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module Y2018.M06.D15.Exercise where
More dater today, but with a dater-fix, too!
The tab-separated file (tsv) in this directory is a report of all duplicates-
by-article_id in our article database. Your job is to find all the 'older'
ids (not article_id) of the articles and create a SQL DELETE statement to
purge the database of these pesky duplicates!
(play Mission: Improbably theme-song)
import Data.Map (Map)
import Data.Time (Day)
-- below import available via 1HaskellADay git repostiory
import Control.Scan.CSV (rend) -- hint: maybe use this function
exDir, tsvFile :: FilePath
exDir = "Y2018/M06/D15/"
tsvFile = "duplicates.tsv"
-- the daters are:
type ArticleId = String
type Idx = Integer
data Article =
Art { idx :: Idx, uuid :: ArticleId, title :: String,
published, updated :: Maybe Day }
deriving (Eq, Show)
readArticleDuplicates :: FilePath -> IO [Article]
readArticleDuplicates dups = undefined
Given the following ordering-precedence:
define the Ord instance of Article
instance Ord Article where
compare a b = undefined
-- now that you have the Ord instance, sort the articles in order by article_id
sortedArticles :: [Article] -> Map ArticleId [Article]
sortedArticles arts = undefined
-- and from that sorting, write the following SQL DELETE statement that deletes
-- duplicates of article_id that are 'older' that the most recent-one
deleteStmt :: [Idx] -> String
deleteStmt ids = "DELETE FROM article WHERE id IN (" ++ listOut ids ++ ")"
listOut :: Show a => [a] -> String
listOut lst = undefined