@@ -1,14 +1,18 @@
1−{-# LANGUAGE BangPatterns, DeriveDataTypeable, OverloadedStrings #-}
2−{-# LANGUAGE DoAndIfThenElse, RecordWildCards, NamedFieldPuns #-}
1+{-# LANGUAGE DeriveDataTypeable #-}
2+{-# LANGUAGE NamedFieldPuns #-}
3+{-# LANGUAGE OverloadedStrings #-}
4+{-# LANGUAGE PatternGuards #-}
5+{-# LANGUAGE RecordWildCards #-}
6+{-# LANGUAGE ViewPatterns #-}
7+
38------------------------------------------------------------------------------
49-- |
510-- Module: Database.PostgreSQL.Simple
611-- Copyright: (c) 2011 MailRank, Inc.
7−-- (c) 2011 Leon P Smith
12+-- (c) 2011-2012 Leon P Smith
813-- License: BSD3
914-- Maintainer: Leon P Smith <leon@melding-monads.com>
1015-- Stability: experimental
11−-- Portability: portable
1216--
1317-- A mid-level client library for the PostgreSQL database, aimed at ease of
1418-- use and high performance.
@@ -38,6 +42,9 @@ module Database.PostgreSQL.Simple
3842 -- ** Modifying multiple rows at once
3943 -- $many
4044
45+ -- ** @RETURNING@: modifications that return results
46+ -- $returning
47+
4148 -- * Extracting results
4249 -- $result
4350
@@ -48,32 +55,54 @@ module Database.PostgreSQL.Simple
4855 -- $types
4956
5057 -- * Types
51− Base.ConnectInfo(..)
52− , Connection
58+ Connection
5359 , Query
60+ , ToRow
61+ , FromRow
5462 , In(..)
5563 , Binary(..)
5664 , Only(..)
65+ , (:.)(..)
5766 -- ** Exceptions
58− , FormatError(fmtMessage, fmtQuery, fmtParams)
59− , QueryError(qeMessage, qeQuery)
60− , ResultError(errSQLType, errHaskellType, errMessage)
67+ , SomePostgreSqlException(..)
68+ , SqlError(..)
69+ , PQ.ExecStatus(..)
70+ , FormatError(..)
71+ , QueryError(..)
72+ , ResultError(..)
6173 -- * Connection management
62− , Base.connect
6374 , Base.connectPostgreSQL
64− , Base.postgreSQLConnectionString
65− , Base.defaultConnectInfo
6675 , Base.close
76+ , Base.connect
77+ , Base.withConnect
78+ , Base.ConnectInfo(..)
79+ , Base.defaultConnectInfo
80+ , Base.postgreSQLConnectionString
6781 -- * Queries that return results
6882 , query
6983 , query_
70−{--
84+ -- ** Queries taking parser as argument
85+ , queryWith
86+ , queryWith_
7187 -- * Queries that stream results
88+ , FoldOptions(..)
89+ , FetchQuantity(..)
90+ , defaultFoldOptions
7291 , fold
92+ , foldWithOptions
7393 , fold_
94+ , foldWithOptions_
7495 , forEach
7596 , forEach_
76−--}
97+ , returning
98+ -- ** Queries that stream results taking a parser as an argument
99+ , foldWith
100+ , foldWithOptionsAndParser
101+ , foldWith_
102+ , foldWithOptionsAndParser_
103+ , forEachWith
104+ , forEachWith_
105+ , returningWith
77106 -- * Statements that do not return results
78107 , execute
79108 , execute_
@@ -81,6 +110,7 @@ module Database.PostgreSQL.Simple
81110-- , Base.insertID
82111 -- * Transaction handling
83112 , withTransaction
113+ , withSavepoint
84114-- , Base.autocommit
85115 , begin
86116 , commit
@@ -90,55 +120,27 @@ module Database.PostgreSQL.Simple
90120 , formatQuery
91121 ) where
92122
93−import Blaze.ByteString.Builder (Builder, fromByteString, toByteString)
94−import Blaze.ByteString.Builder.Char8 (fromChar)
95−import Control.Applicative ((<$>), pure)
96−import Control.Concurrent.MVar
97−import Control.Exception (Exception, bracket, onException, throw, throwIO)
98−import Control.Monad (forM)
99−import Control.Monad.Fix (fix)
100−import Data.ByteString (ByteString)
101−-- import qualified Data.ByteString as B (unpack)
102−import Data.Char(ord)
103−import Data.Int (Int64)
104−import qualified Data.IntMap as IntMap
105−import Data.List (intersperse)
106−import Data.Monoid (mappend, mconcat)
107−import Data.Typeable (Typeable)
108−--import Database.MySQL.Base (Connection, Result)
109−--import Database.MySQL.Base.Types (Field)
110−import Database.PostgreSQL.Simple.BuiltinTypes (oid2builtin, builtin2typname)
111−import Database.PostgreSQL.Simple.Param (Action(..), inQuotes)
112−import Database.PostgreSQL.Simple.QueryParams (QueryParams(..))
113−import Database.PostgreSQL.Simple.Result (ResultError(..))
114−import Database.PostgreSQL.Simple.QueryResults (QueryResults(..))
115−-- import Database.PostgreSQL.Simple.Result (ResultError(..))
116−import Database.PostgreSQL.Simple.Types (Binary(..), In(..), Only(..), Query(..))
117−import Database.PostgreSQL.Simple.Internal as Base
123+import Data.ByteString.Builder (Builder, byteString, char8)
124+import Control.Applicative ((<$>))
125+import Control.Exception as E
126+import Data.ByteString (ByteString)
127+import Data.Int (Int64)
128+import Data.List (intersperse)
129+import Data.Monoid (mconcat)
130+import Database.PostgreSQL.Simple.Compat ((<>), toByteString)
131+import Database.PostgreSQL.Simple.Cursor
132+import Database.PostgreSQL.Simple.FromField (ResultError(..))
