@@ -1,6 +1,4 @@
1−{-# LANGUAGE FlexibleContexts #-}
2−{-# LANGUAGE RecordWildCards, FlexibleInstances, DefaultSignatures #-}
3−
1+{-# LANGUAGE RecordWildCards #-}
42
53------------------------------------------------------------------------------
64-- |
@@ -9,15 +7,13 @@
97-- License: BSD3
108-- Maintainer: Leon P Smith <leon@melding-monads.com>
119-- Stability: experimental
10+-- Portability: portable
1211--
1312-- The 'FromRow' typeclass, for converting a row of results
1413-- returned by a SQL query into a more useful Haskell representation.
1514--
1615-- Predefined instances are provided for tuples containing up to ten
17−-- elements. The instances for 'Maybe' types return 'Nothing' if all
18−-- the columns that would have been otherwise consumed are null, otherwise
19−-- it attempts a regular conversion.
20−--
16+-- elements.
2117------------------------------------------------------------------------------
2218
2319module Database.PostgreSQL.Simple.FromRow
@@ -28,36 +24,30 @@ module Database.PostgreSQL.Simple.FromRow
2824 , numFieldsRemaining
2925 ) where
3026
31−import Prelude hiding (null)
32−import Control.Applicative (Applicative(..), (<$>), (<|>), (*>), liftA2)
33−import Control.Monad (replicateM, replicateM_)
34−import Control.Monad.Trans.State.Strict
35−import Control.Monad.Trans.Reader
36−import Control.Monad.Trans.Class
37−import Data.ByteString (ByteString)
27+import Control.Applicative (Applicative(..), (<$>))
28+import Control.Monad (replicateM)
29+import Data.ByteString (ByteString)
3830import qualified Data.ByteString.Char8 as B
39−import Data.Vector (Vector)
40−import qualified Data.Vector as V
41−import Database.PostgreSQL.Simple.Types (Only(..))
31+import Database.PostgreSQL.Simple.Types (Only(..))
4232import qualified Database.PostgreSQL.LibPQ as PQ
4333import Database.PostgreSQL.Simple.Internal
44−import Database.PostgreSQL.Simple.Compat
4534import Database.PostgreSQL.Simple.FromField
46−import Database.PostgreSQL.Simple.Ok
47−import Database.PostgreSQL.Simple.Types ((:.)(..), Null)
48−import Database.PostgreSQL.Simple.TypeInfo
35+import Database.PostgreSQL.Simple.Types ((:.)(..))
36+import System.IO.Unsafe (unsafePerformIO)
4937
50−import GHC.Generics
38+import Control.Monad.Trans.State.Strict
39+import Control.Monad.Trans.Reader
40+import Control.Monad.Trans.Class
5141
42+import Data.Vector ((!))
5243
5344-- | A collection type that can be converted from a sequence of fields.
5445-- Instances are provided for tuples up to 10 elements and lists of any length.
5546--
56−-- Note that instances can be defined outside of postgresql-simple, which is
47+-- Note that instances can defined outside of postgresql-simple, which is
5748-- often useful. For example, here's an instance for a user-defined pair:
5849--
59−-- @
60−-- data User = User { name :: String, fileQuota :: Int }
50+-- @data User = User { name :: String, fileQuota :: Int }
6151--
6252-- instance 'FromRow' User where
6353-- fromRow = User \<$\> 'field' \<*\> 'field'
@@ -67,72 +57,45 @@ import GHC.Generics
6757-- in a single row of the query result. Otherwise, a 'ConversionFailed'
6858-- exception will be thrown.
6959--
70−-- You can also derive 'FromRow' for your data type using GHC generics, like
71−-- this:
72−--
73−-- @
74−-- \{-# LANGUAGE DeriveAnyClass \#-}
75−-- \{-# LANGUAGE DeriveGeneric \#-}
76−--
77−-- import "GHC.Generics" ('GHC.Generics.Generic')
78−-- import "Database.PostgreSQL.Simple" ('FromRow')
79−--
80−-- data User = User { name :: String, fileQuota :: Int }
81−-- deriving ('GHC.Generics.Generic', 'FromRow')
82−-- @
83−--
84−-- Note that this only works for product types (e.g. records) and does not
85−-- support sum types or recursive types.
