Database.MySQL.Simple.Result

The Result 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 MySQL numeric types that are less accurate than it. For instance, the Haskell Double type is compatible with the MySQL Long type because it can represent a Long exactly. On the other hand, since a Double might lose precision if representing a LongLong, the two are not considered compatible.

Documentation

class FromField a where

A type that can be converted from a ByteString. Any type which is an instance of this class, and is Typeable, can use the default implementation of Result. This provides a method of implementing a decoder for any text-like column, such as TEXT, BLOB, or JSON, instead of implementing Result directly.

The first component of the tuple returned by fromField is a list of acceptable column types, expressed in terms of Type.

Since: 0.4.8

Methods

fromField :: ([Type], ByteString -> Either String a)

Instances

FromField UTCTime

Defined in Database.MySQL.Simple.Result

Methods

fromField :: ([Type], ByteString -> Either String UTCTime)

FromField TimeOfDay

Defined in Database.MySQL.Simple.Result

Methods

fromField :: ([Type], ByteString -> Either String TimeOfDay)

class Result a where

A type that may be converted from a SQL type.

A default implementation is provided for any type which is an instance of both FromField and Typeable, providing a simple mechanism for user-defined decoding from text- or blob-like fields (including JSON).

Minimal complete definition

Nothing

Methods

convert :: Field -> Maybe ByteString -> a

Convert a SQL value to a Haskell value.

Throws a ResultError if conversion fails.

default convert :: (Typeable a, FromField a) => Field -> Maybe ByteString -> a

Instances

Result Int16

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Int16

Result Int32

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Int32

Result Int64

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Int64

Result Int8

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Int8

Result Word16

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Word16

Result Word32

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Word32

Result Word64

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Word64

Result ByteString

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> ByteString

Result ByteString

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString0 -> ByteString

Result Text

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Text

Result Text

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Text

Result Day

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Day

Result UTCTime

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> UTCTime

Result TimeOfDay

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> TimeOfDay

Result Word8

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Word8

Result Integer

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Integer

Result Bool

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Bool

Result Double

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Double

Result Float

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Float

Result Int

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Int

Result Word

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Word

Result (Ratio Integer)

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Ratio Integer

Result a => Result (Maybe a)

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> Maybe a

Result [Char]

Defined in Database.MySQL.Simple.Result

Methods

convert :: Field -> Maybe ByteString -> [Char]

data ResultError

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
• errFieldName :: String
• errMessage :: String

UnexpectedNull

A SQL NULL was encountered when the Haskell type did not permit it.

Fields

• errSQLType :: String
• errHaskellType :: String
• errFieldName :: 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
• errFieldName :: String
• errMessage :: String

Instances

Exception ResultError

Defined in Database.MySQL.Simple.Result

Methods

toException :: ResultError -> SomeException

fromException :: SomeException -> Maybe ResultError

displayException :: ResultError -> String

Show ResultError

Defined in Database.MySQL.Simple.Result

Methods

showsPrec :: Int -> ResultError -> ShowS

show :: ResultError -> String

showList :: [ResultError] -> ShowS

Eq ResultError

Defined in Database.MySQL.Simple.Result

Methods

(==) :: ResultError -> ResultError -> Bool

(/=) :: ResultError -> ResultError -> Bool