-- |
-- Module : Database.PostgreSQL.Simple.Migration
-- Copyright : (c) 2014 Andreas Meingast <ameingast@gmail.com>
--
-- License : BSD-style
-- Maintainer : ameingast@gmail.com
-- Stability : experimental
-- Portability : GHC
--
-- A migration library for postgresql-simple.
--
-- For usage, see Readme.markdown.
module Database.PostgreSQL.Simple.Migration
(
-- * Migration actions
runMigration
-- * Migration types
, MigrationContext(..)
, MigrationCommand(..)
, MigrationResult(..)
, ScriptName
, Checksum
-- * Migration result actions
, getMigrations
-- * Migration result types
, SchemaMigration(..)
) where
import Control.Applicative ((<$>), (<*>))
import Control.Monad (liftM, void, when)
import qualified Crypto.Hash.MD5 as MD5 (hash)
import qualified Data.ByteString as BS (ByteString, readFile)
import qualified Data.ByteString.Base64 as B64 (encode)
import Data.List (isPrefixOf, sort)
import Data.Monoid (mconcat)
import Data.Time (LocalTime)
import Database.PostgreSQL.Simple (Connection, Only (..),
execute, execute_, query,
query_)
import Database.PostgreSQL.Simple.FromRow (FromRow (..), field)
import Database.PostgreSQL.Simple.ToField (ToField (..))
import Database.PostgreSQL.Simple.ToRow (ToRow (..))
import Database.PostgreSQL.Simple.Types (Query (..))
import Database.PostgreSQL.Simple.Util (existsTable)
import System.Directory (getDirectoryContents)
-- | Executes migrations inside the provided 'MigrationContext'.
--
-- Returns 'MigrationSuccess' if the provided 'MigrationCommand' executes
-- without error. If an error occurs, execution is stopped and
-- a 'MigrationError' is returned.
--
-- It is recommended to wrap 'runMigration' inside a database transaction.
runMigration :: MigrationContext -> IO (MigrationResult String)
runMigration (MigrationContext cmd verbose con) = case cmd of
MigrationInitialization ->
initializeSchema con verbose >> return MigrationSuccess
MigrationDirectory path ->
executeDirectoryMigration con verbose path
MigrationScript name contents ->
executeMigration con verbose name contents
MigrationFile name path ->
executeMigration con verbose name =<< BS.readFile path
MigrationValidation validationCmd ->
executeValidation con verbose validationCmd
-- | Executes all SQL-file based migrations located in the provided 'dir'
-- in alphabetical order.
executeDirectoryMigration :: Connection -> Bool -> FilePath -> IO (MigrationResult String)
executeDirectoryMigration con verbose dir =
scriptsInDirectory dir >>= go
where
go [] = return MigrationSuccess
go (f:fs) = do
r <- executeMigration con verbose f =<< BS.readFile (dir ++ "/" ++ f)
case r of
MigrationError _ ->
return r
MigrationSuccess ->
go fs
-- | Lists all files in the given 'FilePath' 'dir' in alphabetical order.
scriptsInDirectory :: FilePath -> IO [String]
scriptsInDirectory dir =
liftM (sort . filter (\x -> not $ "." `isPrefixOf` x))
(getDirectoryContents dir)
-- | Executes a generic SQL migration for the provided script 'name' with
-- content 'contents'.
executeMigration :: Connection -> Bool -> ScriptName -> BS.ByteString -> IO (MigrationResult String)
executeMigration con verbose name contents = do
let checksum = md5Hash contents
checkScript con name checksum >>= \r -> case r of
ScriptOk -> do
when verbose $ putStrLn $ "Ok:\t" ++ name
return MigrationSuccess
ScriptNotExecuted -> do
void $ execute_ con (Query contents)
void $ execute con q (name, checksum)
when verbose $ putStrLn $ "Execute:\t" ++ name
return MigrationSuccess
ScriptModified _ -> do
when verbose $ putStrLn $ "Fail:\t" ++ name
return (MigrationError name)
where
q = "insert into schema_migrations(filename, checksum) values(?, ?)"
-- | Initializes the database schema with a helper table containing
-- meta-information about executed migrations.
initializeSchema :: Connection -> Bool -> IO ()
initializeSchema con verbose = do
when verbose $ putStrLn "Initializing schema"
void $ execute_ con $ mconcat
[ "create table if not exists schema_migrations "
, "( filename varchar(512) not null"
, ", checksum varchar(32) not null"
, ", executed_at timestamp without time zone not null default now() "
, ");"
]
-- | Validates a 'MigrationCommand'. Validation is defined as follows for these
-- types:
--
-- * 'MigrationInitialization': validate the presence of the meta-information
-- table.
-- * 'MigrationDirectory': validate the presence and checksum of all scripts
-- found in the given directory.
-- * 'MigrationScript': validate the presence and checksum of the given script.
-- * 'MigrationFile': validate the presence and checksum of the given file.
