example applies migration to real Postgres instance

beam-postgres/examples/app/RunMigration.hs

@@ -0,0 +1,18 @@
+module RunMigration where
+
+import Prelude
+import Database.PostgreSQL.Simple (connect, close, ConnectInfo(..))
+import Pagila.Schema (migrateDB)
+
+-- https://hackage.haskell.org/package/postgresql-simple-0.7.0.0/docs/Database-PostgreSQL-Simple.html#t:ConnectInfo
+connInfo :: ConnectInfo
+connInfo = ConnectInfo "localhost" (read "5432") "postgres" "foo" "postgres"
+
+main :: IO ()
+main = do
+  putStrLn "Running migration..."
+  c <- connect connInfo
+
+  _ <- migrateDB c
+
+  close c

beam-postgres/examples/pagila.cabal

@@ -22,6 +22,7 @@ library
                       scientific,
                       bytestring,
                       text,
+                      exceptions,
                       postgresql-simple,
                       beam-core,
                       beam-postgres,
@@ -32,22 +33,29 @@ library
 executable pagila
     import:           warnings
     main-is:          Main.hs
-
-    -- Modules included in this executable, other than Main.
-    -- other-modules:
-
     build-depends:    base,
                       pagila,
                       text,
                       bytestring,
                       beam-core,
                       beam-postgres,
                       beam-migrate
-
-    -- Directories containing source files.
     hs-source-dirs:   app
+    default-language: Haskell2010
 
-    -- Base language which the package is written in.
+executable pagila-migration
+    import:           warnings
+    main-is:          RunMigration.hs
+    ghc-options:      -main-is RunMigration
+    build-depends:    base,
+                      pagila,
+                      text,
+                      bytestring,
+                      beam-core,
+                      beam-postgres,
+                      beam-migrate,
+                      postgresql-simple
+    hs-source-dirs:   app
     default-language: Haskell2010
 
 test-suite pagila-test

beam-postgres/examples/readme.md

@@ -1,3 +1,30 @@
 # Pagila example
 
-`cabal run` to see rendering of Postgres migration.
+There are two executables:
+
+### 1. `cabal run`
+`cabal run` to see rendering of Postgres migration. This converts the Haskell to SQL statements and prints these to the console.
+
+### 2. Destructive: apply migration to Postgres instance
+
+Hard-code your Postgres connection parameters into `app/RunMigration.hs` `connInfo`.
+Then `cabal run pagila-migration`. *This will overwrite your Postgres data*.
+
+The result will be the Pagila database schema in your Postgres instance:
+```
+postgres=# \d
+                      List of relations
+ Schema |             Name              |   Type   |  Owner
+--------+-------------------------------+----------+----------
+ public | actor                         | table    | postgres
+ public | actor_actor_id_seq            | sequence | postgres
+ public | address                       | table    | postgres
+ public | address_address_id_seq        | sequence | postgres
+ public | beam_migration                | table    | postgres
+ public | beam_version                  | table    | postgres
+ public | category                      | table    | postgres
+.
+.
+.
+```
+

beam-postgres/examples/src/Pagila/Schema.hs

@@ -1,7 +1,9 @@
 {-# LANGUAGE OverloadedStrings #-}
 module Pagila.Schema
   ( module Pagila.Schema.V0002
-  , migration, db ) where
+  , migration, migrateDB, dbSettings ) where
+
+import           Database.PostgreSQL.Simple
 
 import Pagila.Schema.V0002 hiding (migration)
 
@@ -13,11 +15,24 @@ import Control.Arrow ( (>>>) )
 import Database.Beam (DatabaseSettings)
 import Database.Beam.Migrate.Types ( CheckedDatabaseSettings, MigrationSteps, unCheckDatabase
                                    , evaluateDatabase, migrationStep)
-import Database.Beam.Postgres (Postgres)
+import Database.Beam.Postgres (Postgres, runBeamPostgresDebug)
+import Database.Beam.Migrate.Simple (BringUpToDateHooks, bringUpToDateWithHooks, defaultUpToDateHooks, runIrreversibleHook)
+import qualified Database.Beam.Postgres.Migrate as Pg
 
 migration :: MigrationSteps Postgres () (CheckedDatabaseSettings Postgres Pagila.Schema.V0002.PagilaDb)
 migration = migrationStep "Initial commit" V0001.migration >>>
             migrationStep "Add film actor, inventory, rental table" V0002.migration
 
-db :: DatabaseSettings Postgres Pagila.Schema.V0002.PagilaDb
-db = unCheckDatabase (evaluateDatabase migration)
+dbSettings :: DatabaseSettings Postgres Pagila.Schema.V0002.PagilaDb
+dbSettings = unCheckDatabase (evaluateDatabase migration)
+
+allowDestructive :: (MonadFail m) => BringUpToDateHooks m
+allowDestructive =
+  defaultUpToDateHooks
+    { runIrreversibleHook = return True
+    }
+
+migrateDB :: Connection -> IO (Maybe (CheckedDatabaseSettings Postgres Pagila.Schema.V0002.PagilaDb))
+migrateDB conn =
+  runBeamPostgresDebug putStrLn conn
+    $ bringUpToDateWithHooks allowDestructive Pg.migrationBackend migration