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Not in scope error when nesting table per class inheritance #994

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#1256
Closed
Not in scope error when nesting table per class inheritance#994
#1256
Milestone
2.13

Description

@tysonzero
tysonzero
opened on Dec 19, 2019

To encode sum types / subtyping I am attempting to use the table per class strategy, similar to the shared primary keys strategy.

However I am running into a very strange not in scope error when modeling nested inheritance:

The following works and seems to give me what I want (if a bit hacky):

Vehicle

Car
    vehicle VehicleId sql=id
    Primary vehicle

Bike
    vehicle VehicleId sql=id
    Primary vehicle

However it breaks when I append the following to the bottom:

Coupe
    car CarId sql=id
    Primary car

Sedan
    car CarId sql=id
    Primary car

With the following error:

    • Not in scope: type constructor or class ‘VehicleId’
    • In the quasi-quotation:
        [persistLowerCase|

This is with persistent-2.9.2 and persistent-template-2.6.0.

Activity

  1. tysonzero
    changed the title [-]Not in scope error when nesting table er class inheritance[/-] [+]Not in scope error when nesting table per class inheritance[/+] on Dec 19, 2019

  2. parsonsmatt commented on Dec 19, 2019

    @parsonsmatt
    parsonsmatt
    on Dec 19, 2019
    Collaborator

    There's a simpler case:

      Top

  Middle
    top     TopId sql=id
    Primary top

  Bottom
    middle  MiddleId sql=id
    Primary middle

    which fails with a similar "TopId not in scope" error. If I -ddump-splices, I get this output:

    Output is kinda large, sorry 

    λ ~/Projects/persistent/persistent-test/ master* stack ghci src/PersistentTestModelsInherit.hs

Using configuration for persistent-test:lib to load /home/matt/Projects/persistent/persistent-
test/src/PersistentTestModelsInherit.hs
persistent-test> configure (lib)
Configuring persistent-test-2.0.3.0...
persistent-test> initial-build-steps (lib)
Configuring GHCi with the following packages: persistent-test
GHCi, version 8.6.5: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/matt/.dotfiles/haskell/ghci.symlink
[1 of 2] Compiling Init             ( /home/matt/Projects/persistent/persistent-test/src/Init.
hs, interpreted )
[2 of 2] Compiling PersistentTestModels ( /home/matt/Projects/persistent/persistent-test/src/P
ersistentTestModelsInherit.hs, interpreted )

/home/matt/Projects/persistent/persistent-test/src/PersistentTestModelsInherit.hs:13:135: erro
r:
    • Not in scope: type constructor or class ‘TopId’
    • In the quasi-quotation:
        [persistUpperCase|
  Top

