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haskellyesodhaskell-persistent

How to find out which key is conflicting when using the replaceUnique method?

I'm using the replaceUnique method, which has return type of ReaderT backend m (Maybe (Unique record)). My database table has two unique fields and if uniqueness is violated, I want to find out which key is conflicting. How can I do that?

Solution

  • This can be achieved with this code:

    case unique of
  UniqueEmail _ -> -- email is conflicting
  UniqueDisplayName _ -> -- displayName is conflicting

    where unique is Unique record and UniqueEmail _ and UniqueDisplayName _ are uniqueness constraints.