133+import Database.PostgreSQL.Simple.FromRow (FromRow(..))
134+import Database.PostgreSQL.Simple.ToField (Action(..))
135+import Database.PostgreSQL.Simple.ToRow (ToRow(..))
136+import Database.PostgreSQL.Simple.Types
137+ ( Binary(..), In(..), Only(..), Query(..), (:.)(..) )
138+import Database.PostgreSQL.Simple.Internal as Base
139+import Database.PostgreSQL.Simple.Internal.PQResultUtils
140+import Database.PostgreSQL.Simple.Transaction
118141import qualified Database.PostgreSQL.LibPQ as PQ
119−import Text.Regex.PCRE.Light (compile, caseless, match)
120142import qualified Data.ByteString.Char8 as B
121−--import qualified Database.MySQL.Base as Base
122−
123−-- | Exception thrown if a 'Query' could not be formatted correctly.
124−-- This may occur if the number of \'@?@\' characters in the query
125−-- string does not match the number of parameters provided.
126−data FormatError = FormatError {
127− fmtMessage :: String
128− , fmtQuery :: Query
129− , fmtParams :: [ByteString]
130− } deriving (Eq, Show, Typeable)
131−
132−instance Exception FormatError
133143
134−-- | Exception thrown if 'query' is used to perform an @INSERT@-like
135−-- operation, or 'execute' is used to perform a @SELECT@-like operation.
136−data QueryError = QueryError {
137− qeMessage :: String
138− , qeQuery :: Query
139− } deriving (Eq, Show, Typeable)
140−
141−instance Exception QueryError
142144
143145-- | Format a query string.
144146--
@@ -150,11 +152,11 @@ instance Exception QueryError
150152--
151153-- Throws 'FormatError' if the query string could not be formatted
152154-- correctly.
153−formatQuery :: QueryParams q => Connection -> Query -> q -> IO ByteString
155+formatQuery :: ToRow q => Connection -> Query -> q -> IO ByteString
154156formatQuery conn q@(Query template) qs
155157 | null xs && '?' `B.notElem` template = return template
156158 | otherwise = toByteString <$> buildQuery conn q template xs
157− where xs = renderParams qs
159+ where xs = toRow qs
158160
159161-- | Format a query string with a variable number of rows.
160162--
@@ -169,106 +171,208 @@ formatQuery conn q@(Query template) qs
169171--
170172-- Throws 'FormatError' if the query string could not be formatted
171173-- correctly.
172−formatMany :: (QueryParams q) => Connection -> Query -> [q] -> IO ByteString
174+formatMany :: (ToRow q) => Connection -> Query -> [q] -> IO ByteString
173175formatMany _ q [] = fmtError "no rows supplied" q []
174176formatMany conn q@(Query template) qs = do
175− case match re template [] of
176− Just [_,before,qbits,after] -> do
177− bs <- mapM (buildQuery conn q qbits . renderParams) qs
178− return . toByteString . mconcat $ fromByteString before :
179− intersperse (fromChar ',') bs ++
180− [fromByteString after]
181− _ -> error "foo"
177+ case parseTemplate template of
178+ Just (before, qbits, after) -> do
179+ bs <- mapM (buildQuery conn q qbits . toRow) qs
180+ return . toByteString . mconcat $ byteString before :
181+ intersperse (char8 ',') bs ++
182+ [byteString after]
183+ Nothing -> fmtError "syntax error in multi-row template" q []
184+
185+-- Split the input string into three pieces, @before@, @qbits@, and @after@,
186+-- following this grammar:
187+--
188+-- start: ^ before qbits after $
189+-- before: ([^?]* [^?\w])? 'VALUES' \s*
190+-- qbits: '(' \s* '?' \s* (',' \s* '?' \s*)* ')'
191+-- after: [^?]*
192+--
193+-- \s: [ \t\n\r\f]
194+-- \w: [A-Z] | [a-z] | [\x80-\xFF] | '_' | '$' | [0-9]
195+--
196+-- This would be much more concise with some sort of regex engine.
197+-- 'formatMany' used to use pcre-light instead of this hand-written parser,
198+-- but pcre is a hassle to install on Windows.
199+parseTemplate :: ByteString -> Maybe (ByteString, ByteString, ByteString)
200+parseTemplate template =
201+ -- Convert input string to uppercase, to facilitate searching.
202+ search $ B.map toUpper_ascii template
182203 where
183− re = compile "^([^?]+\\bvalues\\s*)\
184− \(\\(\\s*[?](?:\\s*,\\s*[?])*\\s*\\))\
185− \([^?]*)$"
186− [caseless]
204+ -- Search for the next occurrence of "VALUES"
205+ search bs =
206+ case B.breakSubstring "VALUES" bs of
207+ (x, y)
208+ -- If "VALUES" is not present in the string, or any '?' characters
209+ -- were encountered prior to it, fail.
210+ | B.null y || ('?' `B.elem` x)
211+ -> Nothing
212+
213+ -- If "VALUES" is preceded by an identifier character (a.k.a. \w),
214+ -- try the next occurrence.
215+ | not (B.null x) && isIdent (B.last x)
216+ -> search $ B.drop 6 y
217+
218+ -- Otherwise, we have a legitimate "VALUES" token.
219+ | otherwise
220+ -> parseQueryBits $ skipSpace $ B.drop 6 y
221+
222+ -- Parse '(' \s* '?' \s* . If this doesn't match
223+ -- (and we don't consume a '?'), look for another "VALUES".
