Add lookup/2 to the specific types

They proxy to geef_object:lookup/3 which looks up the object and
asserts the type.

src/geef_object.erl

@@ -6,19 +6,29 @@
 
 -include("geef_records.hrl").
 
--export([lookup/2, id/1]).
+-export([lookup/2, lookup/3, id/1]).
 
--spec lookup(pid(), oid() | iolist()) -> object().
+-spec lookup(pid(), oid() | iolist()) -> {ok, object()} | {error, term()}.
 lookup(Repo, #oid{oid=Oid}) ->
     case geef_repo:lookup_object(Repo, Oid) of
 	{ok, Type, Handle} ->
 	    {ok, #object{type=Type, handle=Handle}};
-	Other ->
-	    Other
+	{error, Err} ->
+	    {error, Err}
     end;
 lookup(Repo, Id) ->
     lookup(Repo, geef_oid:parse(Id)).
 
+%% As lookup/2, but it asserts that the type is correct
+-spec lookup(pid(), oid() | iolist(), atom()) -> {ok, object()} | {error, term()}.
+lookup(Repo, Id, Type) ->
+    case lookup(Repo, Id) of
+	{ok, Obj = #object{type=Type}} ->
+	    {ok, Obj};
+	{error, Err} ->
+	    {error, Err}
+    end.
+
 id(#object{handle=Handle}) ->
     case geef:object_id(Handle) of
 	{ok, Oid} ->