Haskell Esqueleto 3表联接

Question

这些是我尝试从三个表进行SELECT的尝试。 但是它们不编译，而且我不理解该错误（我不知道为什么它期望一个元组(Entity Issue, b0)而不是我认为代码尝试获取的三元组）。

尝试1：

{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE TypeFamilies #-}

module Handler.Support where

import           Import hiding ((==.))
import qualified Database.Esqueleto as E
import           Database.Esqueleto      ((^.), (==.), (&&.))
import           Data.Traversable

getSupportR :: CustomerId -> Handler Html
getSupportR customerId = do
  customer_issues_followUps_list <- runDB $
    E.select $
    E.from $ \(i, f, c) -> do
    E.where_ (i ^. IssueCustomerId ==. E.val customerId &&. i ^. IssueId ==. f ^. FollowUpIssueId &&. i ^. IssueCustomerId ==. c ^. CustomerId)
    return (i, f, c)
  let issues = map listToMaybe . group . sort . fst . unzip $ customer_issues_followUps_list
  defaultLayout $ do
    setTitle "Your Licenses"
    $(widgetFile "support-display")

错误1：

/home/hhefesto/dev/laurus-nobilis/src/Handler/Support.hs:41:5: error:
    • Couldn't match type ‘(ra, rb, rc)’ with ‘(Entity Issue, b0)’
        arising from a functional dependency between:
          constraint ‘Database.Esqueleto.Internal.Sql.SqlSelect
                        (E.SqlExpr (Entity Issue), E.SqlExpr (Entity FollowUp),
                         E.SqlExpr (Entity Customer))
                        (Entity Issue, b0)’
            arising from a use of ‘E.select’
          instance ‘Database.Esqueleto.Internal.Sql.SqlSelect
                      (a3, b3, c) (ra3, rb3, rc3)’
            at <no location info>
    • In the second argument of ‘($)’, namely
        ‘E.select
           $ E.from
               $ \ (i, f, c)
                   -> do E.where_
                           (i ^. IssueCustomerId ==. E.val customerId
                              &&.
                                i ^. IssueId ==. f ^. FollowUpIssueId
                                  &&. i ^. IssueCustomerId ==. c ^. CustomerId)
                         return (i, f, c)’
      In a stmt of a 'do' block:
        customer_issues_followUps_list <- runDB
                                            $ E.select
                                                $ E.from
                                                    $ \ (i, f, c)
                                                        -> do E.where_
                                                                (i ^. IssueCustomerId
                                                                   ==. E.val customerId
                                                                   &&.
                                                                     i ^. IssueId
                                                                       ==. f ^. FollowUpIssueId
                                                                       &&.
                                                                         i ^. IssueCustomerId
                                                                           ==. c ^. CustomerId)
                                                              return (i, f, c)
      In the expression:
        do customer_issues_followUps_list <- runDB
                                               $ E.select $ E.from $ \ (i, f, c) -> do ...
           let issues
                 = map listToMaybe . group . sort . fst . unzip
                     $ customer_issues_followUps_list
           defaultLayout
             $ do setTitle "Your Licenses"
                  (do ...)
   |
41 |     E.select $
   |     ^^^^^^^^^^...

尝试2：

{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE TypeFamilies #-}

module Handler.Support where

import           Import hiding ((==.))
import qualified Database.Esqueleto as E
import           Database.Esqueleto      ((^.), (==.), (&&.))
import           Data.Traversable

getSupportR :: CustomerId -> Handler Html
getSupportR customerId = do
  customer_issues_followUps_list <- runDB $
    E.select $
    E.from $ \(i `E.InnerJoin` f `E.InnerJoin` c) -> do
    E.on (c ^. CustomerId ==. i ^. IssueCustomerId)
    E.on (i ^. IssueId ==. f ^. FollowUpIssueId)
    E.where_ (i ^. IssueCustomerId ==. E.val customerId)
    return (i, f, c)
  let issues = map listToMaybe . group . sort . fst . unzip $ customer_issues_followUps_list
  defaultLayout $ do
    setTitle "Your Licenses"
    $(widgetFile "support-display")

