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39 lines
1.1 KiB
Haskell
39 lines
1.1 KiB
Haskell
module Hasura.SQL.Backend
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( BackendType(..)
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, supportedBackends
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) where
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import Hasura.Prelude
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import Data.Aeson
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import Data.Text (unpack)
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import Data.Text.Extended
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-- | An enum that represents each backend we support.
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-- This type MUST be an enumeration (an enumeration consists of one or
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-- more nullary, non-GADT constructors).
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data BackendType
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= Postgres
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| MSSQL
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deriving (Eq, Ord, Bounded, Enum)
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-- | The name of the backend, as we expect it to appear in our metadata and API.
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instance ToTxt BackendType where
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toTxt Postgres = "postgres"
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toTxt MSSQL = "mssql"
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-- | The FromJSON instance uses this lookup mechanism to avoid having
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-- to duplicate and hardcode the backend string.
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instance FromJSON BackendType where
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parseJSON = withText "backend type" \name ->
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lookup name [(toTxt b, b) | b <- supportedBackends]
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`onNothing` fail ("got: " <> unpack name <> ", expected one of: " <> unpack (commaSeparated supportedBackends))
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instance ToJSON BackendType where
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toJSON = String . toTxt
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supportedBackends :: [BackendType]
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supportedBackends = [minBound @BackendType .. maxBound]
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