From 7cfabb5543de52639d226f509897e9b418327fcb Mon Sep 17 00:00:00 2001
From: Nick Vatamaniuc <vatamane@gmail.com>
Date: Thu, 2 Jun 2016 17:16:33 -0400
Subject: [PATCH] Add optional `fields` to change feed selectors

When using selectors with `include_docs=true` can specify an optional fields
array in the POST request JSON body.

Each element in the array can be a json field (or even a key path
specified as field1.field2...). Resulting documents will contain only the
specified document fields.

For example:
```
http://.../d1/_changes?filter=_selector&include_docs=true

{
    "selector": {"z" : {"$gte" : 1} }, "fields": ["field1", "field2"]
}
```
Will first select only document with "z" value >= 1, then will return only field1 and field2 in documents.

```{ "field1": "field1value", "field2": "field2value"}```

(This is a companion pr. Main pr is in couch repo)

Jira: COUCHDB-2988
---
 src/fabric_rpc.erl | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/src/fabric_rpc.erl b/src/fabric_rpc.erl
index afe7490..3a21d83 100644
--- a/src/fabric_rpc.erl
+++ b/src/fabric_rpc.erl
@@ -352,20 +352,27 @@ changes_enumerator(DocInfo, Acc) ->
             {id, Id},
             {changes, Results},
             {deleted, Del} |
-            if IncludeDocs -> [doc_member(Db, DocInfo, Opts)]; true -> [] end
+            if IncludeDocs -> [doc_member(Db, DocInfo, Opts, Filter)]; true -> [] end
         ]}
     end,
     ok = rexi:stream2(ChangesRow),
     {ok, Acc#cacc{seq = Seq, pending = Pending-1}}.
 
-doc_member(Shard, DocInfo, Opts) ->
+doc_member(Shard, DocInfo, Opts, Filter) ->
     case couch_db:open_doc(Shard, DocInfo, [deleted | Opts]) of
     {ok, Doc} ->
-        {doc, couch_doc:to_json_obj(Doc, Opts)};
+        {doc, maybe_filtered_json_doc(Doc, Opts, Filter)};
     Error ->
         Error
     end.
 
+maybe_filtered_json_doc(Doc, Opts, {selector, _Style, {_Selector, Fields}})
+    when Fields =/= nil ->
+    mango_fields:extract(couch_doc:to_json_obj(Doc, Opts), Fields);
+maybe_filtered_json_doc(Doc, Opts, _Filter) ->
+    couch_doc:to_json_obj(Doc, Opts).
+
+
 possible_ancestors(_FullInfo, []) ->
     [];
 possible_ancestors(FullInfo, MissingRevs) ->
@@ -546,4 +553,19 @@ is_owner_test() ->
     ?assertError(duplicate_epoch, is_owner(foo, 1, [{foo, 1}, {bar, 1}])),
     ?assertError(epoch_order, is_owner(foo, 1, [{foo, 100}, {bar, 200}])).
 
+maybe_filtered_json_doc_no_filter_test() ->
+    Body = {[{<<"a">>, 1}]},
+    Doc = #doc{id = <<"1">>, revs = {1, [<<"r1">>]}, body = Body},
+    {JDocProps} = maybe_filtered_json_doc(Doc, [], x),
+    ExpectedProps = [{<<"_id">>, <<"1">>}, {<<"_rev">>, <<"1-r1">>}, {<<"a">>, 1}],
+    ?assertEqual(lists:keysort(1, JDocProps), ExpectedProps).
+
+maybe_filtered_json_doc_with_filter_test() ->
+    Body = {[{<<"a">>, 1}]},
+    Doc = #doc{id = <<"1">>, revs = {1, [<<"r1">>]}, body = Body},
+    Fields = [<<"a">>, <<"nonexistent">>],
+    Filter = {selector, main_only, {some_selector, Fields}},
+    {JDocProps} = maybe_filtered_json_doc(Doc, [], Filter),
+    ?assertEqual(JDocProps, [{<<"a">>, 1}]).
+
 -endif.