Writing Yesod test case for handler with an id parameter, where id is a key to an Entity

Question

I have been following the yesod tutorial and I am stuck on how to build a unit test involving parameters in a view that also hit a database. Backtracking a little, I followed the Echo.hs example:

    getEchoR :: Text -> Handler Html
    getEchoR theText = do
        defaultLayout $ do
            $(widgetFile "echo")

The corresponding test, note I have to cast the parameter into Text using Data.Text.pack

    yit "Echo some text" $ do
        get $ EchoR $ pack "Hello"
        statusIs 200

Now I have the model defined like so:

Tag
    name Text
    type Text

With a handler that can render that that obviously take a TagId as the parameter

    getTagR :: TagId -> Handler Html
    getTagR tagId = do
        tag <- runDB $ get404 tagId
        defaultLayout $ do
            setTitle $ toHtml $ tagName tag
            $(widgetFile "tag")

This is where the test fails.

    yit "Get a tag" $ do
        -- tagId is undefined
        get $ TagR tagId
        statusIs 200

I am not sure how to define the tagId. It wouldn't work with a String or Text or Num, and I can't seem to figure out how to generate one as I can't find any example code in various Data.Persist tutorials. Or better yet, some other way to call the get method.

Answer 1

You want to use the Key data constructor to construct an ID value, which takes a PersistValue as a parameter. A simple example of creating one is:

Key $ PersistInt64 5

Another option is to call get with a textual URL, e.g. get ("/tag/5" :: Text).

Answer 2

Since times have changed, I'll leave this note here to say that these days one would use something like:

fromBackendKey 5

See the docs for fromBackendKey.