Copyright	(c) 2011 MailRank Inc. (c) 2011-2012 Leon P Smith (c) 2012-2013 Janne Hellsten
License	BSD3
Maintainer	Janne Hellsten <jjhellst@gmail.com>
Portability	portable
Safe Haskell	None
Language	Haskell2010

Database.SQLite.Simple.FromField

Description

The FromField typeclass, for converting a single value in a row returned by a SQL query into a more useful Haskell representation.

A Haskell numeric type is considered to be compatible with all SQLite numeric types that are less accurate than it. For instance, the Haskell Double type is compatible with the SQLite's 32-bit Int type because it can represent a Int exactly. On the other hand, since a Double might lose precision if representing a 64-bit BigInt , the two are not considered compatible.

Synopsis

class FromField a where
- fromField :: FieldParser a
type FieldParser a = Field -> Ok a
data ResultError
- = Incompatible {
  - errSQLType :: String
  - errHaskellType :: String
  - errMessage :: String
  }
- | UnexpectedNull {
  - errSQLType :: String
  - errHaskellType :: String
  - errMessage :: String
  }
- | ConversionFailed {
  - errSQLType :: String
  - errHaskellType :: String
  - errMessage :: String
  }
data Field
fieldData :: Field -> SQLData
returnError :: forall a err. ( Typeable a, Exception err) => ( String -> String -> String -> err) -> Field -> String -> Ok a

Documentation

class FromField a where Source #

A type that may be converted from a SQL type.

Methods

fromField :: FieldParser a Source #

Convert a SQL value to a Haskell value.

Returns a list of exceptions if the conversion fails. In the case of library instances, this will usually be a single ResultError , but may be a UnicodeException .

Implementations of fromField should not retain any references to the Field nor the ByteString arguments after the result has been evaluated to WHNF. Such a reference causes the entire LibPQ. Result to be retained.

For example, the instance for ByteString uses copy to avoid such a reference, and that using bytestring functions such as drop and takeWhile alone will also trigger this memory leak.

Instances

Instances details

FromField Bool Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Bool Source #
FromField Double Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Double Source #
FromField Float Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Float Source #
FromField Int Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Int Source #
FromField Int8 Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Int8 Source #
FromField Int16 Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Int16 Source #
FromField Int32 Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Int32 Source #
FromField Int64 Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Int64 Source #
FromField Integer Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Integer Source #
FromField Word Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Word Source #
FromField Word8 Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Word8 Source #
FromField Word16 Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Word16 Source #
FromField Word32 Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Word32 Source #
FromField Word64 Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Word64 Source #
FromField ByteString Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser ByteString Source #
FromField ByteString Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser ByteString Source #
FromField Text Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Text Source #
FromField Text Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Text Source #
FromField SQLData Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser SQLData Source #
FromField UTCTime Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser UTCTime Source #
FromField Day Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Day Source #
FromField Null Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser Null Source #
FromField [ Char ] Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser [ Char ] Source #
FromField a => FromField ( Maybe a) Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods fromField :: FieldParser ( Maybe a) Source #

type FieldParser a = Field -> Ok a Source #

data ResultError Source #

Exception thrown if conversion from a SQL value to a Haskell value fails.

Constructors

Incompatible	The SQL and Haskell types are not compatible.
Fields errSQLType :: String errHaskellType :: String errMessage :: String
UnexpectedNull	A SQL `NULL` was encountered when the Haskell type did not permit it.
Fields errSQLType :: String errHaskellType :: String errMessage :: String
ConversionFailed	The SQL value could not be parsed, or could not be represented as a valid Haskell value, or an unexpected low-level error occurred (e.g. mismatch between metadata and actual data in a row).
Fields errSQLType :: String errHaskellType :: String errMessage :: String

Instances

Instances details

Eq ResultError Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods (==) :: ResultError -> ResultError -> Bool Source # (/=) :: ResultError -> ResultError -> Bool Source #
Show ResultError Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods showsPrec :: Int -> ResultError -> ShowS Source # show :: ResultError -> String Source # showList :: [ ResultError ] -> ShowS Source #
Exception ResultError Source #
Instance details Defined in Database.SQLite.Simple.FromField Methods toException :: ResultError -> SomeException Source # fromException :: SomeException -> Maybe ResultError Source # displayException :: ResultError -> String Source #

data Field Source #

A Field represents metadata about a particular field

fieldData :: Field -> SQLData Source #

Return the actual SQL data for a database field. This allows user-defined FromField instances to access the SQL data associated with a field being parsed.

returnError :: forall a err. ( Typeable a, Exception err) => ( String -> String -> String -> err) -> Field -> String -> Ok a Source #

Given one of the constructors from ResultError , the field, and an errMessage , this fills in the other fields in the exception value and returns it in a 'Left . SomeException' constructor.