224+ --
225+ -- qb points to the open paren (if present), meaning it points to the
226+ -- beginning of the "qbits" production described above. This is why we
227+ -- pass it down to finishQueryBits.
228+ parseQueryBits qb
229+ | Just ('(', skipSpace -> bs1) <- B.uncons qb
230+ , Just ('?', skipSpace -> bs2) <- B.uncons bs1
231+ = finishQueryBits qb bs2
232+ | otherwise
233+ = search qb
234+
235+ -- Parse (',' \s* '?' \s*)* ')' [^?]* .
236+ --
237+ -- Since we've already consumed at least one '?', there's no turning back.
238+ -- The parse has to succeed here, or the whole thing fails
239+ -- (because we don't allow '?' to appear outside of the VALUES list).
240+ finishQueryBits qb bs0
241+ | Just (')', bs1) <- B.uncons bs0
242+ = if '?' `B.elem` bs1
243+ then Nothing
244+ else Just $ slice3 template qb bs1
245+ | Just (',', skipSpace -> bs1) <- B.uncons bs0
246+ , Just ('?', skipSpace -> bs2) <- B.uncons bs1
247+ = finishQueryBits qb bs2
248+ | otherwise
249+ = Nothing
250+
251+ -- Slice a string into three pieces, given the start offset of the second
252+ -- and third pieces. Each "offset" is actually a tail of the uppercase
253+ -- version of the template string. Its length is used to infer the offset.
254+ --
255+ -- It is important to note that we only slice the original template.
256+ -- We don't want our all-caps trick messing up the actual query string.
257+ slice3 source p1 p2 =
258+ (s1, s2, source'')
259+ where
260+ (s1, source') = B.splitAt (B.length source - B.length p1) source
261+ (s2, source'') = B.splitAt (B.length p1 - B.length p2) source'
262+
263+ toUpper_ascii c | c >= 'a' && c <= 'z' = toEnum (fromEnum c - 32)
264+ | otherwise = c
265+
266+ -- Based on the definition of {ident_cont} in src/backend/parser/scan.l
267+ -- in the PostgreSQL source. No need to check [a-z], since we converted
268+ -- the whole string to uppercase.
269+ isIdent c = (c >= '0' && c <= '9')
270+ || (c >= 'A' && c <= 'Z')
271+ || (c >= '\x80' && c <= '\xFF')
272+ || c == '_'
273+ || c == '$'
274+
275+ -- Based on {space} in scan.l
276+ isSpace_ascii c = (c == ' ') || (c >= '\t' && c <= '\r')
277+
278+ skipSpace = B.dropWhile isSpace_ascii
187279
188−escapeStringConn conn s = withConnection conn $ \c -> do
189− PQ.escapeStringConn c s
190280
191281buildQuery :: Connection -> Query -> ByteString -> [Action] -> IO Builder
192−buildQuery conn q template xs = zipParams (split template) <$> mapM sub xs
193− where quote = inQuotes . fromByteString . maybe undefined id
194− sub (Plain b) = pure b
195− sub (Escape s) = quote <$> escapeStringConn conn s
196− sub (Many ys) = mconcat <$> mapM sub ys
197− split s = fromByteString h : if B.null t then [] else split (B.tail t)
198− where (h,t) = B.break (=='?') s
199− zipParams (t:ts) (p:ps) = t `mappend` p `mappend` zipParams ts ps
282+buildQuery conn q template xs =
283+ zipParams (split template) <$> mapM (buildAction conn q xs) xs
284+ where split s =
285+ -- This part escapes double '??'s to make literal '?'s possible
286+ -- in PostgreSQL queries using the JSON operators: @?@, @?|@ and @?&@
287+ let (h,t) = breakOnSingleQuestionMark s
288+ in byteString h
289+ : if B.null t
290+ then []
291+ else split (B.tail t)
292+ zipParams (t:ts) (p:ps) = t <> p <> zipParams ts ps
200293 zipParams [t] [] = t
201− zipParams _ _ = fmtError (show (B.count '?' template) ++
202− " '?' characters, but " ++
294+ zipParams _ _ = fmtError (show countSingleQs ++
295+ " single '?' characters, but " ++
203296 show (length xs) ++ " parameters") q xs
297+ countSingleQs = go 0 template
298+ where go i "" = (i :: Int)
299+ go i bs = case qms of
300+ ("?","?") -> go i nextQMBS
301+ ("?",_) -> go (i+1) nextQMBS
302+ _ -> i
303+ where qms = B.splitAt 1 qmBS
304+ (qmBS,nextQMBS) = B.splitAt 2 qmBS'
305+ qmBS' = B.dropWhile (/= '?') bs
204306
205307-- | Execute an @INSERT@, @UPDATE@, or other SQL query that is not
206308-- expected to return results.
207309--
208310-- Returns the number of rows affected.
209311--
210−-- Throws 'FormatError' if the query could not be formatted correctly.
211−execute :: (QueryParams q) => Connection -> Query -> q -> IO Int64
312+-- Throws 'FormatError' if the query could not be formatted correctly, or
313+-- a 'SqlError' exception if the backend returns an error.
314+execute :: (ToRow q) => Connection -> Query -> q -> IO Int64
212315execute conn template qs = do
213316 result <- exec conn =<< formatQuery conn template qs
214317 finishExecute conn template result
215318
216−-- | A version of 'execute' that does not perform query substitution.
217−execute_ :: Connection -> Query -> IO Int64
218−execute_ conn q@(Query stmt) = do
219− result <- exec conn stmt
220− finishExecute conn q result
221−
222319-- | Execute a multi-row @INSERT@, @UPDATE@, or other SQL query that is not
223320-- expected to return results.
224321--
225−-- Returns the number of rows affected.
