Update documentation.

[dead/htsn-import.git] / src / TSN / DbImport.hs

diff --git a/src/TSN/DbImport.hs b/src/TSN/DbImport.hs
index 8884a9eef4708597aaca4b2ac22b6d5530f7391c..62cc8a10032eac904742f48d312454001b731209 100644 (file)
--- a/src/TSN/DbImport.hs
+++ b/src/TSN/DbImport.hs
@@ -1,4 +1,21 @@
 -- | Definition of the DbImport typeclass.
+--
+--   When we parse an XML tree, there are two functions that we would
+--   like to call on the result independent of its type. First, we
+--   would like to be able to run the database migrations for that
+--   type. The migrations are kept separate from insertion because, at
+--   some later point, it make make sense to disable automatic
+--   migrations.
+--
+--   Next we want to import the thing.
+--
+--   Neither of these should depend on the type -- we should just be
+--   able to call 'dbmigrate' followed by 'dbimport' on the
+--   datastructure and have the right thing happen. That is the
+--   purpose of the 'DbImport' typeclass. It allows the XML types to
+--   define their own \"migrate me\" and \"insert me\" functions that
+--   the rest of the application doesn't have to care about.
+--
 module TSN.DbImport (
   DbImport(..),
   ImportResult(..),
@@ -31,20 +48,20 @@ data ImportResult =
                              --   The second field should contain info.
 
 
--- | Instances of this type know how to insert themselves into a
---   Groundhog database.
+-- | Instances of this type know how to run their own database
+--   migrations and insert themselves into a database.
 --
 class DbImport a where
   -- | Import an instance of type @a@.
   dbimport :: (PersistBackend m) => a -> m ImportResult
 
   -- | This must migrate *all* stuffs that can potentially be
-  -- created/used by the type @a@.
+  --   created/used by the type @a@.
   dbmigrate :: (MonadIO m, PersistBackend m) => a -> m ()
 
 
 -- | The simplest possible implementation of 'dbimport', for types
---   which happen to be members of the XmlImport typeclass.
+--   which happen to be members of the 'XmlImport' typeclass.
 --
 dbimport_generic :: (XmlImport a, MonadIO m, PersistBackend m)
                  => a
@@ -54,6 +71,7 @@ dbimport_generic x = insert_xml x >> return ImportSucceeded
 
 -- | A migration runner that will use our normal info reporting
 --   mechanism.
+--
 run_dbmigrate :: (MonadIO m, PersistBackend m) => Migration m -> m ()
 run_dbmigrate =
   runMigration pretty_migration_logger