postgresql-simple 0.3.0.0 → 0.3.0.1

raw patch · 2 files changed

+57/−57 lines, 2 files

Files

• postgresql-simple.cabal +2/−2
• src/Database/PostgreSQL/Simple/FromField.hs +55/−55

@@ -1,5 +1,5 @@ Name:                postgresql-simple-Version:             0.3.0.0+Version:             0.3.0.1 Synopsis:            Mid-Level PostgreSQL client library Description:     Mid-Level PostgreSQL client library, forked from mysql-simple.@@ -72,7 +72,7 @@ source-repository this   type:     git   location: http://github.com/lpsmith/postgresql-simple-  tag:      v0.3.0.0+  tag:      v0.3.0.1  test-suite test   type:           exitcode-stdio-1.0

@@ -3,61 +3,61 @@ {-# LANGUAGE PatternGuards, ScopedTypeVariables      #-} {-# LANGUAGE RecordWildCards                         #-} ---------------------------------------------------------------------------------- |--- Module:      Database.PostgreSQL.Simple.FromField--- Copyright:   (c) 2011 MailRank, Inc.---              (c) 2011-2012 Leon P Smith--- License:     BSD3--- Maintainer:  Leon P Smith <leon@melding-monads.com>--- Stability:   experimental--- Portability: portable------ The 'FromField' 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--- PostgreSQL numeric types that are less accurate than it. For instance,--- the Haskell 'Double' type is compatible with the PostgreSQL's 32-bit--- @int@ type because it can represent a @int@ exactly.  On the other hand,--- since a 'Double' might lose precision if representing PostgreSQL's 64-bit--- @bigint@, the two are /not/ considered compatible.------ Because 'FromField' is a typeclass,  one may provide conversions to--- additional Haskell types without modifying postgresql-simple.  This is--- particularly useful for supporting PostgreSQL types that postgresql-simple--- does not support out-of-box.  Here's an example of what such an instance--- might look like for a UUID type that implements the @Read@ class:------ @--- import Data.UUID ( UUID )--- import Database.PostgreSQL.Simple.BuiltinTypes---                  ( BuiltinType(UUID), builtin2oid )--- import qualified Data.ByteString as B------ instance FromField UUID where---    fromField f mdata =---        if typeOid f /= builtin2oid UUID---        then returnError Incompatible f ""---        else case B.unpack `fmap` mdata of---               Nothing   -> returnError UnexpectedNull f ""---               Just data ->---                   case [ x | (x,t) <- reads data, ("","") <- lex t ] of---                     [x] -> Ok x---                     _   -> returnError ConversionError f data--- @------ Note that because PostgreSQL's @uuid@ type is built into postgres and is--- not provided by an extension,  the 'typeOid' of @uuid@ does not change and--- thus we can examine it directly.   Here,  we simply pull the type oid out--- of the static table provided by postgresql-simple.------ On the other hand if the type is provided by an extension,  such as--- @PostGIS@ or @hstore@,  then the 'typeOid' is not stable and can vary from--- database to database. In this case it is recommended that FromField--- instances use 'typename' instead.----------------------------------------------------------------------------------+{- |+Module:      Database.PostgreSQL.Simple.FromField+Copyright:   (c) 2011 MailRank, Inc.+             (c) 2011-2012 Leon P Smith+License:     BSD3+Maintainer:  Leon P Smith <leon@melding-monads.com>+Stability:   experimental+Portability: portable++The 'FromField' 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+PostgreSQL numeric types that are less accurate than it. For instance,+the Haskell 'Double' type is compatible with the PostgreSQL's 32-bit+@int@ type because it can represent a @int@ exactly.  On the other hand,+since a 'Double' might lose precision if representing PostgreSQL's 64-bit+@bigint@, the two are /not/ considered compatible.++Because 'FromField' is a typeclass,  one may provide conversions to+additional Haskell types without modifying postgresql-simple.  This is+particularly useful for supporting PostgreSQL types that postgresql-simple+does not support out-of-box.  Here's an example of what such an instance+might look like for a UUID type that implements the @Read@ class:++@+import Data.UUID ( UUID )+import Database.PostgreSQL.Simple.BuiltinTypes+                 ( BuiltinType(UUID), builtin2oid )+import qualified Data.ByteString as B++instance FromField UUID where+   fromField f mdata =+      if typeOid f /= builtin2oid UUID+        then returnError Incompatible f \"\"+        else case B.unpack \`fmap\` mdata of+               Nothing   -> returnError UnexpectedNull f \"\"+               Just data ->+                  case [ x | (x,t) <- reads data, (\"\",\"\") <- lex t ] of+                    [x] -> Ok x+                    _   -> returnError ConversionError f data+@++Note that because PostgreSQL's @uuid@ type is built into postgres and is+not provided by an extension,  the 'typeOid' of @uuid@ does not change and+thus we can examine it directly.   Here,  we simply pull the type oid out+of the static table provided by postgresql-simple.++On the other hand if the type is provided by an extension,  such as+@PostGIS@ or @hstore@,  then the 'typeOid' is not stable and can vary from+database to database. In this case it is recommended that FromField+instances use 'typename' instead.++-}+  module Database.PostgreSQL.Simple.FromField     (