86−--
87−-- Note that 'field' evaluates its result to WHNF, so the caveats listed in
88−-- mysql-simple and very early versions of postgresql-simple no longer apply.
89−-- Instead, look at the caveats associated with user-defined implementations
90−-- of 'fromField'.
60+-- Note that 'field' evaluates it's result to WHNF, so the caveats listed in
61+-- previous versions of postgresql-simple no longer apply. Instead, look
62+-- at the caveats associated with user-defined implementations of 'fromRow'.
9163
9264class FromRow a where
9365 fromRow :: RowParser a
94− default fromRow :: (Generic a, GFromRow (Rep a)) => RowParser a
95− fromRow = to <$> gfromRow
9666
9767getvalue :: PQ.Result -> PQ.Row -> PQ.Column -> Maybe ByteString
98−getvalue result row col = unsafeDupablePerformIO (PQ.getvalue' result row col)
68+getvalue result row col = unsafePerformIO (PQ.getvalue result row col)
9969
10070nfields :: PQ.Result -> PQ.Column
101−nfields result = unsafeDupablePerformIO (PQ.nfields result)
102−
103−getTypeInfoByCol :: Row -> PQ.Column -> Conversion TypeInfo
104−getTypeInfoByCol Row{..} col =
105− Conversion $ \conn -> do
106− oid <- PQ.ftype rowresult col
107− Ok <$> getTypeInfo conn oid
108−
109−getTypenameByCol :: Row -> PQ.Column -> Conversion ByteString
110−getTypenameByCol row col = typname <$> getTypeInfoByCol row col
71+nfields result = unsafePerformIO (PQ.nfields result)
11172
11273fieldWith :: FieldParser a -> RowParser a
11374fieldWith fieldP = RP $ do
11475 let unCol (PQ.Col x) = fromIntegral x :: Int
115− r@Row{..} <- ask
76+ Row{..} <- ask
11677 column <- lift get
11778 lift (put (column + 1))
11879 let ncols = nfields rowresult
11980 if (column >= ncols)
120− then lift $ lift $ do
121− vals <- mapM (getTypenameByCol r) [0..ncols-1]
122− let err = ConversionFailed
123− (show (unCol ncols) ++ " values: " ++ show (map ellipsis vals))
81+ then do
82+ let vals = map (\c -> ( typname (typ (typeinfos ! unCol c))
83+ , fmap ellipsis (getvalue rowresult row c) ))
84+ [0..ncols-1]
85+ convertError = ConversionFailed
86+ (show (unCol ncols) ++ " values: " ++ show vals)
12487 Nothing
12588 ""
12689 ("at least " ++ show (unCol column + 1)
12790 ++ " slots in target type")
12891 "mismatch between number of columns to \
12992 \convert and number in target type"
130− conversionError err
93+ lift (lift (conversionError convertError))
13194 else do
132− let !result = rowresult
133− !typeOid = unsafeDupablePerformIO (PQ.ftype result column)
134− !field' = Field{..}
135− lift (lift (fieldP field' (getvalue result row column)))
95+ let typeinfo = typeinfos ! unCol column
96+ result = rowresult
97+ field = Field{..}
98+ lift (lift (fieldP field (getvalue result row column)))
13699
137100field :: FromField a => RowParser a
138101field = fieldWith fromField
@@ -148,340 +111,57 @@ numFieldsRemaining = RP $ do
148111 column <- lift get
149112 return $! (\(PQ.Col x) -> fromIntegral x) (nfields rowresult - column)
150113
151−null :: RowParser Null
152−null = field
153−
154114instance (FromField a) => FromRow (Only a) where
155115 fromRow = Only <$> field
156116
157−instance (FromField a) => FromRow (Maybe (Only a)) where
158− fromRow = (null *> pure Nothing)
159− <|> (Just <$> fromRow)
160−
161117instance (FromField a, FromField b) => FromRow (a,b) where
162118 fromRow = (,) <$> field <*> field
163119
164−instance (FromField a, FromField b) => FromRow (Maybe (a,b)) where
165− fromRow = (null *> null *> pure Nothing)
166− <|> (Just <$> fromRow)
167−
168120instance (FromField a, FromField b, FromField c) => FromRow (a,b,c) where
169121 fromRow = (,,) <$> field <*> field <*> field
170122
