get_value(<<"_id">>, Doc, null),
    Log(lists:flatten(io_lib:format("Hello from ~s doc!", [V]))),
    Emit(<<K>>, V)
end.

After the map function has run, the following line can be found in CouchDB logs (e.g. at /var/log/couchdb/couch.log):

Send(Chunk)

Sends a single string Chunk in response.

fun(Head, {Req}) ->
    Send("Hello,"),
    "!"
end.

The function above produces the following response:

Start(Headers)

• • Headers – Proplist of .

Initialize List Functions response. At this point, response code and headers may be defined. For example, this function redirects to the CouchDB web site:

fun(Head, {Req}) ->
    Start({[{<<"code">>, 302},
            {<<"headers">>, {[
                {<<"Location">>, <<"http://couchdb.apache.org">>}]
            }}
        ]}),
end.