322+-- Returns the number of rows affected. If the list of parameters is empty,
323+-- this function will simply return 0 without issuing the query to the backend.
324+-- If this is not desired, consider using the 'Values' constructor instead.
226325--
227−-- Throws 'FormatError' if the query could not be formatted correctly.
228−executeMany :: (QueryParams q) => Connection -> Query -> [q] -> IO Int64
326+-- Throws 'FormatError' if the query could not be formatted correctly, or
327+-- a 'SqlError' exception if the backend returns an error.
328+--
329+-- For example, here's a command that inserts two rows into a table
330+-- with two columns:
331+--
332+-- @
333+-- executeMany c [sql|
334+-- INSERT INTO sometable VALUES (?,?)
335+-- |] [(1, \"hello\"),(2, \"world\")]
336+-- @
337+--
338+-- Here's an canonical example of a multi-row update command:
339+--
340+-- @
341+-- executeMany c [sql|
342+-- UPDATE sometable
343+-- SET y = upd.y
344+-- FROM (VALUES (?,?)) as upd(x,y)
345+-- WHERE sometable.x = upd.x
346+-- |] [(1, \"hello\"),(2, \"world\")]
347+-- @
348+
349+executeMany :: (ToRow q) => Connection -> Query -> [q] -> IO Int64
229350executeMany _ _ [] = return 0
230351executeMany conn q qs = do
231352 result <- exec conn =<< formatMany conn q qs
232353 finishExecute conn q result
233354
234−finishExecute :: Connection -> Query -> PQ.Result -> IO Int64
235−finishExecute conn q result = do
236− status <- PQ.resultStatus result
237− case status of
238− PQ.EmptyQuery -> fail "empty query" -- FIXME: error message
239− PQ.CommandOk -> do
240− ncols <- PQ.nfields result
241− if ncols /= 0
242− then throwIO $ QueryError ("execute resulted in " ++ show ncols ++
243− "-column result") q
244− else do
245− nstr <- PQ.cmdTuples result
246− return $ case nstr of
247− Nothing -> 0 -- is this appropriate?
248− Just str -> toInteger str
249− PQ.TuplesOk -> do
250− ncols <- PQ.nfields result
251− throwIO $ QueryError ("execute resulted in " ++ show ncols ++
252− "-column result") q
253− PQ.CopyIn -> fail "FIXME: postgresql-simple does not currently support COPY IN"
254− PQ.CopyOut -> fail "FIXME: postgresql-simple does not currently support COPY OUT"
255− _ -> do
256− errormsg <- maybe "" id <$> PQ.resultErrorMessage result
257− statusmsg <- PQ.resStatus status
258− state <- maybe "" id <$> PQ.resultErrorField result PQ.DiagSqlstate
259− throw $ SqlError { sqlState = state
260− , sqlNativeError = 0 -- FIXME
261− , sqlErrorMsg = B.concat [ "execute: ", statusmsg
262− , ": ", errormsg ]}
263− where
264− toInteger str = B.foldl' delta 0 str
265− where
266− delta acc c =
267− if '0' <= c && c <= '9'
268− then 10 * acc + fromIntegral (ord c - ord '0')
269− else error ("finishExecute: not an int: " ++ B.unpack str)
270−
355+-- | Execute @INSERT ... RETURNING@, @UPDATE ... RETURNING@, or other SQL
356+-- query that accepts multi-row input and is expected to return results.
357+-- Note that it is possible to write
358+-- @'query' conn "INSERT ... RETURNING ..." ...@
359+-- in cases where you are only inserting a single row, and do not need
360+-- functionality analogous to 'executeMany'.
361+--
362+-- If the list of parameters is empty, this function will simply return @[]@
363+-- without issuing the query to the backend. If this is not desired,
364+-- consider using the 'Values' constructor instead.
365+--
366+-- Throws 'FormatError' if the query could not be formatted correctly.
367+returning :: (ToRow q, FromRow r) => Connection -> Query -> [q] -> IO [r]
368+returning = returningWith fromRow
271369
370+-- | A version of 'returning' taking parser as argument
371+returningWith :: (ToRow q) => RowParser r -> Connection -> Query -> [q] -> IO [r]
372+returningWith _ _ _ [] = return []
373+returningWith parser conn q qs = do
374+ result <- exec conn =<< formatMany conn q qs
375+ finishQueryWith parser conn q result
272376
273377-- | Perform a @SELECT@ or other SQL query that is expected to return
274378-- results. All results are retrieved and converted before this
@@ -285,33 +389,44 @@ finishExecute conn q result = do
285389-- using 'execute' instead of 'query').
286390--
287391-- * 'ResultError': result conversion failed.
288−query :: (QueryParams q, QueryResults r)
289− => Connection -> Query -> q -> IO [r]
290−query conn template qs = do
291− result <- exec conn =<< formatQuery conn template qs
292− finishQuery conn template result
392+--
393+-- * 'SqlError': the postgresql backend returned an error, e.g.
394+-- a syntax or type error, or an incorrect table or column name.
395+query :: (ToRow q, FromRow r) => Connection -> Query -> q -> IO [r]
396+query = queryWith fromRow
293397
294398-- | A version of 'query' that does not perform query substitution.
