diff --git a/src/Database/Persist/Local/Class/PersistEntityGraph.hs b/src/Database/Persist/Local/Class/PersistEntityGraph.hs
index 6f4bd81..cf4e6dd 100644
--- a/src/Database/Persist/Local/Class/PersistEntityGraph.hs
+++ b/src/Database/Persist/Local/Class/PersistEntityGraph.hs
@@ -15,6 +15,8 @@
 
 module Database.Persist.Local.Class.PersistEntityGraph
     ( PersistEntityGraph (..)
+    , PersistEntityGraphSelect (..)
+    , PersistEntityGraphNumbered (..)
     )
 where
 
@@ -23,8 +25,17 @@ import Prelude
 import Database.Persist
 
 class (PersistEntity n, PersistEntity e) => PersistEntityGraph n e where
+    sourceParam   :: e -> Key n
+    sourceField   :: EntityField e (Key n)
+    destParam     :: e -> Key n
+    destField     :: EntityField e (Key n)
+
+class PersistEntityGraph n e => PersistEntityGraphSelect n e where
     type PersistEntityGraphSelector n e
-    sourceParam :: e -> Key n
-    sourceField :: EntityField e (Key n)
-    destParam   :: e -> Key n
-    destField   :: EntityField e (Key n)
+    selectorParam :: n -> PersistEntityGraphSelector n e
+    selectorField :: EntityField n (PersistEntityGraphSelector n e)
+
+class PersistEntityGraphSelect n e => PersistEntityGraphNumbered n e where
+    numberParam :: n -> Int
+    numberField :: EntityField n Int
+    uniqueNode  :: PersistEntityGraphSelector n e -> Int -> Unique n
diff --git a/src/Vervis/Model.hs b/src/Vervis/Model.hs
index 63467f0..ccab504 100644
--- a/src/Vervis/Model.hs
+++ b/src/Vervis/Model.hs
@@ -56,8 +56,17 @@ instance Hashable ProjectRoleId where
     hash = hash . fromSqlKey
 
 instance PersistEntityGraph Ticket TicketDependency where
-    type PersistEntityGraphSelector Ticket TicketDependency = ProjectId
     sourceParam = ticketDependencyParent
     sourceField = TicketDependencyParent
     destParam   = ticketDependencyChild
     destField   = TicketDependencyChild
+
+instance PersistEntityGraphSelect Ticket TicketDependency where
+    type PersistEntityGraphSelector Ticket TicketDependency = ProjectId
+    selectorParam = ticketProject
+    selectorField = TicketProject
+
+instance PersistEntityGraphNumbered Ticket TicketDependency where
+    numberParam = ticketNumber
+    numberField = TicketNumber
+    uniqueNode  = UniqueTicket