  Middle
    top     TopId sql=id
    Primary top

  Bottom
    middle  MiddleId sql=id
    Primary middle
|]
   |
13 | share [mkPersist persistSettings,  mkMigrate "testMigrate", mkDeleteCascade persistSettin
gs, mkSave "_ignoredSave"] [persistUpperCase|
   |
                                             ^...
Failed, one module loaded.
Loaded GHCi configuration from /tmp/haskell-stack-ghci/46874742/ghci-script
λ> :set -ddump-splices
λ> :r
[2 of 2] Compiling PersistentTestModels ( /home/matt/Projects/persistent/persistent-test/src/P
ersistentTestModelsInherit.hs, interpreted )
/home/matt/Projects/persistent/persistent-test/src/PersistentTestModelsInherit.hs:(13,135)-(23
,2): Splicing expression
    template-haskell-2.14.0.0:Language.Haskell.TH.Quote.quoteExp
      persistUpperCase
      "\n\
      \  Top\n\
      \\n\
      \  Middle\n\
      \    top     TopId sql=id\n\
      \    Primary top\n\
      \\n\
      \  Bottom\n\
      \    middle  MiddleId sql=id\n\
      \    Primary middle\n"
  ======>
    [((((((((((EntityDef (HaskellName (Data.Text.pack "Top")))
                (DBName (Data.Text.pack "Top")))
               ((((((((FieldDef (HaskellName (Data.Text.pack "Id")))
                        (DBName (Data.Text.pack "id")))
                       ((FTTypeCon Nothing) (Data.Text.pack "TopId")))
                      SqlInt64)
                     [])
                    True)
                   ((ForeignRef (HaskellName (Data.Text.pack "Top")))
                      ((FTTypeCon (Just (Data.Text.pack "Data.Int")))
                         (Data.Text.pack "Int64"))))
                  Nothing))
              [])
             [])
            [])
           [])
          [])
         (Data.Map.Internal.fromList []))
        False)
       Nothing
       {entityFields = [],
        entityId = (((((((FieldDef (HaskellName (Data.Text.pack "Id")))
                           (DBName (Data.Text.pack "id")))
                          ((FTTypeCon Nothing) (Data.Text.pack "TopId")))
                         (sqlType (Data.Proxy.Proxy :: Data.Proxy.Proxy Int64)))
                        [])
                       True)
                      ((ForeignRef (HaskellName (Data.Text.pack "Top")))
                         ((FTTypeCon (Just (Data.Text.pack "Data.Int")))
                            (Data.Text.pack "Int64"))))
                     Nothing},
     ((((((((((EntityDef (HaskellName (Data.Text.pack "Middle")))
                (DBName (Data.Text.pack "Middle")))
               ((((((((FieldDef (HaskellName (Data.Text.pack "Id")))
                        (DBName (Data.Text.pack "id")))
                       ((FTTypeCon Nothing) (Data.Text.pack "MiddleId")))
                      (SqlOther (Data.Text.pack "Primary Key")))
                     [])
                    True)
                   (CompositeRef
                      ((CompositeDef
                          [(((((((FieldDef (HaskellName (Data.Text.pack "top")))
                                   (DBName (Data.Text.pack "id")))
                                  ((FTTypeCon Nothing) (Data.Text.pack "TopId")))
                                 (SqlOther (Data.Text.pack "SqlType unset for top")))
                                [Data.Text.pack "sql=id"])
                               True)
                              NoReference)
                             Nothing])
                         [])))
                  Nothing))
              [])
             [(((((((FieldDef (HaskellName (Data.Text.pack "top")))
                      (DBName (Data.Text.pack "id")))
                     ((FTTypeCon Nothing) (Data.Text.pack "TopId")))
                    (SqlOther (Data.Text.pack "SqlType unset for top")))
                   [Data.Text.pack "sql=id"])
                  True)
                 ((ForeignRef (HaskellName (Data.Text.pack "Top")))
                    ((FTTypeCon (Just (Data.Text.pack "Data.Int")))
                       (Data.Text.pack "Int64"))))
                Nothing])
            [])
           [])
          [])
         (Data.Map.Internal.fromList []))
        False)
       Nothing
       {entityFields = [(((((((FieldDef
                                 (HaskellName (Data.Text.pack "top")))
                                (DBName (Data.Text.pack "id")))
                               ((FTTypeCon Nothing) (Data.Text.pack "TopId")))
                              (sqlType (Data.Proxy.Proxy :: Data.Proxy.Proxy Int64)))
                             [Data.Text.pack "sql=id"])
                            True)
                           ((ForeignRef (HaskellName (Data.Text.pack "Top")))
                              ((FTTypeCon (Just (Data.Text.pack "Data.Int")))
                                 (Data.Text.pack "Int64"))))
                          Nothing],
        entityId = (((((((FieldDef (HaskellName (Data.Text.pack "Id")))
                           (DBName (Data.Text.pack "id")))
                          ((FTTypeCon Nothing) (Data.Text.pack "MiddleId")))
                         (SqlOther (Data.Text.pack "Composite Reference")))
                        [])
                       True)
                      (CompositeRef
                         ((CompositeDef
                             [(((((((FieldDef (HaskellName (Data.Text.pack "top")))
                                      (DBName (Data.Text.pack "id")))
                                     ((FTTypeCon Nothing) (Data.Text.pack "TopId")))
                                    (SqlOther (Data.Text.pack "SqlType unset for top")))
                                   [Data.Text.pack "sql=id"])
                                  True)
                                 NoReference)
                                Nothing])
                            [])))
                     Nothing},
     ((((((((((EntityDef (HaskellName (Data.Text.pack "Bottom")))
                (DBName (Data.Text.pack "Bottom")))
               ((((((((FieldDef (HaskellName (Data.Text.pack "Id")))
                        (DBName (Data.Text.pack "id")))
                       ((FTTypeCon Nothing) (Data.Text.pack "BottomId")))
                      (SqlOther (Data.Text.pack "Primary Key")))
                     [])
                    True)
                   (CompositeRef
                      ((CompositeDef
                          [(((((((FieldDef (HaskellName (Data.Text.pack "middle")))
                                   (DBName (Data.Text.pack "id")))
                                  ((FTTypeCon Nothing) (Data.Text.pack "MiddleId")))
                                 (SqlOther (Data.Text.pack "SqlType unset for middle")))
                                [Data.Text.pack "sql=id"])
                               True)
                              NoReference)
                             Nothing])
                         [])))
                  Nothing))
              [])
             [(((((((FieldDef (HaskellName (Data.Text.pack "middle")))
                      (DBName (Data.Text.pack "id")))
                     ((FTTypeCon Nothing) (Data.Text.pack "MiddleId")))
                    (SqlOther (Data.Text.pack "SqlType unset for middle")))
                   [Data.Text.pack "sql=id"])
                  True)
                 ((ForeignRef (HaskellName (Data.Text.pack "Middle")))
                    ((FTTypeCon (Just (Data.Text.pack "Data.Int")))
                       (Data.Text.pack "Int64"))))
                Nothing])
            [])
           [])
          [])
         (Data.Map.Internal.fromList []))
        False)
       Nothing
       {entityFields = [(((((((FieldDef
                                 (HaskellName (Data.Text.pack "middle")))
                                (DBName (Data.Text.pack "id")))
                               ((FTTypeCon Nothing) (Data.Text.pack "MiddleId")))
                              (sqlType (Data.Proxy.Proxy :: Data.Proxy.Proxy TopId)))
                             [Data.Text.pack "sql=id"])
                            True)
                           ((ForeignRef (HaskellName (Data.Text.pack "Middle")))
                              ((FTTypeCon (Just (Data.Text.pack "Data.Int")))
                                 (Data.Text.pack "Int64"))))
                          Nothing],
        entityId = (((((((FieldDef (HaskellName (Data.Text.pack "Id")))
                           (DBName (Data.Text.pack "id")))
                          ((FTTypeCon Nothing) (Data.Text.pack "BottomId")))
                         (SqlOther (Data.Text.pack "Composite Reference")))
                        [])
                       True)
                      (CompositeRef
                         ((CompositeDef
                             [(((((((FieldDef (HaskellName (Data.Text.pack "middle")))
                                      (DBName (Data.Text.pack "id")))
                                     ((FTTypeCon Nothing) (Data.Text.pack "MiddleId")))
                                    (SqlOther (Data.Text.pack "SqlType unset for middle")))
                                   [Data.Text.pack "sql=id"])
                                  True)
                                 NoReference)
                                Nothing])
                            [])))
                     Nothing}]

