This package helps you build administrative CRUD operations (Create, Retrieve, Update, Delete) into your web site, as Yesod subsites. There is a demo site in the example directory in the distribution.

To begin, add subsites to your routes file, like these:

/users         UserCrudR  CrudSubsite-UserCrud  mkUserCrud
/pubs/#UserId  PubCrudR   CrudSubsite-PubCrud   mkPubCrud

Now, in your Foundation module, you must define the subsite foundation types and functions. Here we have one foundation type that is nullary, and another that carries a piece of data.

data UserCrud = UserCrud
mkUserCrud :: a -> CrudSubsite UserCrud
mkUserCrud _ = CrudSubsite UserCrud

data PubCrud = PubCrud UserId
mkPubCrud :: a -> UserId -> CrudSubsite PubCrud
mkPubCrud _ = CrudSubsite . PubCrud

Next, define the type families on which these will operate. The simplest case is that ObjId is a Persistent database Key and Obj is one of your model types, but yesod-crud supports other types and non-Persistent databases too.

instance CrudTypes UserCrud where
  type Site UserCrud = App
  type ObjId UserCrud = UserId
  type Obj UserCrud = User

instance CrudTypes PubCrud where
  type Site PubCrud = App
  type ObjId PubCrud = PublicationId
  type Obj PubCrud = Publication

The above generally must go within the Foundation.hs of a scaffolded site, because it relies on the App type, and is in turn used in the routes file. The remaining CRUD operations can be defined elsewhere and then imported into Application.hs for the dispatcher to access.

instance RenderMessage (CrudSubsite UserCrud) CrudMessage where
  renderMessage _ _ CrudMsgEntity = "User"
  renderMessage _ _ CrudMsgEntities = "Users"
  renderMessage _ _ m = defaultCrudMessage m

instance Crud UserCrud where
  crudDB = return crudPersistDefaults
  crudShow = return . userIdent
  crudEq u v = return $ u == v
  crudMakeForm uOpt =
    return $ renderDivs $ User
    <$> areq textField "User name" (userIdent <$> uOpt)
    <*> aopt passwordField "Password" (userPassword <$> uOpt)

The minimal definition above will provide pages to list users, add a new user, update existing users, and delete users (with a confirmation step). Various aspects of the look and functionality can be overridden, and the CRUD widgets can be mixed and matched on other pages too.

Comments and critiques are welcome. Please use the Issues feature at https://github.com/league/yesod-crud