Hoogle Search

Within LTS Haskell 24.3 (ghc-9.10.2)

Note that Stackage only displays results for the latest LTS and Nightly snapshot. Learn more.

Exact lookup

1. class PersistField a => PersistFieldSql a

   persistent	Database.Persist.Sql

   Tells Persistent what database column type should be used to store a Haskell type.

   Examples

   Simple Boolean Alternative

   data Switch = On | Off
   deriving (Show, Eq)
   
   instance PersistField Switch where
   toPersistValue s = case s of
   On -> PersistBool True
   Off -> PersistBool False
   fromPersistValue (PersistBool b) = if b then Right On else Right Off
   fromPersistValue x = Left $ "File.hs: When trying to deserialize a Switch: expected PersistBool, received: " <> T.pack (show x)
   
   instance PersistFieldSql Switch where
   sqlType _ = SqlBool
   

   Non-Standard Database Types

   If your database supports non-standard types, such as Postgres' uuid, you can use SqlOther to use them:

   import qualified Data.UUID as UUID
   instance PersistField UUID where
   toPersistValue = PersistLiteralEncoded . toASCIIBytes
   fromPersistValue (PersistLiteralEncoded uuid) =
   case fromASCIIBytes uuid of
   Nothing -> Left $ "Model/CustomTypes.hs: Failed to deserialize a UUID; received: " <> T.pack (show uuid)
   Just uuid' -> Right uuid'
   fromPersistValue x = Left $ "File.hs: When trying to deserialize a UUID: expected PersistLiteralEncoded, received: "-- >  <> T.pack (show x)
   
   instance PersistFieldSql UUID where
   sqlType _ = SqlOther "uuid"
   

   User Created Database Types

   Similarly, some databases support creating custom types, e.g. Postgres' DOMAIN and ENUM features. You can use SqlOther to specify a custom type:

   CREATE DOMAIN ssn AS text
   CHECK ( value ~ '^[0-9]{9}$');
   

   instance PersistFieldSQL SSN where
   sqlType _ = SqlOther "ssn"
   

   CREATE TYPE rainbow_color AS ENUM ('red', 'orange', 'yellow', 'green', 'blue', 'indigo', 'violet');
   

   instance PersistFieldSQL RainbowColor where
   sqlType _ = SqlOther "rainbow_color"
   

2. data PersistentSqlException

   persistent	Database.Persist.Sql

   No documentation available.

3. newtype PersistUnsafeMigrationException

   persistent	Database.Persist.Sql.Migration

   An exception indicating that Persistent refused to run some unsafe migrations. Contains a list of pairs where the Bool tracks whether the migration was unsafe (True means unsafe), and the Sql is the sql statement for the migration.

4. PersistUnsafeMigrationException :: [(Bool, Sql)] -> PersistUnsafeMigrationException

   persistent	Database.Persist.Sql.Migration

   No documentation available.

5. PersistArray :: [PersistValue] -> PersistValue

   persistent	Database.Persist.Types

   Intended especially for PostgreSQL backend for text arrays

6. PersistBool :: Bool -> PersistValue

   persistent	Database.Persist.Types

   No documentation available.

7. PersistByteString :: ByteString -> PersistValue

   persistent	Database.Persist.Types

   No documentation available.

8. PersistDay :: Day -> PersistValue

   persistent	Database.Persist.Types

   No documentation available.

9. pattern PersistDbSpecific :: ByteString -> PersistValue

   persistent	Database.Persist.Types

   Deprecated: Deprecated since 2.11 because of inconsistent escaping behavior across backends. The Postgres backend escapes these values, while the MySQL backend does not. If you are using this, please switch to PersistLiteral_ and provide a relevant LiteralType for your conversion.

10. PersistDouble :: Double -> PersistValue

    persistent	Database.Persist.Types

    No documentation available.

Page 7 of many | Previous | Next