| Copyright |
(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.FromRow
Description
The
FromRow
typeclass, for converting a row of results
returned by a SQL query into a more useful Haskell representation.
Predefined instances are provided for tuples containing up to ten elements.
Documentation
class GFromRow f where Source #
Generic derivation of
FromRow
.
Instantiating
FromRow
can in some cases be quite tedious. Luckily
we can derive it generically in some cases where the type at hand
has a
Generic
instance. The current implementation only works
for a (n-ary) product types. So we would not be able to
e.g. derive a
FromRow
instance for
data Bool = True | False
We
can
, however, derive a generic instance for the
User
type
(see the example in
FromRow
).
Since: 0.4.18.1
class FromRow a where Source #
A collection type that can be converted from a sequence of fields. Instances are provided for tuples up to 10 elements and lists of any length.
Note that instances can defined outside of sqlite-simple, which is often useful. For example, here's an instance for a user-defined pair:
data User = User { name :: String, fileQuota :: Int }
instance FromRow User where
fromRow = User <$> field <*> field
The number of calls to
field
must match the number of fields returned
in a single row of the query result. Otherwise, a
ConversionFailed
exception will be thrown.
Note the caveats associated with user-defined implementations of
fromRow
.
Generic implementation
Since version 0.4.18.1 it is possible in some cases to derive a
generic implementation for
FromRow
. With a
Generic
instance
for
User
, the example above could be written:
instance FromRow User where
With
-XDeriveAnyClass -XDerivingStrategies
the same can be written:
deriving anyclass instance FromRow User
For more details refer to
GFromRow
.
Minimal complete definition
Nothing
Methods
Instances
Instances
| Monad RowParser Source # | |
| Functor RowParser Source # | |
| Applicative RowParser Source # | |
| Alternative RowParser Source # | |
| MonadPlus RowParser Source # | |
fieldWith :: FieldParser a -> RowParser a Source #