haskell - use runDB in a SubSite Yesod -

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i want create post method in subsite create new entity, have aform

demoform :: rendermessage master formmessage => maybe demo -> aform    (handlert master io) demo demoform   demo = demo              <$> areq textfield (fieldsettingslabel ("fieldone"::t.text))   (demofieldone <$> demo)             <*> areq intfield  (fieldsettingslabel ("fieldone"::t.text))   (demofieldtwo <$> demo)             <*> areq boolfield (fieldsettingslabel ("fieldthree"::t.text)) (demofieldthree <$> demo)              <*> areq dayfield  (fieldsettingslabel ("fieldfour"::t.text))  (demofieldfour <$> demo)

and post method:

   postdemonewr :: (yesod master,rendermessage master formmessage) => handlert democrud (handlert master io) html    postdemonewr =             tp <- getroutetoparent              ((result,widget), encoding) <- lift $ runformpost $ renderbootstrap3 bootstrapbasicform $ demoform  nothing             case result of                  formsuccess demo ->                               _ <- lift $  rundb $ insert demo                              redirect demonewr                  _ -> lift $ defaultlayout $                  let actionr = demonewr                                  [whamlet|                     <form method=post action=@{tp demonewr} enctype=#{encoding}>                           ^{widget}                     <button .btn .btn-default> default text create                |]

but have following error

  not deduce (yesodpersistbackend master                   ~ persistent-2.1.3:database.persist.sql.types.sqlbackend) context (yesod master, rendermessage master formmessage)   bound type signature              postdemonewr :: (yesod master, rendermessage master formmessage) =>

i thing need add yesodpersist i'm not sure how

you need add following constraint postdemonewr declaration:

yesodpersist master => yesodpersistbackend master ~ sqlbackend => …

the first constraint tells master must have persistent abilities while second constraint tells backend used persistent should sql backend.

you can find similar in other question


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