171−instance (FromField a, FromField b, FromField c) => FromRow (Maybe (a,b,c)) where
172− fromRow = (null *> null *> null *> pure Nothing)
173− <|> (Just <$> fromRow)
174−
175123instance (FromField a, FromField b, FromField c, FromField d) =>
176124 FromRow (a,b,c,d) where
177125 fromRow = (,,,) <$> field <*> field <*> field <*> field
178126
179−instance (FromField a, FromField b, FromField c, FromField d) =>
180− FromRow (Maybe (a,b,c,d)) where
181− fromRow = (null *> null *> null *> null *> pure Nothing)
182− <|> (Just <$> fromRow)
183−
184127instance (FromField a, FromField b, FromField c, FromField d, FromField e) =>
185128 FromRow (a,b,c,d,e) where
186129 fromRow = (,,,,) <$> field <*> field <*> field <*> field <*> field
187130
188−instance (FromField a, FromField b, FromField c, FromField d, FromField e) =>
189− FromRow (Maybe (a,b,c,d,e)) where
190− fromRow = (null *> null *> null *> null *> null *> pure Nothing)
191− <|> (Just <$> fromRow)
192−
193131instance (FromField a, FromField b, FromField c, FromField d, FromField e,
194132 FromField f) =>
195133 FromRow (a,b,c,d,e,f) where
196134 fromRow = (,,,,,) <$> field <*> field <*> field <*> field <*> field
197135 <*> field
198136
199−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
200− FromField f) =>
201− FromRow (Maybe (a,b,c,d,e,f)) where
202− fromRow = (null *> null *> null *> null *> null *>
203− null *> pure Nothing)
204− <|> (Just <$> fromRow)
205−
206137instance (FromField a, FromField b, FromField c, FromField d, FromField e,
207138 FromField f, FromField g) =>
208139 FromRow (a,b,c,d,e,f,g) where
209140 fromRow = (,,,,,,) <$> field <*> field <*> field <*> field <*> field
210141 <*> field <*> field
211142
212−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
213− FromField f, FromField g) =>
214− FromRow (Maybe (a,b,c,d,e,f,g)) where
215− fromRow = (null *> null *> null *> null *> null *>
216− null *> null *> pure Nothing)
217− <|> (Just <$> fromRow)
218−
219143instance (FromField a, FromField b, FromField c, FromField d, FromField e,
220144 FromField f, FromField g, FromField h) =>
221145 FromRow (a,b,c,d,e,f,g,h) where
222146 fromRow = (,,,,,,,) <$> field <*> field <*> field <*> field <*> field
223147 <*> field <*> field <*> field
224148
225−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
226− FromField f, FromField g, FromField h) =>
227− FromRow (Maybe (a,b,c,d,e,f,g,h)) where
228− fromRow = (null *> null *> null *> null *> null *>
229− null *> null *> null *> pure Nothing)
230− <|> (Just <$> fromRow)
231−
232149instance (FromField a, FromField b, FromField c, FromField d, FromField e,
233150 FromField f, FromField g, FromField h, FromField i) =>
234151 FromRow (a,b,c,d,e,f,g,h,i) where
235152 fromRow = (,,,,,,,,) <$> field <*> field <*> field <*> field <*> field
236153 <*> field <*> field <*> field <*> field
237154
238−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
239− FromField f, FromField g, FromField h, FromField i) =>
240− FromRow (Maybe (a,b,c,d,e,f,g,h,i)) where
241− fromRow = (null *> null *> null *> null *> null *>
242− null *> null *> null *> null *> pure Nothing)
243− <|> (Just <$> fromRow)
244−
245155instance (FromField a, FromField b, FromField c, FromField d, FromField e,
246156 FromField f, FromField g, FromField h, FromField i, FromField j) =>
247157 FromRow (a,b,c,d,e,f,g,h,i,j) where
248158 fromRow = (,,,,,,,,,) <$> field <*> field <*> field <*> field <*> field
249159 <*> field <*> field <*> field <*> field <*> field
250160
251−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
252− FromField f, FromField g, FromField h, FromField i, FromField j) =>
253− FromRow (Maybe (a,b,c,d,e,f,g,h,i,j)) where
