Mockmigrate example

Cookbook.md

@@ -40,6 +40,7 @@ For non-Yesod code, see also [Snippets](https://github.com/yesodweb/yesod-cookbo
 * [Adding Seed data to Scaffolded Site](https://github.com/yesodweb/yesod-cookbook/blob/master/cookbook/Adding-Seed-Data-to-Scaffolded-Site.md)
 * [Handling exception in persistence](https://github.com/yesodweb/yesod-cookbook/blob/master/cookbook/Handling-Persistence-Exception.md)
 * [Builtin Postgresql types with Persistent](https://github.com/yesodweb/yesod-cookbook/blob/master/cookbook/CustomPostgresqlTypes.md)
+* [Modelling Schema with Persistent](./cookbook/modelling-schema.md)
 
 ## State
 

cookbook/modelling-schema.md

@@ -0,0 +1,54 @@
+You can use persistent to model your DB schema and see the generated
+sql query without even the presence of the actual database
+server. Example code demonstrating it:
+
+``` haskell
+#!/usr/bin/env stack
+{- stack
+     --resolver lts-6.11
+     --install-ghc
+     runghc
+     --package persistent
+     --package persistent-postgresql
+     --package persistent-template
+-}
+
+{-# LANGUAGE EmptyDataDecls             #-}
+{-# LANGUAGE FlexibleContexts           #-}
+{-# LANGUAGE GADTs                      #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE MultiParamTypeClasses      #-}
+{-# LANGUAGE OverloadedStrings          #-}
+{-# LANGUAGE QuasiQuotes                #-}
+{-# LANGUAGE TemplateHaskell            #-}
+{-# LANGUAGE TypeFamilies               #-}
+
+import           Database.Persist
+import           Database.Persist.Postgresql
+import           Database.Persist.TH
+
+share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persistLowerCase|
+Person
+    name String
+    age Int Maybe
+    address Int
+    deriving Show
+BlogPost
+    title String
+    authorId PersonId
+    deriving Show
+|]
+
+main :: IO ()
+main = mockMigration migrateAll
+```
+
+On execution, this will produce:
+
+``` shellsession
+sibi { ~/scripts }-> ./migration.hs
+CREATe TABLE "person"("id" SERIAL8  PRIMARY KEY UNIQUE,"name" VARCHAR NOT NULL,"age" INT8 NULL,"address" INT8 NOT NULL)
+CREATe TABLE "blog_post"("id" SERIAL8  PRIMARY KEY UNIQUE,"title" VARCHAR NOT NULL,"author_id" INT8 NOT NULL)
+ALTER TABLE "blog_post" ADD CONSTRAINT "blog_post_author_id_fkey" FOREIGN KEY("author_id") REFERENCES "person"("id")
+```
+