    The problem is in the Bottom { entityFields = ... } entry.

    -- Bottom:
       {entityFields = [(((((((FieldDef
                                 (HaskellName (Data.Text.pack "middle")))
                                (DBName (Data.Text.pack "id")))
                               ((FTTypeCon Nothing) (Data.Text.pack "MiddleId")))
                                                                    -- vvvvvvvvvvvv
                              (sqlType (Data.Proxy.Proxy :: Data.Proxy.Proxy TopId)))
                                                                    -- ^^^^^^^^^^^^
                             [Data.Text.pack "sql=id"])
                            True)
                           ((ForeignRef (HaskellName (Data.Text.pack "Middle")))
                              ((FTTypeCon (Just (Data.Text.pack "Data.Int")))
                                 (Data.Text.pack "Int64"))))
                          Nothing],

-- Middle:
       {entityFields = [(((((((FieldDef
                                 (HaskellName (Data.Text.pack "top")))
                                (DBName (Data.Text.pack "id")))
                               ((FTTypeCon Nothing) (Data.Text.pack "TopId")))
                                                                    -- vvvvvvvvvvvv
                              (sqlType (Data.Proxy.Proxy :: Data.Proxy.Proxy Int64)))
                                                                    -- ^^^^^^^^^^^^
                             [Data.Text.pack "sql=id"])
                            True)
                           ((ForeignRef (HaskellName (Data.Text.pack "Top")))
                              ((FTTypeCon (Just (Data.Text.pack "Data.Int")))
                                 (Data.Text.pack "Int64"))))
                          Nothing],

    TopId is being referenced directly here for some reason, instead of a Proxy Int64 and it'll be set later by the TH machinery. So that's not right!

    The ForeignRef stuff is fine, it's just the FieldDef that is wrong.

    Cleaning up the Middle, we get:

        { entityFields = 
        [ FieldDef 
            (HaskellName "top") 
            (DBName "id") 
            ((FTTypeCon Nothing) "TopId") 
            (sqlType (Data.Proxy.Proxy :: Data.Proxy.Proxy Int64)) 
            [Data.Text.pack "sql=id"] 
            True 
            (ForeignRef (HaskellName "Top") ((FTTypeCon (Just "Data.Int")) "Int64")) 
            Nothing
        ]
    }

    While Bottom has this:

        { entityFields = 
        [ FieldDef 
            (HaskellName "middle") 
            (DBName "id") 
            (FTTypeCon Nothing "MiddleId") 
            (sqlType (Data.Proxy.Proxy :: Data.Proxy.Proxy TopId)) 
            [Data.Text.pack "sql=id"] 
            True 
            (ForeignRef (HaskellName "Middle") ((FTTypeCon (Just "Data.Int")) "Int64")) 
            Nothing
        ]

    So the problem is very specifically when the QuasiQuoter is looking up the field type. Something is properly setting the Proxy :: Proxy (TopId -> Int64) in the .Quasi module, but I can't really tell what.

  3. parsonsmatt
    closed this as completedon Dec 19, 2019
  4. parsonsmatt
    reopened this on Dec 19, 2019

  5. tysonzero commented on Feb 11, 2020

    @tysonzero
    tysonzero
    on Feb 11, 2020
    Author

    @parsonsmatt

    Any thoughts on where to go from here? I'm happy to help, although I admittedly know very little about Template Haskell and quasi quotes.

    We are trying to move toward table per class inheritance due to the significant issues with our current approximation of it (lots of joins, extra error possibilities, significantly more key-passing noise). This approach is currently the only way to implement table per class inheritance in persistent.

  6. parsonsmatt commented on Feb 14, 2020

    @parsonsmatt
    parsonsmatt
    on Feb 14, 2020
    Collaborator

    #1042 is a conglomerate issue to track failures of key/id lookups

  7. parsonsmatt
    added this to the 2.13 milestone on May 4, 2021
  8. parsonsmatt
    linked a pull request that will close this issueQuasiQuoter Improvements #1256on May 4, 2021
  9. parsonsmatt
    closed this as completedon May 4, 2021
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