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47 lines
1.6 KiB
Haskell
47 lines
1.6 KiB
Haskell
-- | Classes for monads used during schema construction and query parsing.
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module Hasura.GraphQL.Parser.Class.Parse where
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import Hasura.Prelude
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import Data.Parser.JSONPath
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import Hasura.Base.Error
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-- | A class that provides functionality for parsing GraphQL queries, i.e.
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-- running a fully-constructed 'Parser'.
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class Monad m => MonadParse m where
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withPath :: (JSONPath -> JSONPath) -> m a -> m a
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-- | Not the full power of 'MonadError' because parse errors cannot be
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-- caught.
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parseErrorWith :: Code -> Text -> m a
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-- | See 'QueryReusability'.
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markNotReusable :: m ()
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parseError :: MonadParse m => Text -> m a
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parseError = parseErrorWith ValidationFailed
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-- | Tracks whether or not a query is /reusable/. Reusable queries are nice,
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-- since we can cache their resolved ASTs and avoid re-resolving them if we
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-- receive an identical query. However, we can’t always safely reuse queries if
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-- they have variables, since some variable values can affect the generated SQL.
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-- For example, consider the following query:
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--
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-- > query users_where($condition: users_bool_exp!) {
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-- > users(where: $condition) {
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-- > id
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-- > }
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-- > }
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--
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-- Different values for @$condition@ will produce completely different queries,
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-- so we can’t reuse its plan (unless the variable values were also all
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-- identical, of course, but we don’t bother caching those).
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data QueryReusability = Reusable | NotReusable
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instance Semigroup QueryReusability where
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NotReusable <> _ = NotReusable
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_ <> NotReusable = NotReusable
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Reusable <> Reusable = Reusable
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instance Monoid QueryReusability where
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mempty = Reusable
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