295−query_ :: (QueryResults r) => Connection -> Query -> IO [r]
296−query_ conn q@(Query que) = do
399+query_ :: (FromRow r) => Connection -> Query -> IO [r]
400+query_ = queryWith_ fromRow
401+
402+-- | A version of 'query' taking parser as argument
403+queryWith :: ToRow q => RowParser r -> Connection -> Query -> q -> IO [r]
404+queryWith parser conn template qs = do
405+ result <- exec conn =<< formatQuery conn template qs
406+ finishQueryWith parser conn template result
407+
408+-- | A version of 'query_' taking parser as argument
409+queryWith_ :: RowParser r -> Connection -> Query -> IO [r]
410+queryWith_ parser conn q@(Query que) = do
297411 result <- exec conn que
298− finishQuery conn q result
299−{--
412+ finishQueryWith parser conn q result
413+
300414-- | Perform a @SELECT@ or other SQL query that is expected to return
301415-- results. Results are streamed incrementally from the server, and
302416-- consumed via a left fold.
303417--
304−-- The result consumer must be carefully written to execute
305−-- quickly. If the consumer is slow, server resources will be tied up,
306−-- and other clients may not be able to update the tables from which
307−-- the results are being streamed.
308−--
309418-- When dealing with small results, it may be simpler (and perhaps
310419-- faster) to use 'query' instead.
311420--
312421-- This fold is /not/ strict. The stream consumer is responsible for
313422-- forcing the evaluation of its result to avoid space leaks.
314423--
424+-- This is implemented using a database cursor. As such, this requires
425+-- a transaction. This function will detect whether or not there is a
426+-- transaction in progress, and will create a 'ReadCommitted' 'ReadOnly'
427+-- transaction if needed. The cursor is given a unique temporary name,
428+-- so the consumer may itself call fold.
429+--
315430-- Exceptions that may be thrown:
316431--
317432-- * 'FormatError': the query string could not be formatted correctly.
@@ -320,164 +435,202 @@ query_ conn q@(Query que) = do
320435-- using 'execute' instead of 'query').
321436--
322437-- * 'ResultError': result conversion failed.
323−fold :: (QueryParams q, QueryResults r) =>
324− Connection
325− -> Query -- ^ Query template.
326− -> q -- ^ Query parameters.
327− -> a -- ^ Initial state for result consumer.
328− -> (a -> r -> IO a) -- ^ Result consumer.
329− -> IO a
330−fold conn template qs z f = do
331− Base.query conn =<< formatQuery conn template qs
332− finishFold conn template z f
333−--}
334−{--
438+--
439+-- * 'SqlError': the postgresql backend returned an error, e.g.
440+-- a syntax or type error, or an incorrect table or column name.
441+fold :: ( FromRow row, ToRow params )
442+ => Connection
443+ -> Query
444+ -> params
445+ -> a
446+ -> (a -> row -> IO a)
447+ -> IO a
448+fold = foldWithOptions defaultFoldOptions
449+
450+-- | A version of 'fold' taking a parser as an argument
451+foldWith :: ( ToRow params )
452+ => RowParser row
453+ -> Connection
454+ -> Query
455+ -> params
456+ -> a
457+ -> (a -> row -> IO a)
458+ -> IO a
459+foldWith = foldWithOptionsAndParser defaultFoldOptions
460+
461+-- | Number of rows to fetch at a time. 'Automatic' currently defaults
462+-- to 256 rows, although it might be nice to make this more intelligent
463+-- based on e.g. the average size of the rows.
464+data FetchQuantity
465+ = Automatic
466+ | Fixed !Int
467+
468+data FoldOptions
469+ = FoldOptions {
470+ fetchQuantity :: !FetchQuantity,
471+ transactionMode :: !TransactionMode
472+ }
473+
474+-- | defaults to 'Automatic', and 'TransactionMode' 'ReadCommitted' 'ReadOnly'
475+defaultFoldOptions :: FoldOptions
476+defaultFoldOptions = FoldOptions {
477+ fetchQuantity = Automatic,
478+ transactionMode = TransactionMode ReadCommitted ReadOnly
479+ }
480+
481+-- | The same as 'fold', but this provides a bit more control over
482+-- lower-level details. Currently, the number of rows fetched per
483+-- round-trip to the server and the transaction mode may be adjusted
484+-- accordingly. If the connection is already in a transaction,
485+-- then the existing transaction is used and thus the 'transactionMode'
486+-- option is ignored.
487+foldWithOptions :: ( FromRow row, ToRow params )
488+ => FoldOptions
489+ -> Connection
490+ -> Query
491+ -> params
492+ -> a
493+ -> (a -> row -> IO a)
494+ -> IO a
495+foldWithOptions opts = foldWithOptionsAndParser opts fromRow
496+
497+-- | A version of 'foldWithOptions' taking a parser as an argument
498+foldWithOptionsAndParser :: (ToRow params)
499+ => FoldOptions
500+ -> RowParser row
501+ -> Connection
502+ -> Query
503+ -> params
504+ -> a
505+ -> (a -> row -> IO a)
506+ -> IO a
507+foldWithOptionsAndParser opts parser conn template qs a f = do
508+ q <- formatQuery conn template qs
509+ doFold opts parser conn template (Query q) a f
510+
335511-- | A version of 'fold' that does not perform query substitution.
336−fold_ :: (QueryResults r) =>
512+fold_ :: (FromRow r) =>
337513 Connection
338514 -> Query -- ^ Query.
339515 -> a -- ^ Initial state for result consumer.
340516 -> (a -> r -> IO a) -- ^ Result consumer.
341517 -> IO a
342−fold_ conn q@(Query que) z f = do
343− Base.query conn que
344− finishFold conn q z f
345−--}
346−{--
518+fold_ = foldWithOptions_ defaultFoldOptions
519+
520+-- | A version of 'fold_' taking a parser as an argument
521+foldWith_ :: RowParser r
522+ -> Connection
523+ -> Query
524+ -> a
525+ -> (a -> r -> IO a)
526+ -> IO a
527+foldWith_ = foldWithOptionsAndParser_ defaultFoldOptions
528+
529+foldWithOptions_ :: (FromRow r) =>
530+ FoldOptions
531+ -> Connection
532+ -> Query -- ^ Query.
