From bff41673c49ae9b108375ba584302f92f453071d Mon Sep 17 00:00:00 2001
From: fr33domlover <fr33domlover@rel4tion.org>
Date: Thu, 1 Sep 2016 16:30:39 +0000
Subject: [PATCH] Migration: Specify default value when adding non-null column

---
 src/Database/Persist/Schema.hs            |  3 ++-
 src/Database/Persist/Schema/PostgreSQL.hs | 16 +++++++++++++++-
 src/Database/Persist/Schema/Sql.hs        | 17 +++++++++++++----
 3 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/src/Database/Persist/Schema.hs b/src/Database/Persist/Schema.hs
index 88a9b8d..96362d0 100644
--- a/src/Database/Persist/Schema.hs
+++ b/src/Database/Persist/Schema.hs
@@ -79,7 +79,8 @@ class PersistSchema backend where
     removeEntity
         :: MonadIO m => EntityName -> SchemaT backend m ()
     addField
-        :: MonadIO m => EntityName -> Field -> SchemaT backend m ()
+        :: MonadIO m
+        => EntityName -> Field -> Maybe Text -> SchemaT backend m ()
     renameField
         :: MonadIO m
         => EntityName -> FieldName -> FieldName -> SchemaT backend m ()
diff --git a/src/Database/Persist/Schema/PostgreSQL.hs b/src/Database/Persist/Schema/PostgreSQL.hs
index ca677cd..17d904a 100644
--- a/src/Database/Persist/Schema/PostgreSQL.hs
+++ b/src/Database/Persist/Schema/PostgreSQL.hs
@@ -20,6 +20,7 @@ where
 
 import Prelude
 
+import Data.Monoid ((<>))
 import Data.Text (Text)
 import Database.Persist.Sql (SqlBackend)
 import Database.Persist.Types (SqlType (..))
@@ -92,9 +93,12 @@ schemaBackend = SqlSchemaBackend
     , ssbDropTable = \ table -> mconcat
         [ "DROP TABLE ", table2sql table
         ]
-    , ssbAddColumn = \ table column -> mconcat
+    , ssbAddColumn = \ table column mdef -> mconcat
         [ "ALTER TABLE ", table2sql table
         , " ADD COLUMN ", columnSql column
+        , case mdef of
+            Nothing -> T.empty
+            Just t  -> " DEFAULT " <> t
         ]
     , ssbRenameColumn = \ table old new -> mconcat
         [ "ALTER TABLE ", table2sql table
@@ -118,6 +122,16 @@ schemaBackend = SqlSchemaBackend
         , " SET ", column2sql column, " = ", val
         , " WHERE ", column2sql column, " IS NULL"
         ]
+    , ssbDefColumn = \ table column val -> mconcat
+        [ "ALTER TABLE ", table2sql table
+        , " ALTER COLUMN ", column2sql column
+        , " SET DEFAULT ", val
+        ]
+    , ssbUndefColumn = \ table column -> mconcat
+        [ "ALTER TABLE ", table2sql table
+        , " ALTER COLUMN ", column2sql column
+        , " DROP DEFAULT"
+        ]
     , ssbDropColumn = \ table column -> mconcat
         [ "ALTER TABLE ", table2sql table
         , " DROP COLUMN ", column2sql column
diff --git a/src/Database/Persist/Schema/Sql.hs b/src/Database/Persist/Schema/Sql.hs
index 54309b9..fc0dca1 100644
--- a/src/Database/Persist/Schema/Sql.hs
+++ b/src/Database/Persist/Schema/Sql.hs
@@ -26,11 +26,13 @@ where
 
 import Prelude
 
+import Control.Monad (when)
 import Control.Monad.IO.Class (MonadIO)
 import Control.Monad.Trans.Class (lift)
 import Control.Monad.Trans.Reader (ask)
 import Data.Char (isUpper, toLower)
 import Data.Foldable (traverse_)
+import Data.Maybe (isJust)
 import Data.Text (Text)
 import Database.Persist.Sql (Sql, SqlBackend, rawExecute)
 import Database.Persist.Types (SqlType)
@@ -101,11 +103,13 @@ instance PersistSchema SqlBackend where
         , ssbCreateTable    :: TableName -> [Column] -> Sql
         , ssbRenameTable    :: TableName -> TableName -> Sql
         , ssbDropTable      :: TableName -> Sql
-        , ssbAddColumn      :: TableName -> Column -> Sql
+        , ssbAddColumn      :: TableName -> Column -> Maybe Text -> Sql
         , ssbRenameColumn   :: TableName -> ColumnName -> ColumnName -> Sql
         , ssbRetypeColumn   :: TableName -> ColumnName -> SqlType -> Sql
         , ssbRenullColumn   :: TableName -> ColumnName -> MaybeNull -> Sql
         , ssbUnnullColumn   :: TableName -> ColumnName -> Text -> Sql
+        , ssbDefColumn      :: TableName -> ColumnName -> Text -> Sql
+        , ssbUndefColumn    :: TableName -> ColumnName -> Sql
         , ssbDropColumn     :: TableName -> ColumnName -> Sql
         , ssbAddUnique
             :: TableName -> ConstraintName -> [ColumnName] -> Sql
@@ -123,11 +127,16 @@ instance PersistSchema SqlBackend where
     removeEntity name = do
         ssb <- ask
         exec $ ssbDropTable ssb $ entity2table name
-    addField ent (Field name typ mnull) = do
+    addField ent (Field name typ mnull) mdef = do
         ssb <- ask
         exec $
-            ssbAddColumn ssb (entity2table ent) $
-            Column (field2column name) (type2sql ssb typ) mnull
+            ssbAddColumn ssb
+                (entity2table ent)
+                (Column (field2column name) (type2sql ssb typ) mnull)
+                mdef
+        when (isJust mdef) $
+            exec $
+            ssbUndefColumn ssb (entity2table ent) (field2column name)
     renameField entity old new = do
         ssb <- ask
         exec $