3.3. Erlang¶
Note
The Erlang query server is disabled by default. Read configuration guide about reasons why and how to enable it.
- Emit(Id, Value)¶
Emits key-value pairs to view indexer process.
fun({Doc}) -> <<K,_/binary>> = proplists:get_value(<<"_rev">>, Doc, null), V = proplists:get_value(<<"_id">>, Doc, null), Emit(<<K>>, V) end.
- FoldRows(Fun, Acc)¶
Helper to iterate over all rows in a list function.
- Arguments:
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.
- GetRow()¶
Retrieves the next row from a related view result.
%% FoldRows background implementation. %% https://git-wip-us.apache.org/repos/asf?p=couchdb.git;a=blob;f=src/couchdb/couch_native_process.erl;hb=HEAD#l368 %% foldrows(GetRow, ProcRow, Acc) -> case GetRow() of nil -> {ok, Acc}; Row -> case (catch ProcRow(Row, Acc)) of {ok, Acc2} -> foldrows(GetRow, ProcRow, Acc2); {stop, Acc2} -> {ok, Acc2} end end.
- Log(Msg)¶
- Arguments:
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):
[Sun, 04 Nov 2012 11:33:58 GMT] [info] [<0.9144.2>] Hello from 8d300b86622d67953d102165dbe99467 doc!
- Send(Chunk)¶
Sends a single string Chunk in response.
fun(Head, {Req}) -> Send("Hello,"), Send(" "), Send("Couch"), "!" end.
The function above produces the following response:
Hello, Couch!
- Start(Headers)¶
- Arguments:
Headers – Proplist of response object.
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">>}] }} ]}), "Relax!" end.