examples/CustomTupleable.hs · project-m36

git.iko.soy/project-m36

project-m36/examples/CustomTupleable.hs

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1{-# LANGUAGE DeriveGeneric, OverloadedStrings #-}

2--this example shows how to implement a non-generics-defined Tupleable instance which is required in scenarios where Haskell-side types are not supported server-side or where one wishes to represent a nested relation

3import ProjectM36.Client

4import ProjectM36.Tuple

5import ProjectM36.Tupleable

6import ProjectM36.Relation

7import ProjectM36.Atom

8import ProjectM36.Attribute as A

9import qualified Data.Set as S

10import qualified Data.Map as M

11import Data.Text (Text)

12import GHC.Generics

13import Data.Proxy

15--in this contrived example, we wish to represent one relation with a nested relation of comments

16data Blog = Blog {

17 title :: Text,

18 comments :: S.Set Comment

19 } deriving (Show)

21data Comment = Comment {

22 authorName :: Text,

23 comment :: Text

24 } deriving (Eq, Show, Generic, Ord)

26instance Tupleable Comment

28instance Tupleable Blog where

29 toTuple blogentry =

30 mkRelationTupleFromMap (M.fromList [("title", TextAtom (title blogentry)),

31 ("comments", RelationAtom relFromComments)])

32 where

33 commentTuples = map toTuple (S.toList (comments blogentry))

34 relFromComments = case mkRelationFromTuples (toAttributes (Proxy :: Proxy Comment)) commentTuples of

35 Left err -> error (show err)

36 Right rel -> rel

38 fromTuple tupIn = do

39 titleAtom <- atomForAttributeName "title" tupIn

40 commentsAtom <- atomForAttributeName "comments" tupIn

41 commentsRel <- relationForAtom commentsAtom

42 comments' <- mapM fromTuple (tuplesList commentsRel)

43 pure Blog {

44 title = atomToText titleAtom,

45 comments = S.fromList comments'}

47 toAttributes _ = A.attributesFromList [Attribute "title" TextAtomType,

48 Attribute "comments" $ RelationAtomType (toAttributes (Proxy :: Proxy Comment))]