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72 lines
2.2 KiB
Haskell
72 lines
2.2 KiB
Haskell
{- This file is part of Vervis.
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-
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- Written in 2016 by fr33domlover <fr33domlover@riseup.net>.
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-
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- ♡ Copying is an act of love. Please copy, reuse and share.
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-
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- The author(s) have dedicated all copyright and related and neighboring
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- rights to this software to the public domain worldwide. This software is
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- distributed without any warranty.
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-
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- You should have received a copy of the CC0 Public Domain Dedication along
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- with this software. If not, see
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- <http://creativecommons.org/publicdomain/zero/1.0/>.
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-}
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module Vervis.Migration
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( migrateDB
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)
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where
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import Prelude
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import Control.Monad.IO.Class (MonadIO)
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import Control.Monad.Trans.Reader (ReaderT, runReaderT)
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import Data.Maybe (fromMaybe)
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import Database.Persist
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import Database.Persist.Sql (SqlBackend, toSqlKey)
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import Database.Persist.Schema
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import Database.Persist.Schema.PostgreSQL (schemaBackend)
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import Vervis.Model
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key :: SchemaVersionId
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key = toSqlKey 1
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getDbSchemaVersion :: MonadIO m => ReaderT SqlBackend m (Maybe Int)
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getDbSchemaVersion = fmap schemaVersionNumber <$> get key
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setDbSchemaVersion :: MonadIO m => Int -> ReaderT SqlBackend m ()
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setDbSchemaVersion v = update key [SchemaVersionNumber =. v]
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-- | Run the migration system. The second parameter is the list of migration
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-- actions in chronological order. The migration process is:
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--
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-- * Check the schema version of the DB
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-- * Compare to the schema version of the app, which is the length of the list
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-- * If any migrations are required, run them
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-- * Update the schema version in the DB
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runMigrations
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:: MonadIO m
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=> SchemaBackend SqlBackend
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-> [SchemaT SqlBackend m ()]
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-> ReaderT SqlBackend m ()
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runMigrations sb migrations = do
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dver <- fromMaybe 0 <$> getDbSchemaVersion
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let aver = length migrations
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case compare aver dver of
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LT -> error "Older app version running with newer DB schema version"
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EQ -> return ()
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GT -> do
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let migs = drop dver migrations
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runReaderT (sequence migs) sb
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setDbSchemaVersion aver
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changes :: MonadIO m => [SchemaT SqlBackend m ()]
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changes =
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[
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]
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migrateDB :: MonadIO m => ReaderT SqlBackend m ()
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migrateDB = runMigrations schemaBackend changes
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