From c596db1079f5a062a89c4c70dbb1e2929f7b0d84 Mon Sep 17 00:00:00 2001
From: John Christopher Anderson <jchris@apache.org>
Date: Tue, 12 May 2009 21:38:43 +0000
Subject: You can now specify either "_sum" or "_count" as the source code for
 2 built-in Erlang reduce functions. The framework is ready for YOU to add
 more built in reductions. The short list includes: _avg, _stddev, _min, and
 _max. We could also have one function that does all that in a single
 function, but it might not be as fun to use.

git-svn-id: https://svn.apache.org/repos/asf/couchdb/trunk@774101 13f79535-47bb-0310-9956-ffa450edef68
---
 src/couchdb/couch_query_servers.erl | 52 +++++++++++++++++++++++++++++++++----
 1 file changed, 47 insertions(+), 5 deletions(-)

(limited to 'src/couchdb/couch_query_servers.erl')

diff --git a/src/couchdb/couch_query_servers.erl b/src/couchdb/couch_query_servers.erl
index a27943a1..734baade 100644
--- a/src/couchdb/couch_query_servers.erl
+++ b/src/couchdb/couch_query_servers.erl
@@ -86,7 +86,11 @@ rereduce(Lang, RedSrcs, ReducedValues) ->
     Pid = get_os_process(Lang),
     Grouped = group_reductions_results(ReducedValues),
     Results = try lists:zipwith(
-        fun(FunSrc, Values) ->
+        fun
+        (<<"_", _/binary>> = FunSrc, Values) ->
+            {ok, [Result]} = builtin_reduce(rereduce, [FunSrc], [[[], V] || V <- Values], []),
+            Result;
+        (FunSrc, Values) ->
             [true, [Result]] = 
                 couch_os_process:prompt(Pid, [<<"rereduce">>, [FunSrc], Values]),
             Result
@@ -99,15 +103,53 @@ rereduce(Lang, RedSrcs, ReducedValues) ->
 reduce(_Lang, [], _KVs) ->
     {ok, []};
 reduce(Lang, RedSrcs, KVs) ->
+    {OsRedSrcs, BuiltinReds} = lists:partition(fun
+        (<<"_", _/binary>>) -> false;
+        (_OsFun) -> true
+    end, RedSrcs),
+    {ok, OsResults} = os_reduce(Lang, OsRedSrcs, KVs),
+    {ok, BuiltinResults} = builtin_reduce(reduce, BuiltinReds, KVs, []),
+    recombine_reduce_results(RedSrcs, OsResults, BuiltinResults, []).
+
+recombine_reduce_results([], [], [], Acc) ->
+    {ok, lists:reverse(Acc)};
+recombine_reduce_results([<<"_", _/binary>>|RedSrcs], OsResults, [BRes|BuiltinResults], Acc) ->
+    recombine_reduce_results(RedSrcs, OsResults, BuiltinResults, [BRes|Acc]);
+recombine_reduce_results([_OsFun|RedSrcs], [OsR|OsResults], BuiltinResults, Acc) ->
+    recombine_reduce_results(RedSrcs, OsResults, BuiltinResults, [OsR|Acc]).
+
+os_reduce(Lang, [], KVs) ->
+    {ok, []};
+os_reduce(Lang, OsRedSrcs, KVs) ->
     Pid = get_os_process(Lang),
-    Results = try couch_os_process:prompt(Pid, 
-            [<<"reduce">>, RedSrcs, KVs]) of
+    OsResults = try couch_os_process:prompt(Pid, 
+            [<<"reduce">>, OsRedSrcs, KVs]) of
         [true, Reductions] -> Reductions
     after
         ok = ret_os_process(Lang, Pid)
     end,
-    {ok, Results}.
-
+    {ok, OsResults}.
+
+builtin_reduce(_Re, [], KVs, Acc) ->
+    {ok, lists:reverse(Acc)};
+builtin_reduce(Re, [<<"_sum">>|BuiltinReds], KVs, Acc) ->
+    Sum = builtin_sum_rows(KVs),
+    builtin_reduce(Re, BuiltinReds, KVs, [Sum|Acc]);
+builtin_reduce(reduce, [<<"_count">>|BuiltinReds], KVs, Acc) ->
+    Count = length(KVs),
+    builtin_reduce(reduce, BuiltinReds, KVs, [Count|Acc]);
+builtin_reduce(rereduce, [<<"_count">>|BuiltinReds], KVs, Acc) ->
+    Count = builtin_sum_rows(KVs),
+    builtin_reduce(rereduce, BuiltinReds, KVs, [Count|Acc]).
+
+builtin_sum_rows(KVs) ->
+    lists:foldl(fun
+        ([_Key, Value], Acc) when is_number(Value) -> 
+            Acc + Value;
+        (_Else, _Acc) -> 
+            throw({invalid_value, <<"builtin _sum function requires map values to be numbers">>})
+    end, 0, KVs).
+    
 validate_doc_update(Lang, FunSrc, EditDoc, DiskDoc, Ctx) ->
     Pid = get_os_process(Lang),
     JsonEditDoc = couch_doc:to_json_obj(EditDoc, [revs]),
-- 
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