Emit Tuples From Erlang Views In CouchDB - erlang

Question

CouchDB, version 0.10.0, using native erlang views.
I have a simple document of the form:
{
"_id": "user-1",
"_rev": "1-9ccf63b66b62d15d75daa211c5a7fb0d",
"type": "user",
"identifiers": [
"ABC",
"DEF",
"123"
],
"username": "monkey",
"name": "Monkey Man"
}
And a basic javascript design document:
{
"_id": "_design/user",
"_rev": "1-94bd8a0dbce5e2efd699d17acea1db0b",
"language": "javascript",
"views": {
"find_by_identifier": {
"map": "function(doc) {
if (doc.type == 'user') {
doc.identifiers.forEach(function(identifier) {
emit(identifier, {\"username\":doc.username,\"name\":doc.name});
});
}
}"
}
}
}
which emits:
{"total_rows":3,"offset":0,"rows":[
{"id":"user-1","key":"ABC","value":{"username":"monkey","name":"Monkey Man"}},
{"id":"user-1","key":"DEF","value":{"username":"monkey","name":"Monkey Man"}},
{"id":"user-1","key":"123","value":{"username":"monkey","name":"Monkey Man"}}
]}
I'm looking into building an Erlang view that does the same thing. Best attempt so far is:
%% Map Function
fun({Doc}) ->
case proplists:get_value(<<"type">>, Doc) of
undefined ->
ok;
Type ->
Identifiers = proplists:get_value(<<"identifiers">>, Doc),
ID = proplists:get_value(<<"_id">>, Doc),
Username = proplists:get_value(<<"username">>, Doc),
Name = proplists:get_value(<<"name">>, Doc),
lists:foreach(fun(Identifier) -> Emit(Identifier, [ID, Username, Name]) end, Identifiers);
_ ->
ok
end
end.
which emits:
{"total_rows":3,"offset":0,"rows":[
{"id":"user-1","key":"ABC","value":["monkey","Monkey Man"]},
{"id":"user-1","key":"DEF","value":["monkey","Monkey Man"]},
{"id":"user-1","key":"123","value":["monkey","Monkey Man"]}
]}
The question is - how can I get those values out as tuples, instead of as arrays? I don't imagine I can (or would want to) use records, but using atoms in a tuple doesn't seem to work.
lists:foreach(fun(Identifier) -> Emit(Identifier, {id, ID, username, Username, name, Name}) end, Identifiers);
Fails with the following error:
{"error":"json_encode","reason":"{bad_term,{<<\"user-1\">>,<<\"monkey\">>,<<\"Monkey Man\">>}}"}
Thoughts? I know that Erlang sucks for this specific kind of thing (named access) and that I can do it by convention (id at first position, username next, real name last), but that makes the client side code pretty ugly.

Answer 1

The JSON object {"foo":"bar","baz":1} is {[{<<"foo">>,<<"bar">>},{<<"baz">>,1}]}
In Erlang lingua it is a proplist wrapped in a tuple.
It's not pretty, but very efficient :)
To get a feel for it you can play with the JSON lib that ships with CouchDB:
Start CouchDB with the -i
(interactive) flag
On the resulting erlang shell, type: couch_util:json_decode(<<"{\"foo\":\"bar\"}">>).
Profit
// in later versions of CouchDB, this is ejson:decode()

Answer 2

For test_suite_reports bd, that has tests field:
[
{
"name": "basics",
"status": "success",
"duration": 21795
},
{
"name": "all_docs",
"status": "success",
"duration": 385
} ...
I have wrote this to get name and status:
fun({Doc}) ->
Name = fun(L) -> proplists:get_value(<<"name">>, L, null) end,
Status = fun(L) -> proplists:get_value(<<"status">>, L, null) end,
Tests = proplists:get_value(<<"tests">>, Doc, null),
lists:foreach(fun({L}) -> Emit(Name(L), Status(L)) end, Tests)
end.

Answer 3

If you like experimental features (that still work...), you might want to have a look to Erlang exprecs.
I found it extremely helpful in creating a sort of dynamic records for Erlang.