How to perform database queries in GHCi in Yesod Application

问题

How to, for example, insert a new User into a database using Yesod application's models? Or is there a better way?

I am dealing with scaffolded application. Now I created App instance and dont know how to perform requests using it.

:i Extra
data Extra
  = Extra {extraCopyright :: Data.Text.Internal.Text,
           extraAnalytics :: Maybe Data.Text.Internal.Text}
        -- Defined in `Settings

let e = Extra "asdf" Nothing
let c = AppConfig {appEnv = Development, appPort = 3000, appRoot = "/", appHost = "localhost", appExtra = e}
f <- makeFoundation c
:t f
f :: App

:i App
data App
  = App {settings :: AppConfig DefaultEnv Extra,
         getStatic :: Yesod.Static.Static,
         connPool :: persistent-1.2.3.0:Database.Persist.Class.PersistConfig.PersistConfigPool
                       PersistConf,
         httpManager :: http-client-0.2.0.1:Network.HTTP.Client.Types.Manager,
         persistConfig :: PersistConf,
         appLogger :: Yesod.Core.Types.Logger}
        -- Defined in `Foundation'

What next?

回答1:

If you just want to do Persistent queries in ghci you can do this without creating a Yesod application. Unfortunately doing this is differs quite a bit depending on the specific back end you want to use.

For SQLite:

> import Database.Persist.Sqlite
> import Model
> pool <- createSqlitePool "yesod-test.sqlite3" 2
> runSqlite "yesod-test.sqlite3" (runMigration migrateAll)
> userId <- runSqlite "yesod-test.sqlite3" (insert (User "foo@bar.com" Nothing))

For Postgresql:

-- In Shell: $ createdb yesod-test
> import Database.PostgreSQL.Simple
> con <- connectPostgreSQL  "dbname=yesod-test"
> import Database.Persist.Postgresql
> pcon <- openSimpleConn con
> import Model
> runSqlPersistM (runMigration migrateAll) pcon
> userId <- runSqlPersistM (insert (User "foo@bar.com" Nothing)) pcon
> Just user <- runSqlPersistM (get userId) pcon
> userIdent user

回答2:

The scaffolding provides (at least with yesod-bin 1.4.5) a function db in Application.hs which you can use:

$ cabal repl
...
*Application> db $ insert $ User "foo@bar.com" Nothing

来源：https://stackoverflow.com/questions/20968016/how-to-perform-database-queries-in-ghci-in-yesod-application

标签

haskell

yesod

persistent

ghci