diff --git a/hmemdb.cabal b/hmemdb.cabal
--- a/hmemdb.cabal
+++ b/hmemdb.cabal
@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                hmemdb
-version:             0.1.0.5
+version:             0.2.0.0
 synopsis:            In-memory relational database
 description:         Library that provides a sort of relational database in memory (which could be saved to the disk, however). Very untested.
 license:             BSD3
@@ -16,18 +16,19 @@
 
 library
   exposed-modules:     Data.HMemDb
-  other-modules:       Data.HMemDb.Utils,
-                       Data.HMemDb.TableVars,
-                       Data.HMemDb.Tables,
-                       Data.HMemDb.Specs, 
-                       Data.HMemDb.References, 
-                       Data.HMemDb.RefConverter, 
-                       Data.HMemDb.RefContainer, 
-                       Data.HMemDb.Persistence,
-                       Data.HMemDb.KeyBackends,
-                       Data.HMemDb.ForeignKeys,
-                       Data.HMemDb.CreateTable, 
+  other-modules:       Data.HMemDb.Bin,
                        Data.HMemDb.Binary,
-                       Data.HMemDb.Bin
+                       Data.HMemDb.CreateTable, 
+                       Data.HMemDb.ForeignKeys,
+                       Data.HMemDb.KeyBackends,
+                       Data.HMemDb.Persistence,
+                       Data.HMemDb.RefContainer, 
+                       Data.HMemDb.RefConverter, 
+                       Data.HMemDb.References, 
+                       Data.HMemDb.Specs, 
+                       Data.HMemDb.Tables,
+                       Data.HMemDb.TableVarId,
+                       Data.HMemDb.TableVars,
+                       Data.HMemDb.Utils
   build-depends:       base ==4.6.*, TypeCompose ==0.9.*, transformers ==0.3.*, stm ==2.4.*, containers ==0.5.*, binary ==0.5.*
   hs-source-dirs:      src
diff --git a/src/Data/HMemDb/TableVarId.hs b/src/Data/HMemDb/TableVarId.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/HMemDb/TableVarId.hs
@@ -0,0 +1,45 @@
+module Data.HMemDb.TableVarId (TableVarId, idToVar, tableIds, tvIdTarget, varToId) where
+import Control.Compose (Id(Id), unId)
+import Control.Concurrent.STM (readTVar)
+import Control.Monad.Trans.Class (lift)
+import Data.Function (on)
+import qualified Data.Map as M (lookup)
+import Data.HMemDb.Binary (MS)
+import Data.HMemDb.ForeignKeys (ForeignKey(ForeignKey))
+import Data.HMemDb.References (Ref(Ref, refContent, refIndex))
+import Data.HMemDb.Tables (Table(Table), tabContent)
+import Data.HMemDb.TableVars (TableVar, TableVarS(TableVar))
+import Data.HMemDb.Utils (liftMaybe)
+data TableVarId a =
+    TableVarId
+    {
+      unTVId :: Integer,
+      tvIdTarget :: Table a -- ^ 'Table' this id points to.
+    }
+-- ^ This type can be used for columns in a table.
+-- It's sort of a 'ForeignKey' accompanied with a specific index.
+instance Eq (TableVarId a) where (==) = (==) `on` unTVId
+-- ^ 'TableVarId's pointing to different 'Table's may accidentally appear equal.
+instance Ord (TableVarId a) where compare = compare `on` unTVId
+varToId :: TableVar a -> TableVarId a
+-- ^ This function gets an Id of the variable.
+varToId (TableVar iref pt) =
+    TableVarId {unTVId = refIndex (unId iref), tvIdTarget = Table pt}
+idToVar :: TableVarId a -> MS (TableVar a)
+-- ^ This function looks up the specific Id in the 'Table'.
+idToVar tvId =
+    case tvIdTarget tvId of
+      Table pt ->
+          do mp <- lift $ readTVar $ tabContent pt
+             let i = unTVId tvId
+             tv <- liftMaybe $ M.lookup i mp
+             return $ TableVar (Id Ref {refContent = tv, refIndex = i}) pt
+tableIds :: Table a -> ForeignKey Id (TableVarId a) a
+-- ^ If you want to use 'TableVarId' as a column type in a table,
+-- you'd need a 'ForeignKey'. This function provides one.
+tableIds (Table pt) =
+    ForeignKey pt $ \tvId -> do
+      mp <- lift (readTVar $ tabContent pt)
+      let i = unTVId tvId
+      tv <- liftMaybe $ M.lookup i mp
+      return $ Id Ref {refContent = tv, refIndex = i}