-- * 'MigrationValidation': always succeeds.
executeValidation :: Connection -> Bool -> MigrationCommand -> IO (MigrationResult String)
executeValidation con verbose cmd = case cmd of
MigrationInitialization ->
existsTable con "schema_migrations" >>= \r -> return $ if r
then MigrationSuccess
else MigrationError "No such table: schema_migrations"
MigrationDirectory path ->
scriptsInDirectory path >>= goScripts path
MigrationScript name contents ->
validate name contents
MigrationFile name path ->
validate name =<< BS.readFile path
MigrationValidation _ ->
return MigrationSuccess
where
validate name contents =
checkScript con name (md5Hash contents) >>= \r -> case r of
ScriptOk -> do
when verbose $ putStrLn $ "Ok:\t" ++ name
return MigrationSuccess
ScriptNotExecuted -> do
when verbose $ putStrLn $ "Missing:\t" ++ name
return (MigrationError $ "Missing: " ++ name)
ScriptModified _ -> do
when verbose $ putStrLn $ "Checksum mismatch:\t" ++ name
return (MigrationError $ "Checksum mismatch: " ++ name)
goScripts _ [] = return MigrationSuccess
goScripts path (x:xs) = do
r <- validate x =<< BS.readFile (path ++ "/" ++ x)
case r of
e@(MigrationError _) ->
return e
MigrationSuccess ->
goScripts path xs
-- | Checks the status of the script with the given name 'name'.
-- If the script has already been executed, the checksum of the script
-- is compared against the one that was executed.
-- If there is no matching script entry in the database, the script
-- will be executed and its meta-information will be recorded.
checkScript :: Connection -> ScriptName -> Checksum -> IO CheckScriptResult
checkScript con name checksum =
query con q (Only name) >>= \r -> case r of
[] ->
return ScriptNotExecuted
Only actualChecksum:_ | checksum == actualChecksum ->
return ScriptOk
Only actualChecksum:_ ->
return (ScriptModified actualChecksum)
where
q = mconcat
[ "select checksum from schema_migrations "
, "where filename = ? limit 1"
]
-- | Calculates the MD5 checksum of the provided bytestring in base64
-- encoding.
md5Hash :: BS.ByteString -> Checksum
md5Hash = B64.encode . MD5.hash
-- | The checksum type of a migration script.
type Checksum = BS.ByteString
-- | The name of a script. Typically the filename or a custom name
-- when using Haskell migrations.
type ScriptName = String
-- | 'MigrationCommand' determines the action of the 'runMigration' script.
data MigrationCommand
= MigrationInitialization
-- ^ Initializes the database with a helper table containing meta
-- information.
| MigrationDirectory FilePath
-- ^ Executes migrations based on SQL scripts in the provided 'FilePath'
-- in alphabetical order.
| MigrationFile ScriptName FilePath
-- ^ Executes a migration based on script located at the provided
-- 'FilePath'.
| MigrationScript ScriptName BS.ByteString
-- ^ Executes a migration based on the provided bytestring.
| MigrationValidation MigrationCommand
-- ^ Validates the provided MigrationCommand.
deriving (Show, Eq, Read, Ord)
-- | A sum-type denoting the result of a single migration.
data CheckScriptResult
= ScriptOk
-- ^ The script has already been executed and the checksums match.
-- This is good.
| ScriptModified Checksum
-- ^ The script has already been executed and there is a checksum
-- mismatch. This is bad.
| ScriptNotExecuted
-- ^ The script has not been executed, yet. This is good.
deriving (Show, Eq, Read, Ord)
-- | A sum-type denoting the result of a migration.
data MigrationResult a
= MigrationError a
-- ^ There was an error in script migration.
| MigrationSuccess
-- ^ All scripts have been executed successfully.
deriving (Show, Eq, Read, Ord)
-- | The 'MigrationContext' provides an execution context for migrations.
data MigrationContext = MigrationContext
{ migrationContextCommand :: MigrationCommand
-- ^ The action that will be performed by 'runMigration'
, migrationContextVerbose :: Bool
-- ^ Verbosity of the library.
, migrationContextConnection :: Connection
-- ^ The PostgreSQL connection to use for migrations.
}
-- | Produces a list of all executed 'SchemaMigration's.
getMigrations :: Connection -> IO [SchemaMigration]
getMigrations = flip query_ q
where q = mconcat
[ "select filename, checksum, executed_at "
, "from schema_migrations order by executed_at asc"
]
-- | A product type representing a single, executed 'SchemaMigration'.
data SchemaMigration = SchemaMigration
{ schemaMigrationName :: BS.ByteString
-- ^ The name of the executed migration.
, schemaMigrationChecksum :: Checksum
-- ^ The calculated MD5 checksum of the executed script.
, schemaMigrationExecutedAt :: LocalTime
-- ^ A timestamp without timezone of the date of execution of the script.
} deriving (Show, Eq, Read)
instance Ord SchemaMigration where
compare (SchemaMigration nameLeft _ _) (SchemaMigration nameRight _ _) =
compare nameLeft nameRight
instance FromRow SchemaMigration where
fromRow = SchemaMigration <$>
field <*> field <*> field
instance ToRow SchemaMigration where
toRow (SchemaMigration name checksum executedAt) =
[toField name, toField checksum, toField executedAt]