yesod how to show the pure value of a PersistInt64 key

Question

Dog
    name Text
    race Text

getAllDogsR :: Handler Html
getAllDogsR = do
    Dogs<- runDB $ selectList [] [Asc DogName]
    defaultLayout
        [whamlet|
            <ul>
                $forall Entity dogid dog <- Dogs
                    <li>
                        #{show $ unKey (dogid)}
       |]

When I run this code I will get a list of all dog keys that are in my database
like this:

PersistInt64 1
PersistInt64 2
PersistInt64 3
PersistInt64 4
etc

but what I actually want is to show the pure value of the key
like this:

1
2
3
4
etc

My question is how can I achieve this.

Does `#{case dogid of PersistInt64 x -> show $ unKey x}` work? — Ry-, Nov 08 '13 at 14:56
The function you want is [fromPersistValueText](http://hackage.haskell.org/package/persistent-1.2.3.0/docs/Database-Persist-Types.html#v:fromPersistValueText). However you can also have `module Model.Id` for anchors, ids and things like that. The module will contain class for id rendering: `class PersistId a where persistId :: Key a -> Text` and a couple of instances: `instance PersistId Dog where persistId = either T.pack id . fromPersistValueText . unKey` will do that you want. I think this will be convenient enough. — Samvel Truzyan, Nov 09 '13 at 04:40
Although you have asked how to print out the IDs as plain text, I suspect you are actually just going to print out the IDs to the user. If you eventually want to use those IDs in a URL, you can do so without any conversion: ` #{dogName dog} ` — Ecognium, Nov 09 '13 at 18:17

score 2 · Answer 1 · answered Nov 22 '13 at 11:00

You need to extract the key out of a KeyBackend first, like so:

extractKey :: KeyBackend backend entity -> String
extractKey = extractKey' . unKey
  where extractKey' (PersistInt64 k) = show k
        extractKey' _ = ""

You should now be able to do

#{extractKey dogid}

user316146 · Answer 2 · 2014-04-07T01:16:42.727

2

Change

#{show $ unKey (dogid)}

to

#{toPathPiece dogid}

edited Apr 07 '14 at 01:16

answered Apr 06 '14 at 23:18

user316146

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It would help if you could provide a more detailed answer with a working example, and possibly some contextual explanation. A one line comment is more suited as just that - a comment on the question. – Alex Osborn Apr 07 '14 at 00:22
@AlexOsborn: It isn't just a comment, though. It's an answer. It does exactly what he's asking for. – user316146 Apr 07 '14 at 01:18
`toPathPiece` is defined in the `path-pieces` package (http://hackage.haskell.org/package/path-pieces), in the `Web.PathPieces` module. If you have a `(Key x)` you can use `toPathPiece x`. – stusmith Apr 29 '14 at 19:57

yesod how to show the pure value of a PersistInt64 key

2 Answers2