我正在尝试学习持久库。
我有两个文件，其中一个包含我为项目定义的所有类型（饮食跟踪器）
Report.hs
data FoodEntry = FoodEntry { report :: Report
, date :: UTCTime
}
data Report = Report { ...
...
}
和另一个用于生成表格的文件
Storage.hs
import Database.Persist.Sql
import qualified Database.Persist.TH as PTH
PTH.share [ PTH.mkPersist PTH.sqlSettings
, PTH.mkMigrate "migrateAll"
]
[PTH.persistLowerCase|
FoodEntry sql=entries
report Report
date UTCTime default=now()
UniqueDate date
Report sql=reports
name Text
reportingUnit Text
nutrients [Nutrient]
Nutrient sql=nutrients
nutrientName Text
nutrientUnit Text
nutrientValue Double Maybe
deriving Show Read
|]
和一个处理迁移的文件
import Control.Monad.Logger
import Database.Persist
import Database.Persist.Postgresql
import Types.Storage
connString :: ConnectionString
connString = "host=127.0.0.1 port=5432 user=postgres dbname=postgres password=password"
runAction
:: (MonadUnliftIO m, IsPersistBackend r,
BaseBackend r ~ SqlBackend) =>
ConnectionString -> ReaderT r (LoggingT m) a -> m a
runAction connectionString action = runStdoutLoggingT
$ withPostgresqlConn connectionString
$ \backend ->
runReaderT action backend
migrateDB :: IO ()
migrateDB = runAction connString (runMigration migrateAll)
在我调用的[ProjectName.hs]文件中main
args <- parseArgs -- args - optparse-applicative
if generateDB args == Just True
then migrateDB
else case (...) of
... -> ...
... -> ...
(s, n, p, Just True) -> undefined
对于最后一种情况，我想将用户条目添加到数据库中。
我还有一个使用searchReport, s&n来p返回Report类型的函数。
我想做这样的事情
insertReport :: (MonadIO m) => UTCTime -> Report -> SqlPersistT m (Key FoodEntry)
insertReport time report' = insert (FoodEntry report' time)
do date' <- Data.Time.Clock.getCurrentTime :: IO UTCTime
report' <- searchReport s n p :: IO Report
insertReport $ date' report'
但是（AFAIK）有两个问题
的类型与我可以编写一个将一个转换为另一个的函数
Report.FoodEntry的类型不匹配，Storage.FoodEntry但我想知道是否有更好的方法来做到这一点。如果我要像这样测试那个 do 块中的函数
(s, n, p, Just True) -> insertReport undefined undefined我收到错误
• Couldn't match type ‘ReaderT Database.Persist.Sql.Types.Internal.SqlBackend m0’ with ‘IO’ Expected type: IO () Actual type: persistent-2.9.2:Database.Persist.Sql.Types.SqlPersistT m0 (persistent-2.9.2:Database.Persist.Class.PersistEntity.Key Types.Storage.FoodEntry)