254− fromRow = (null *> null *> null *> null *> null *>
255− null *> null *> null *> null *> null *> pure Nothing)
256− <|> (Just <$> fromRow)
257−
258−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
259− FromField f, FromField g, FromField h, FromField i, FromField j,
260− FromField k) =>
261− FromRow (a,b,c,d,e,f,g,h,i,j,k) where
262− fromRow = (,,,,,,,,,,) <$> field <*> field <*> field <*> field <*> field
263− <*> field <*> field <*> field <*> field <*> field
264− <*> field
265−
266−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
267− FromField f, FromField g, FromField h, FromField i, FromField j,
268− FromField k) =>
269− FromRow (Maybe (a,b,c,d,e,f,g,h,i,j,k)) where
270− fromRow = (null *> null *> null *> null *> null *>
271− null *> null *> null *> null *> null *>
272− null *> pure Nothing)
273− <|> (Just <$> fromRow)
274−
275−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
276− FromField f, FromField g, FromField h, FromField i, FromField j,
277− FromField k, FromField l) =>
278− FromRow (a,b,c,d,e,f,g,h,i,j,k,l) where
279− fromRow = (,,,,,,,,,,,) <$> field <*> field <*> field <*> field <*> field
280− <*> field <*> field <*> field <*> field <*> field
281− <*> field <*> field
282−
283−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
284− FromField f, FromField g, FromField h, FromField i, FromField j,
285− FromField k, FromField l) =>
286− FromRow (Maybe (a,b,c,d,e,f,g,h,i,j,k,l)) where
287− fromRow = (null *> null *> null *> null *> null *>
288− null *> null *> null *> null *> null *>
289− null *> null *> pure Nothing)
290− <|> (Just <$> fromRow)
291−
292−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
293− FromField f, FromField g, FromField h, FromField i, FromField j,
294− FromField k, FromField l, FromField m) =>
295− FromRow (a,b,c,d,e,f,g,h,i,j,k,l,m) where
296− fromRow = (,,,,,,,,,,,,) <$> field <*> field <*> field <*> field <*> field
297− <*> field <*> field <*> field <*> field <*> field
298− <*> field <*> field <*> field
299−
300−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
301− FromField f, FromField g, FromField h, FromField i, FromField j,
302− FromField k, FromField l, FromField m) =>
303− FromRow (Maybe (a,b,c,d,e,f,g,h,i,j,k,l,m)) where
304− fromRow = (null *> null *> null *> null *> null *>
305− null *> null *> null *> null *> null *>
306− null *> null *> null *> pure Nothing)
307− <|> (Just <$> fromRow)
308−
309−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
310− FromField f, FromField g, FromField h, FromField i, FromField j,
311− FromField k, FromField l, FromField m, FromField n) =>
312− FromRow (a,b,c,d,e,f,g,h,i,j,k,l,m,n) where
313− fromRow = (,,,,,,,,,,,,,) <$> field <*> field <*> field <*> field <*> field
314− <*> field <*> field <*> field <*> field <*> field
315− <*> field <*> field <*> field <*> field
316−
317−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
318− FromField f, FromField g, FromField h, FromField i, FromField j,
319− FromField k, FromField l, FromField m, FromField n) =>
320− FromRow (Maybe (a,b,c,d,e,f,g,h,i,j,k,l,m,n)) where
321− fromRow = (null *> null *> null *> null *> null *>
322− null *> null *> null *> null *> null *>
323− null *> null *> null *> null *> pure Nothing)
324− <|> (Just <$> fromRow)
325−
326−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
327− FromField f, FromField g, FromField h, FromField i, FromField j,
328− FromField k, FromField l, FromField m, FromField n, FromField o) =>
329− FromRow (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o) where
330− fromRow = (,,,,,,,,,,,,,,) <$> field <*> field <*> field <*> field <*> field
331− <*> field <*> field <*> field <*> field <*> field
