khibino/haskell-relational-record
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Add Maybe derivation rule of ToSql type.

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This commit is contained in:
Kei Hibino 2013-07-29 15:46:00 +09:00
parent 4885ebe91d
commit e685f6488a
1 changed files with 14 additions and 1 deletions
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15
DB-record/src/Database/Record/ToSql.hs
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@ -39,7 +39,9 @@ import Data.Array (listArray, (!))
import Data.Set (toList, fromList, (\\))
import Database.Record.Persistable
(PersistableRecord, Persistable(persistable))
(PersistableSqlType, runPersistableNullValue, PersistableType (persistableType),
PersistableRecordWidth, runPersistableRecordWidth, PersistableWidth(persistableWidth),
PersistableRecord, Persistable(persistable))
import Database.Record.KeyConstraint
(Primary, Unique, KeyConstraint, HasKeyConstraint(keyConstraint), unique, indexes)
import qualified Database.Record.Persistable as Persistable
@ -71,6 +73,12 @@ recordToSql' = recordSerializer persistable
(<&>) :: RecordToSql q a -> RecordToSql q b -> RecordToSql q (a, b)
ra <&> rb = RecordToSql (\(a, b) -> runFromRecord ra a ++ runFromRecord rb b)
-- | Derivation rule of 'RecordToSql' proof object for Haskell 'Maybe' type.
maybeRecord :: PersistableSqlType q -> PersistableRecordWidth a -> RecordToSql q a -> RecordToSql q (Maybe a)
maybeRecord qt w (RecordToSql f) = RecordToSql d where
d (Just r) = f r
d Nothing = replicate (runPersistableRecordWidth w) (runPersistableNullValue qt)
infixl 4 <&>
@ -84,6 +92,11 @@ class ToSql q a where
instance (ToSql q a, ToSql q b) => ToSql q (a, b) where
recordToSql = recordToSql <&> recordToSql
-- | Inference rule of 'RecordToSql' proof object which can convert
-- from Haskell 'Maybe' type into list of SQL type ['q'].
instance (PersistableType q, PersistableWidth a, ToSql q a) => ToSql q (Maybe a) where
recordToSql = maybeRecord persistableType persistableWidth recordToSql
-- | Inference rule of 'RecordToSql' proof object which can convert
-- from Haskell unit () type into /empty/ list of SQL type ['q'].
instance ToSql q () where