Portability | portable |
---|---|
Stability | experimental |
Maintainer | Bryan O'Sullivan <bos@serpentine.com> |
Safe Haskell | Safe-Infered |
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.
- class Result a where
- convert :: Field -> Maybe ByteString -> a
- data ResultError
- = Incompatible { }
- | UnexpectedNull { }
- | ConversionFailed { }
Documentation
A type that may be converted from a SQL type.
convert :: Field -> Maybe ByteString -> aSource
Convert a SQL value to a Haskell value.
Throws a ResultError
if conversion fails.
data ResultError Source
Exception thrown if conversion from a SQL value to a Haskell value fails.
Incompatible | The SQL and Haskell types are not compatible. |
| |
UnexpectedNull | A SQL |
| |
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). |
|