graphql/Data/GraphQL/Execute.hs

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{-# LANGUAGE CPP #-}
-- | This module provides the function to execute a @GraphQL@ request --
-- according to a 'Schema'.
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module Data.GraphQL.Execute (execute) where
#if !MIN_VERSION_base(4,8,0)
import Control.Applicative ((<$>))
#endif
import Control.Applicative (Alternative)
import Data.Maybe (catMaybes)
import qualified Data.Aeson as Aeson
import Data.GraphQL.AST
import Data.GraphQL.Schema (Schema(..))
import qualified Data.GraphQL.Schema as Schema
import Data.GraphQL.Error
-- | Takes a 'Schema', a variable substitution function ('Schema.Subs'), and a
-- @GraphQL@ 'document'. The substitution is applied to the document using
-- 'rootFields', and the 'Schema''s resolvers are applied to the resulting fields.
--
-- Returns the result of the query against the 'Schema' wrapped in a /data/ field, or
-- errors wrapped in an /errors/ field.
execute :: Alternative f
=> Schema.Schema f -> Schema.Subs -> Document -> f Aeson.Value
execute (Schema resolvs) subs doc = runCollectErrs res
where res = Schema.resolvers resolvs $ rootFields subs doc
-- | Takes a variable substitution function and a @GraphQL@ document.
-- If the document contains one query (and no other definitions)
-- it applies the substitution to the query's set of selections
-- and then returns their fields.
rootFields :: Schema.Subs -> Document -> [Field]
rootFields subs (Document [DefinitionOperation (Query (Node _varDefs _ _ sels))]) =
Schema.fields $ substitute subs <$> sels
rootFields _ _ = []
-- | Takes a variable substitution function and a selection. If the
-- selection is a field it applies the substitution to the field's
-- arguments using 'subsArg', and recursively applies the substitution to
-- the arguments of fields nested in the primary field.
substitute :: Schema.Subs -> Selection -> Selection
substitute subs (SelectionField (Field alias name args directives sels)) =
SelectionField $ Field
alias
name
-- TODO: Get rid of `catMaybes`, invalid arguments should raise an error
(catMaybes $ subsArg subs <$> args)
directives
(substitute subs <$> sels)
substitute _ sel = sel
-- TODO: Support different value types
-- | Takes a variable substitution function and an argument. If the
-- argument's value is a variable the substitution is applied to the
-- variable's name.
subsArg :: Schema.Subs -> Argument -> Maybe Argument
subsArg subs (Argument n (ValueVariable (Variable v))) =
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Argument n . ValueString <$> subs v
subsArg _ arg = Just arg