错误2：

/home/hhefesto/dev/laurus-nobilis/src/Handler/Support.hs:40:5: error:
    • Couldn't match type ‘(ra, rb, rc)’ with ‘(Entity Issue, b0)’
        arising from a functional dependency between:
          constraint ‘Database.Esqueleto.Internal.Sql.SqlSelect
                        (E.SqlExpr (Entity Issue), E.SqlExpr (Entity FollowUp),
                         E.SqlExpr (Entity Customer))
                        (Entity Issue, b0)’
            arising from a use of ‘E.select’
          instance ‘Database.Esqueleto.Internal.Sql.SqlSelect
                      (a2, b2, c) (ra2, rb2, rc2)’
            at <no location info>
    • In the second argument of ‘($)’, namely
        ‘E.select
           $ E.from
               $ \ (i `E.InnerJoin` f `E.InnerJoin` c)
                   -> do E.on (c ^. CustomerId ==. i ^. IssueCustomerId)
                         E.on (i ^. IssueId ==. f ^. FollowUpIssueId)
                         ....’
      In a stmt of a 'do' block:
        customer_issues_followUps_list <- runDB
                                            $ E.select
                                                $ E.from
                                                    $ \ (i `E.InnerJoin` f `E.InnerJoin` c)
                                                        -> do E.on
                                                                (c ^. CustomerId
                                                                   ==. i ^. IssueCustomerId)
                                                              E.on
                                                                (i ^. IssueId
                                                                   ==. f ^. FollowUpIssueId)
                                                              ....
      In the expression:
        do customer_issues_followUps_list <- runDB
                                               $ E.select
                                                   $ E.from
                                                       $ \ (i `E.InnerJoin` f `E.InnerJoin` c)
                                                           -> do ...
           let issues
                 = map listToMaybe . group . sort . fst . unzip
                     $ customer_issues_followUps_list
           defaultLayout
             $ do setTitle "Your Licenses"
                  (do ...)
   |
40 |     E.select $
   |     ^^^^^^^^^^...

这是我的持久模型：

Customer
    email Text
    password Text
    firstName Text
    lastName Text
    address1 Text
    address2 Text
    city Text
    state Text
    zipCode Text
    country Text
    phone Text
    organization Text
    UniqueCustomer email
    deriving Typeable
    deriving Show
    deriving Eq
    deriving Ord
License
    licenseAlias Text
    expirationDate UTCTime
    assignedTo CustomerId
    customerId CustomerId
    deriving Show
    deriving Eq
    deriving Ord
Issue
    customerId CustomerId
    issueSummary Text
    issueDetails Text
    issueState Int
    issueDate UTCTime
    deriving Show
    deriving Eq
    deriving Ord
FollowUp
    issueId IssueId
    followUpDate UTCTime
    followUpAuthor CustomerId
    followUpText Text
    deriving Show
    deriving Eq
    deriving Ord


-- Soon to be deleted:
Email
    email Text
    customerId CustomerId Maybe
    verkey Text Maybe
    UniqueEmail email
Comment json -- Adding "json" causes ToJSON and FromJSON instances to be derived.
    message Text
    customerId CustomerId Maybe
    deriving Eq
    deriving Show

如您所见，两次尝试中的错误是相同的：它期望使用元组而不是三元组。

任何帮助将不胜感激 ：）

Answer 1

罪魁祸首在let陈述中：

let issues = map listToMaybe . group . sort . fst . unzip $ customer_issues_followUps_list

fst和unzip与元组一起使用，因此编译器暗示customer_issues_followUps_list是元组。

为了解决这个问题，只需加上“-extra”你package.yml依赖（或者你的阴谋文件）并更换fst并unzip与fst3和unzip3在let像这样的语句：

let issues = map listToMaybe . group . sort . fst3 . unzip3 $ customer_issues_followUps_list