533+ -> a -- ^ Initial state for result consumer.
534+ -> (a -> r -> IO a) -- ^ Result consumer.
535+ -> IO a
536+foldWithOptions_ opts conn query' a f = doFold opts fromRow conn query' query' a f
537+
538+-- | A version of 'foldWithOptions_' taking a parser as an argument
539+foldWithOptionsAndParser_ :: FoldOptions
540+ -> RowParser r
541+ -> Connection
542+ -> Query -- ^ Query.
543+ -> a -- ^ Initial state for result consumer.
544+ -> (a -> r -> IO a) -- ^ Result consumer.
545+ -> IO a
546+foldWithOptionsAndParser_ opts parser conn query' a f = doFold opts parser conn query' query' a f
547+
548+doFold :: FoldOptions
549+ -> RowParser row
550+ -> Connection
551+ -> Query
552+ -> Query
553+ -> a
554+ -> (a -> row -> IO a)
555+ -> IO a
556+doFold FoldOptions{..} parser conn _template q a0 f = do
557+ stat <- withConnection conn PQ.transactionStatus
558+ case stat of
559+ PQ.TransIdle -> withTransactionMode transactionMode conn go
560+ PQ.TransInTrans -> go
561+ PQ.TransActive -> fail "foldWithOpts FIXME: PQ.TransActive"
562+ -- This _shouldn't_ occur in the current incarnation of
563+ -- the library, as we aren't using libpq asynchronously.
564+ -- However, it could occur in future incarnations of
565+ -- this library or if client code uses the Internal module
566+ -- to use raw libpq commands on postgresql-simple connections.
567+ PQ.TransInError -> fail "foldWithOpts FIXME: PQ.TransInError"
568+ -- This should be turned into a better error message.
569+ -- It is probably a bad idea to automatically roll
570+ -- back the transaction and start another.
571+ PQ.TransUnknown -> fail "foldWithOpts FIXME: PQ.TransUnknown"
572+ -- Not sure what this means.
573+ where
574+ declare =
575+ declareCursor conn q
576+ fetch cursor a =
577+ foldForwardWithParser cursor parser chunkSize f a
578+
579+ go = bracket declare closeCursor $ \cursor ->
580+ let loop a = fetch cursor a >>=
581+ \r -> case r of
582+ Left x -> return x
583+ Right x -> loop x
584+ in loop a0
585+
586+-- FIXME: choose the Automatic chunkSize more intelligently
587+-- One possibility is to use the type of the results, although this
588+-- still isn't a perfect solution, given that common types (e.g. text)
589+-- are of highly variable size.
590+-- A refinement of this technique is to pick this number adaptively
591+-- as results are read in from the database.
592+ chunkSize = case fetchQuantity of
593+ Automatic -> 256
594+ Fixed n -> n
595+
347596-- | A version of 'fold' that does not transform a state value.
348−forEach :: (QueryParams q, QueryResults r) =>
597+forEach :: (ToRow q, FromRow r) =>
349598 Connection
350599 -> Query -- ^ Query template.
351600 -> q -- ^ Query parameters.
352601 -> (r -> IO ()) -- ^ Result consumer.
353602 -> IO ()
354−forEach conn template qs = fold conn template qs () . const
603+forEach = forEachWith fromRow
355604{-# INLINE forEach #-}
356605
606+-- | A version of 'forEach' taking a parser as an argument
607+forEachWith :: ( ToRow q )
608+ => RowParser r
609+ -> Connection
610+ -> Query
611+ -> q
612+ -> (r -> IO ())
613+ -> IO ()
614+forEachWith parser conn template qs = foldWith parser conn template qs () . const
615+{-# INLINE forEachWith #-}
616+
357617-- | A version of 'forEach' that does not perform query substitution.
358−forEach_ :: (QueryResults r) =>
618+forEach_ :: (FromRow r) =>
359619 Connection
360620 -> Query -- ^ Query template.
361621 -> (r -> IO ()) -- ^ Result consumer.
362622 -> IO ()
363−forEach_ conn template = fold_ conn template () . const
623+forEach_ = forEachWith_ fromRow
364624{-# INLINE forEach_ #-}
365−--}
366625
367−forM' :: (Ord n, Num n) => n -> n -> (n -> IO a) -> IO [a]
368−forM' lo hi m = loop hi []
369− where
370− loop !n !as
371− | n < lo = return as
372− | otherwise = do
373− a <- m n
374− loop (n-1) (a:as)
375−
376−finishQuery :: (QueryResults r) => Connection -> Query -> PQ.Result -> IO [r]
377−finishQuery conn q result = do
378− status <- PQ.resultStatus result
379− case status of
380− PQ.EmptyQuery -> fail "empty query" -- FIXME: error message
381− PQ.CommandOk -> do
382− throwIO $ QueryError "query resulted in a command response" q
383− PQ.TuplesOk -> do
384− ncols <- PQ.nfields result
385− fields <- forM' 0 (ncols-1) $ \column -> do
386− type_oid <- PQ.ftype result column
387− typename <- getTypename conn type_oid
388− return Field{..}
389− nrows <- PQ.ntuples result
390− forM' 0 (nrows-1) $ \row -> do
391− values <- forM' 0 (ncols-1) (\col -> PQ.getvalue' result row col)
392− case convertResults fields values of
393− Left err -> throwIO err
394− Right a -> return a
395− PQ.CopyIn -> fail "FIXME: postgresql-simple does not currently support COPY IN"
396− PQ.CopyOut -> fail "FIXME: postgresql-simple does not currently support COPY OUT"
397− _ -> do
398− errormsg <- maybe "" id <$> PQ.resultErrorMessage result
399− statusmsg <- PQ.resStatus status
400− state <- maybe "" id <$> PQ.resultErrorField result PQ.DiagSqlstate
401− throw $ SqlError { sqlState = state
402− , sqlNativeError = 0 -- FIXME
403− , sqlErrorMsg = B.concat [ "execute: ", statusmsg
404− , ": ", errormsg ]}
405−
406−{--
407−withResult (Base.storeResult conn) q $ \r fs -> do
408− status <-
409−/ flip fix [] $ \loop acc -> do
410− row <- Base.fetchRow r
411− case row of
412− [] -> return (reverse acc)
413− _ -> let !c = convertResults fs row
414− in loop (c:acc)
415−--}
416−{--
417−finishFold :: (QueryResults r) =>
418− Connection -> Query -> a -> (a -> r -> IO a) -> IO a
419−finishFold conn q z0 f = withResult (Base.useResult conn) q $ \r fs ->
420− flip fix z0 $ \loop z -> do
421− row <- Base.fetchRow r
422− case row of
423− [] -> return z
424− _ -> (f z $! convertResults fs row) >>= loop
425−--}
426−{--
427−withResult :: (IO Result) -> Query -> (Result -> [Field] -> IO a) -> IO a
428−withResult fetchResult q act = bracket fetchResult Base.freeResult $ \r -> do
429− ncols <- Base.fieldCount (Right r)
430− if ncols == 0
431− then throwIO $ QueryError "query resulted in zero-column result" q
432− else act r =<< Base.fetchFields r
433−--}
434−-- | Execute an action inside a SQL transaction.
