-- | Definition of the DbImport typeclass.
-module TSN.DbImport
+--
+-- 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(..),
+ run_dbmigrate )
where
-import Control.Monad.IO.Class ( MonadIO, liftIO )
-import Database.Groundhog (
- defaultMigrationLogger,
- insert,
- migrate,
- runMigration )
-import Database.Groundhog.Core ( PersistBackend, PersistEntity )
-import Network.Services.TSN.Report ( report_error )
-import Text.XML.HXT.Core (
- XmlPickler,
- XmlTree,
- unpickleDoc,
- xpickle )
-
--- | Instances of this type know how to insert themselves into a
--- Groundhog database.
+-- System imports
+import Control.Monad.IO.Class ( MonadIO )
+import Database.Groundhog ( runMigration )
+import Database.Groundhog.Core ( Migration, PersistBackend )
+import Network.Services.TSN.Report ( report_info )
+
+
+-- | The type that will be returned from every file import attempt.
+--
+data ImportResult =
+ ImportFailed String -- ^ Failure with an error message.
+
+ | ImportSkipped String -- ^ We processed the file, but didn't import it.
+ -- The reason is contained in the second field.
+
+ | ImportSucceeded -- ^ We did import records.
+
+ | ImportUnsupported String -- ^ We didn't know how to process this file.
+ -- The second field should contain info.
+
+
+-- | Instances of this type know how to run their own database
+-- migrations and insert themselves into a database.
+--
class DbImport a where
- dbimport :: (MonadIO m, PersistBackend m)
- => a
- -> XmlTree
- -> m (Maybe Int)
+ -- | 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@.
+ dbmigrate :: (MonadIO m, PersistBackend m) => a -> m ()
--- | We put the 'Configuration' and 'XmlTree' arguments last so that
--- it's easy to eta reduce all of the import_foo functions that call
--- this.
+-- | A migration runner that will use our normal info reporting
+-- mechanism.
--
-import_generic :: (XmlPickler a, MonadIO m, PersistEntity b, PersistBackend m)
- => (a -> [b]) -- ^ listings getter
- -> b -- ^ Dummy Listing instance needed for 'migrate'
- -> XmlTree
- -> m (Maybe Int) -- ^ Return the number of records inserted.
-import_generic g dummy xml = do
- runMigration defaultMigrationLogger $ migrate dummy
- let root_element = unpickleDoc xpickle xml
- case root_element of
- Nothing -> do
- let msg = "Could not unpickle document in import_generic."
- liftIO $ report_error msg
- return Nothing
- Just elt -> do
- ids <- mapM insert (g elt)
- return $ Just (length ids)
+run_dbmigrate :: (MonadIO m, PersistBackend m) => Migration m -> m ()
+run_dbmigrate =
+ runMigration pretty_migration_logger
+ where
+ pretty_migration_logger x =
+ report_info ("Migration: " ++ x ++ ";")