这里有两种方法具有相同的结果类型:
- 新类型化的SQL的基础上,从菲利普·莱萨的“esqueleto”包,它是持久的基础
和以前rawSql方式
只需加1或2作为参数
对于定界符quasiquoter
{- file prova.hs-}
{-# LANGUAGE QuasiQuotes, TemplateHaskell, TypeFamilies, OverloadedStrings #-}
{-# LANGUAGE GADTs, FlexibleContexts, ConstraintKinds, ScopedTypeVariables #-}
import Prelude hiding (catch)
import Control.Exception
import Database.Persist
import Database.Persist.Sqlite
import Database.Persist.TH
import Control.Monad.IO.Class (liftIO)
import Data.Text (Text)
import Database.Persist.Quasi
import Database.Esqueleto as Esql
import Database.Persist.GenericSql (SqlPersist, rawSql)
import Control.Monad.Logger (MonadLogger)
import Control.Monad.Trans.Resource (MonadResourceBase)
import System.Environment (getProgName, getArgs)
import System.Exit (exitSuccess, exitWith, ExitCode(..))
import Text.Printf (printf)
import QQStr(str) -- heredoc quasiquoter module
share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persist|
Person
number Int
numberOfEyes Int
firstName FirstnamesId
lastName LastnamesId
UniquePersonNumber number
deriving Show
Lastnames
lastname String
deriving Show
Firstnames
firstname String
deriving Show
|]
-- the esqueleto way
-- with this type annotation it could be run in a yesod handler with ''runDB''
getPersonInfoByNumber :: (PersistQuery SqlPersist m, MonadLogger m, MonadResourceBase m) => Int -> SqlPersist m (Maybe (Int, String, String))
getPersonInfoByNumber pNumber = do
result <- select $ from $ \(fn `InnerJoin` p `InnerJoin` ln) -> do
on ((p ^. PersonFirstName) Esql.==. (fn ^. FirstnamesId))
on ((p ^. PersonLastName) Esql.==. (ln ^. LastnamesId))
where_ ((p ^. PersonNumber) Esql.==. val pNumber)
return (p , fn, ln)
case result of
[(Entity _ p, Entity _ fn, Entity _ ln)] -> return $ Just (personNumberOfEyes p, firstnamesFirstname fn, lastnamesLastname ln)
_ -> return Nothing
-- the rawSql way
stmt = [str|SELECT ??, ??, ??
FROM Person, Lastnames, Firstnames
ON Person.firstName = Firstnames.id
AND Person.lastName = Lastnames.id
WHERE Person.number = ?
|]
getPersonInfoByNumberRaw :: (PersistQuery SqlPersist m, MonadLogger m, MonadResourceBase m) => Int -> SqlPersist m (Maybe (Int, String, String))
getPersonInfoByNumberRaw pNumber = do
result <- rawSql stmt [toPersistValue pNumber]
case result of
[(Entity _ p, Entity _ fn, Entity _ ln)] -> return $ Just (personNumberOfEyes p, firstnamesFirstname fn, lastnamesLastname ln)
_ -> return Nothing
main :: IO()
main = do
args <- getArgs
nomProg <- getProgName
case args of
[] -> do
printf "%s: just specify 1 for esqueleto or 2 for rawSql.\n" nomProg
exitWith (ExitFailure 1)
[arg] -> (withSqliteConn ":memory:" $ runSqlConn $ do
runMigration migrateAll
let myNumber = 5
fnId <- insert $ Firstnames "John"
lnId <- insert $ Lastnames "Doe"
-- in case of insert collision, because of UniquePersonNumber constraint
-- insertUnique does not throw exceptions, returns success in a Maybe result
-- insert would throw an exception
maybePersId <- insertUnique $ Person {personNumber = myNumber, personNumberOfEyes=2,
personFirstName = fnId, personLastName = lnId}
info <- case arg of
"1" -> getPersonInfoByNumber myNumber
_ -> getPersonInfoByNumberRaw myNumber
liftIO $ putStrLn $ show info
)
`catch` (\(excep::SomeException) ->
putStrLn $ "AppSqlError: " ++ show excep)
额外的模块
module QQStr(str) where
import Prelude
import Language.Haskell.TH
import Language.Haskell.TH.Quote
str = QuasiQuoter { quoteExp = stringE, quotePat = undefined
, quoteType = undefined, quoteDec = undefined }
执行:
[email protected]:~/webs/yesod/prova$ ./cabal-dev/bin/prova 1
Migrating: CREATE TABLE "Person"("id" INTEGER PRIMARY KEY,"number" INTEGER NOT NULL,"numberOfEyes" INTEGER NOT NULL,"firstName" INTEGER NOT NULL REFERENCES "Firstnames","lastName" INTEGER NOT NULL REFERENCES "Lastnames")
Migrating: CREATE TABLE "Lastnames"("id" INTEGER PRIMARY KEY,"lastname" VARCHAR NOT NULL)
Migrating: CREATE TABLE "Firstnames"("id" INTEGER PRIMARY KEY,"firstname" VARCHAR NOT NULL)
Just (2,"John","Doe")
因为我已经从哈斯克尔移动了,但我会去的肢体,并认为这是不正确的测试。 :) – andreasm 2012-09-19 07:25:09