435−--
436−-- This function initiates a transaction with a \"@begin
437−-- transaction@\" statement, then executes the supplied action. If
438−-- the action succeeds, the transaction will be completed with
439−-- 'Base.commit' before this function returns.
440−--
441−-- If the action throws /any/ kind of exception (not just a
442−-- PostgreSQL-related exception), the transaction will be rolled back using
443−-- 'rollback', then the exception will be rethrown.
444−withTransaction :: Connection -> IO a -> IO a
445−withTransaction conn act = do
446− _ <- begin conn
447− r <- act `onException` rollback conn
448− commit conn
449− return r
450−
451−-- | Rollback a transaction.
452−-- rollback :: (MonadCatchIO m,MonadIO m) => Connection -> m ()
453−rollback :: Connection -> IO ()
454−rollback conn = do
455− _ <- execute_ conn "ABORT"
456− return ()
457−
458−-- | Commit a transaction.
459−-- commit :: (MonadCatchIO m,MonadIO m) => Connection -> m ()
460−commit :: Connection -> IO ()
461−commit conn = do
462− _ <- execute_ conn "COMMIT"
463− return ()
464−
465−-- | Begin a transaction.
466−-- begin :: (MonadCatchIO m,MonadIO m) => Connection -> m ()
467−begin :: Connection -> IO ()
468−begin conn = do
469− _ <- execute_ conn "BEGIN"
470− return ()
471−
472−fmtError :: String -> Query -> [Action] -> a
473−fmtError msg q xs = throw FormatError {
474− fmtMessage = msg
475− , fmtQuery = q
476− , fmtParams = map twiddle xs
477− }
478− where twiddle (Plain b) = toByteString b
479− twiddle (Escape s) = s
480− twiddle (Many ys) = B.concat (map twiddle ys)
626+forEachWith_ :: RowParser r
627+ -> Connection
628+ -> Query
629+ -> (r -> IO ())
630+ -> IO ()
631+forEachWith_ parser conn template = foldWith_ parser conn template () . const
632+{-# INLINE forEachWith_ #-}
633+
481634
482635-- $use
483636--
@@ -505,9 +658,11 @@ fmtError msg q xs = throw FormatError {
505658-- >
506659-- > import Database.PostgreSQL.Simple
507660-- >
661+-- > hello :: IO Int
508662-- > hello = do
509−-- > conn <- connect defaultConnectInfo
510−-- > query conn "select 2 + 2"
663+-- > conn <- connectPostgreSQL ""
664+-- > [Only i] <- query_ conn "select 2 + 2"
665+-- > return i
511666--
512667-- A 'Query' value does not represent the actual query that will be
513668-- executed, but is a template for constructing the final query.
@@ -554,7 +709,7 @@ fmtError msg q xs = throw FormatError {
554709-- Automated type inference means that you will often be able to avoid
555710-- supplying explicit type signatures for the elements of a tuple.
556711-- However, sometimes the compiler will not be able to infer your
557−-- types. Consider a care where you write a numeric literal in a
712+-- types. Consider a case where you write a numeric literal in a
558713-- parameter tuple:
559714--
560715-- > query conn "select ? + ?" (40,2)
@@ -568,15 +723,30 @@ fmtError msg q xs = throw FormatError {
568723-- The same kind of problem can arise with string literals if you have
569724-- the @OverloadedStrings@ language extension enabled. Again, just
570725-- use an explicit type signature if this happens.
726+--
727+-- Finally, remember that the compiler must be able to infer the type
728+-- of a query's /results/ as well as its parameters. We might like
729+-- the following example to work:
730+--
731+-- > print =<< query_ conn "select 2 + 2"
732+--
733+-- Unfortunately, while a quick glance tells us that the result type
734+-- should be a single row containing a single numeric column, the
735+-- compiler has no way to infer what the types are. We can easily fix
736+-- this by providing an explicit type annotation:
737+--
738+-- > xs <- query_ conn "select 2 + 2"
739+-- > print (xs :: [Only Int])
571740
572741-- $only_param
573742--
574743-- Haskell lacks a single-element tuple type, so if you have just one
575−-- value you want substituted into a query, what should you do?
