CouchDB: list of Erlang functions

Question

As I know, CouchDB allows to use some integrated Erlang functions like a sort (and something else).

Doing text trimming in JS again, I thought: what if Couch already built this feature in? Maybe trim also integrated? And how much functions are ready to use?

If they are already done in Erlang, why I must use slow JS-versions?

So, that's my question: where I can find full list of available from JS functions for Couch?

Conclusion: it only a few of functions available and there's no trim. You can test your luck by writing your own functions at couch_query_server.erl and then rebuilding Couch from source.

You want to know the list of Erlang functions (standard library) which can be used inside *CouchDB Erlang View*? If so, just take a look at their official documentation such as [string](http://www.erlang.org/doc/man/string.html) and so on. — Hamidreza Soleimani, Jan 11 '16 at 13:36
Not Erlang View, but JS views, handlers and anything at all. — Arman Hayots, Jan 11 '16 at 13:37

score 2 · Accepted Answer · edited May 23 '17 at 12:23

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CouchDB has three built-in reduce functions. These are implemented in Erlang and run right inside CouchDB, so they are much faster than the equivalent JavaScript functions.

They are _count, _sum and _stats. You can find more details and examples here. They are implemented in couch_query_server.erl file.

Also you can use built-in Erlang functions and features with writing Native Erlang Query Server. But notice that it is disabled by default.

An example from CouchDB documentation for implementing a native Erlang query server:

%% Map Function
fun({Doc}) ->
  <<K,_/binary>> = proplists:get_value(<<"_rev">>, Doc, null),
  V = proplists:get_value(<<"_id">>, Doc, null),
  Emit(<<K>>, V)
end.

%% Reduce Function
fun(Keys, Values, ReReduce) -> erlang:length(Values) end.

It uses proplists:get_value/3 and erlang:length/1 MFAs (Module Function Arity) which are in Erlang standard library.

Edit: This thread can be a possible duplicate which seems to be outdated.

edited May 23 '17 at 12:23

Community

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answered Jan 11 '16 at 13:48

Hamidreza Soleimani

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That's all? There's no more functions? – Arman Hayots Jan 11 '16 at 13:56
That's strange why so needed functions are not built-in for speed optimization. – Arman Hayots Jan 11 '16 at 13:56
Or maybe there's a way that I can define functions like that manually? – Arman Hayots Jan 11 '16 at 14:15
I'm talking about extending js by Erlang functions. E.g. defining `trim` function in Erlang and use from JS. – Arman Hayots Jan 11 '16 at 14:59
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@ArmanHayots I don't know if there is such solution in CouchDB, but projects like [erlang_js](https://github.com/basho/erlang_js) which is used inside [Riak](https://github.com/basho/riak_kv) might be interesting. – Hamidreza Soleimani Jan 11 '16 at 15:23
Another question about Couch, you're welcome. http://stackoverflow.com/questions/34725149 – Arman Hayots Jan 11 '16 at 15:27

CouchDB: list of Erlang functions

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