CODEWITHSUNDEEP
haskellyesodpersistenthamlet
jpaugh
jpaugh

Reputation: 7035

How to combine "details" from a separate query in a list in Hamlet?

I'd like to display a list of items in a webpage, along with associated details from a separate table (with a many-to-one relationship). How do I do this in Yesod? I am using the default scaffolding. The upshot is that runDB cannot be nested in a WidgetT context — or so I think.

To make this more concrete, how do I define the function featuresAssociatedWith to use in the following hamlet code:

<h2> Cars

$forall Entity carId car <- carList
    <div class="car-item">
        <h3> #{carYear car}&nbsp;#{carMake car} #{carModel car}
        <ul>
            $forall feature <- featuresAssociatedWith carId
                <li> #{feature}

Given the following models:

Car
    make        Text
    model       Text
    year        Int

CarFeature
    car         CarId
    text        Text
    UniqueCF    car text

Here is the current handler function

getCarListR :: Handler Html
getCarListR = do
        carList <- runDB $ selectList [] [Asc CarOrder]
        liftIO $ print $ length carList
        defaultLayout $ do
            setTitle "Cars"
            $(widgetFile "carList")

It seems most natural to embed a runDB query in the Widget this way, but again, this isn't possible:

featuresAssocWith :: CarId -> [Entity CarFeature]
featuresAssocWith carID = selectList [CarFeatureCar ==. carID] []

Upvotes: 2

Views: 68

Answers (1)

Michael Snoyman
Michael Snoyman

Reputation: 31315

Hamlet is designed to not allow you to perform actions like database queries inside of it. Instead, you'll need to perform the query outside of hamlet, and then pass in a list of tuples of car info together with the data from the associated table.

Upvotes: 2

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