744+-- value you want substituted into a query or a single-column result,
745+-- what should you do?
576746--
577747-- The obvious approach would appear to be something like this:
578748--
579−-- > instance (Param a) => QueryParam a where
749+-- > instance (ToField a) => ToRow a where
580750-- > ...
581751--
582752-- Unfortunately, this wreaks havoc with type inference, so we take a
@@ -587,6 +757,9 @@ fmtError msg q xs = throw FormatError {
587757--
588758-- > execute conn "insert into users (first_name) values (?)"
589759-- > ["Nuala"]
760+--
761+-- A row of /n/ query results is represented using an /n/-tuple, so
762+-- you should use 'Only' to represent a single-column result.
590763
591764-- $in
592765--
@@ -604,7 +777,7 @@ fmtError msg q xs = throw FormatError {
604777-- Here's an example:
605778--
606779-- > query conn "select * from users where first_name in ?" $
607−-- > In ["Anna", "Boris", "Carla"]
780+-- > Only $ In ["Anna", "Boris", "Carla"]
608781--
609782-- If your 'In'-wrapped list is empty, the string @\"(null)\"@ will be
610783-- substituted instead, to ensure that your clause remains
@@ -632,7 +805,7 @@ fmtError msg q xs = throw FormatError {
632805-- * There must be no other \"@?@\" characters anywhere in your
633806-- template.
634807--
635−-- * There must one or more \"@?@\" in the parentheses.
808+-- * There must be one or more \"@?@\" in the parentheses.
636809--
637810-- * Extra white space is fine.
638811--
@@ -653,10 +826,26 @@ fmtError msg q xs = throw FormatError {
653826-- > insert into users (first_name,last_name) values
654827-- > ('Boris','Karloff'),('Ed','Wood')
655828
829+-- $returning
830+--
831+-- PostgreSQL supports returning values from data manipulation statements
832+-- such as @INSERT@ and @UPDATE@. You can use these statements by
833+-- using 'query' instead of 'execute'. For multi-tuple inserts,
834+-- use 'returning' instead of 'executeMany'.
835+--
836+-- For example, were there an auto-incrementing @id@ column and
837+-- timestamp column @t@ that defaulted to the present time for the
838+-- @sales@ table, then the following query would insert two new
839+-- sales records and also return their new @id@s and timestamps.
840+--
841+-- > let q = "insert into sales (amount, label) values (?,?) returning id, t"
842+-- > xs :: [(Int, UTCTime)] <- query conn q (15,"Sawdust")
843+-- > ys :: [(Int, UTCTime)] <- returning conn q [(20,"Chips"),(300,"Wood")]
844+
656845-- $result
657846--
658847-- The 'query' and 'query_' functions return a list of values in the
659−-- 'QueryResults' typeclass. This class performs automatic extraction
848+-- 'FromRow' typeclass. This class performs automatic extraction
660849-- and type conversion of rows from a query result.
661850--
662851-- Here is a simple example of how to extract results:
@@ -687,7 +876,7 @@ fmtError msg q xs = throw FormatError {
687876--
688877-- Although SQL can accommodate @NULL@ as a value for any of these
689878-- types, Haskell cannot. If your result contains columns that may be
690−-- @NULL@, be sure that you use 'Maybe' in those positions of of your
879+-- @NULL@, be sure that you use 'Maybe' in those positions of your
691880-- tuple.
692881--
693882-- > (Text, Maybe Int, Int)
@@ -711,13 +900,13 @@ fmtError msg q xs = throw FormatError {
711900--
712901-- * For numeric types, any Haskell type that can accurately represent
713902-- all values of the given PostgreSQL type is considered \"compatible\".
714−-- For instance, you can always extract a PostgreSQL 16-bit @SMALLINT@
903+-- For instance, you can always extract a PostgreSQL 16-bit @SMALLINT@
715904-- column to a Haskell 'Int'. The Haskell 'Float' type can accurately
716−-- represent a @SMALLINT@, so it is considered compatble with those types.
905+-- represent a @SMALLINT@, so it is considered compatible with those types.
717906--
718907-- * A numeric compatibility check is based only on the type of a
719908-- column, /not/ on its values. For instance, a PostgreSQL 64-bit
720−-- @BIGINT@ column will be considered incompatible with a Haskell
909+-- @BIGINT@ column will be considered incompatible with a Haskell
721910-- 'Int16', even if it contains the value @1@.
722911--
723912-- * If a numeric incompatibility is found, 'query' will throw a
@@ -727,25 +916,3 @@ fmtError msg q xs = throw FormatError {
727916-- UTF-8. If you use some other encoding, decoding may fail or give
728917-- wrong results. In such cases, write a @newtype@ wrapper and a
729918-- custom 'Result' instance to handle your encoding.
730−
731−getTypename :: Connection -> PQ.Oid -> IO ByteString
732−getTypename conn@Connection{..} oid =
733− case oid2builtin oid of
734− Just builtin -> return $! builtin2typname builtin
735− Nothing -> modifyMVar connectionObjects $ \oidmap -> do
736− case IntMap.lookup (oid2int oid) oidmap of
737− Just name -> return (oidmap, name)
738− Nothing -> do
739− names <- query conn "SELECT typname FROM pg_type WHERE oid=?"
740− (Only oid)
741− name <- case names of
742− [] -> return $ throw SqlError {
743− sqlNativeError = -1,
744− sqlErrorMsg = "invalid type oid",
745− sqlState = ""
746− }
747− [Only x] -> return x
748− _ -> fail "typename query returned more than one result"
749− -- oid is a primary key, so the query should
750− -- never return more than one result
751− return (IntMap.insert (oid2int oid) name oidmap, name)