332− <*> field <*> field <*> field <*> field <*> field
333−
334−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
335− FromField f, FromField g, FromField h, FromField i, FromField j,
336− FromField k, FromField l, FromField m, FromField n, FromField o) =>
337− FromRow (Maybe (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o)) where
338− fromRow = (null *> null *> null *> null *> null *>
339− null *> null *> null *> null *> null *>
340− null *> null *> null *> null *> null *> pure Nothing)
341− <|> (Just <$> fromRow)
342−
343−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
344− FromField f, FromField g, FromField h, FromField i, FromField j,
345− FromField k, FromField l, FromField m, FromField n, FromField o,
346− FromField p) =>
347− FromRow (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p) where
348− fromRow = (,,,,,,,,,,,,,,,) <$> field <*> field <*> field <*> field <*> field
349− <*> field <*> field <*> field <*> field <*> field
350− <*> field <*> field <*> field <*> field <*> field
351− <*> field
352−
353−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
354− FromField f, FromField g, FromField h, FromField i, FromField j,
355− FromField k, FromField l, FromField m, FromField n, FromField o,
356− FromField p) =>
357− FromRow (Maybe (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p)) where
358− fromRow = (null *> null *> null *> null *> null *>
359− null *> null *> null *> null *> null *>
360− null *> null *> null *> null *> null *>
361− null *> pure Nothing)
362− <|> (Just <$> fromRow)
363−
364−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
365− FromField f, FromField g, FromField h, FromField i, FromField j,
366− FromField k, FromField l, FromField m, FromField n, FromField o,
367− FromField p, FromField q) =>
368− FromRow (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q) where
369− fromRow = (,,,,,,,,,,,,,,,,) <$> field <*> field <*> field <*> field <*> field
370− <*> field <*> field <*> field <*> field <*> field
371− <*> field <*> field <*> field <*> field <*> field
372− <*> field <*> field
373−
374−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
375− FromField f, FromField g, FromField h, FromField i, FromField j,
376− FromField k, FromField l, FromField m, FromField n, FromField o,
377− FromField p, FromField q) =>
378− FromRow (Maybe (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q)) where
379− fromRow = (null *> null *> null *> null *> null *>
380− null *> null *> null *> null *> null *>
381− null *> null *> null *> null *> null *>
382− null *> null *> pure Nothing)
383− <|> (Just <$> fromRow)
384−
385−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
386− FromField f, FromField g, FromField h, FromField i, FromField j,
387− FromField k, FromField l, FromField m, FromField n, FromField o,
388− FromField p, FromField q, FromField r) =>
389− FromRow (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r) where
390− fromRow = (,,,,,,,,,,,,,,,,,) <$> field <*> field <*> field <*> field <*> field
391− <*> field <*> field <*> field <*> field <*> field
392− <*> field <*> field <*> field <*> field <*> field
393− <*> field <*> field <*> field
394−
395−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
396− FromField f, FromField g, FromField h, FromField i, FromField j,
397− FromField k, FromField l, FromField m, FromField n, FromField o,
398− FromField p, FromField q, FromField r) =>
399− FromRow (Maybe (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r)) where
400− fromRow = (null *> null *> null *> null *> null *>
401− null *> null *> null *> null *> null *>
402− null *> null *> null *> null *> null *>
403− null *> null *> null *> pure Nothing)
404− <|> (Just <$> fromRow)
405−
406−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
407− FromField f, FromField g, FromField h, FromField i, FromField j,
408− FromField k, FromField l, FromField m, FromField n, FromField o,
409− FromField p, FromField q, FromField r, FromField s) =>
410− FromRow (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s) where
411− fromRow = (,,,,,,,,,,,,,,,,,,) <$> field <*> field <*> field <*> field <*> field
412− <*> field <*> field <*> field <*> field <*> field
413− <*> field <*> field <*> field <*> field <*> field
414− <*> field <*> field <*> field <*> field
415−
416−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
417− FromField f, FromField g, FromField h, FromField i, FromField j,
418− FromField k, FromField l, FromField m, FromField n, FromField o,
419− FromField p, FromField q, FromField r, FromField s) =>
420− FromRow (Maybe (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s)) where
421− fromRow = (null *> null *> null *> null *> null *>
422− null *> null *> null *> null *> null *>
423− null *> null *> null *> null *> null *>
424− null *> null *> null *> null *> pure Nothing)
425− <|> (Just <$> fromRow)
426−
427−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
428− FromField f, FromField g, FromField h, FromField i, FromField j,
429− FromField k, FromField l, FromField m, FromField n, FromField o,
430− FromField p, FromField q, FromField r, FromField s, FromField t) =>
431− FromRow (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t) where
432− fromRow = (,,,,,,,,,,,,,,,,,,,) <$> field <*> field <*> field <*> field <*> field
433− <*> field <*> field <*> field <*> field <*> field
434− <*> field <*> field <*> field <*> field <*> field
435− <*> field <*> field <*> field <*> field <*> field
436−
437−instance (FromField a, FromField b, FromField c, FromField d, FromField e,
438− FromField f, FromField g, FromField h, FromField i, FromField j,
439− FromField k, FromField l, FromField m, FromField n, FromField o,
440− FromField p, FromField q, FromField r, FromField s, FromField t) =>
441− FromRow (Maybe (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t)) where
442− fromRow = (null *> null *> null *> null *> null *>
443− null *> null *> null *> null *> null *>
444− null *> null *> null *> null *> null *>
445− null *> null *> null *> null *> null *> pure Nothing)
446− <|> (Just <$> fromRow)
447−
448161instance FromField a => FromRow [a] where
449162 fromRow = do
450163 n <- numFieldsRemaining
451164 replicateM n field
452165
453−instance FromField a => FromRow (Maybe [a]) where
454− fromRow = do
455− n <- numFieldsRemaining
456− (replicateM_ n null *> pure Nothing) <|> (Just <$> replicateM n field)
457−
458−instance FromField a => FromRow (Vector a) where
459− fromRow = do
460− n <- numFieldsRemaining
461− V.replicateM n field
462−
463−instance FromField a => FromRow (Maybe (Vector a)) where
464− fromRow = do
465− n <- numFieldsRemaining
466− (replicateM_ n null *> pure Nothing) <|> (Just <$> V.replicateM n field)
467−
468166instance (FromRow a, FromRow b) => FromRow (a :. b) where
469167 fromRow = (:.) <$> fromRow <*> fromRow
470−
471−
472−
473−-- Type class for default implementation of FromRow using generics
474−class GFromRow f where
475− gfromRow :: RowParser (f p)
476−
477−instance GFromRow f => GFromRow (M1 c i f) where
478− gfromRow = M1 <$> gfromRow
479−
480−instance (GFromRow f, GFromRow g) => GFromRow (f :*: g) where
481− gfromRow = liftA2 (:*:) gfromRow gfromRow
482−
483−instance (FromField a) => GFromRow (K1 R a) where
484− gfromRow = K1 <$> field
485−
486−instance GFromRow U1 where
487− gfromRow = pure U1