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{-# LANGUAGE OverloadedStrings, QuasiQuotes, TupleSections #-}
module Y2017.M11.D28.Solution where
Just as yesterday where we added a set of recommended articles, today we are
going to delete a set of articles.
import Control.Monad
import qualified Data.ByteString.Char8 as B
import Database.PostgreSQL.Simple
import Database.PostgreSQL.Simple.SqlQQ
import Database.PostgreSQL.Simple.Types
-- below imports available via 1HaskellADay git repository
import Store.SQL.Connection
import Store.SQL.Util.Indexed
import Y2017.M11.D06.Solution
Actually, we want to build the query dynamically, otherwise we're executing
multiple delete statements, thus:
deleteRecsStmt :: Query
deleteRecsStmt =
[sql|DELETE FROM recommendation
WHERE for_article_id=? AND recommended_article_id=?|]
deleteRec :: Connection -> Integer -> [Integer] -> IO ()
deleteRec conn srcId recIds =
mapM_ (execute conn deleteRecsStmt)
(sequence (srcId, recIds))
we don't want this. So let's build a delete statement with the source article
id embedded into the the query then delete the recommended articles en masse.
deleteRec :: Connection -> Integer -> [Integer] -> IO ()
deleteRec conn srcId =
let query = "DELETE FROM recommendation WHERE for_article_id=" ++ show srcId
++ " AND recommended_article_id IN ?" in
void . execute conn (Query (B.pack query)) . Only . In
{-- BONUS -----------------------------------------------------------------
Write a program that takes a list of recommended article ids to delete and
deletes them.
main' :: [String] -> IO ()
main' artIds@(h:t1:t2) =
withConnection (\conn -> deleteRec conn (read h) (map read (t1:t2)))
main' _ = putStrLn (unlines ["","remover <srcId> <artId1> [artId2 ...]","",
"\tRemoves <artIds> associated to <srcId> from the recommendation table.",
{-- BONUS-BONUS -----------------------------------------------------------
This may not be your cup of tea, but here it is: write a PHP script that calls
this program with the _REQUEST arguments, then have that PHP script call
start on the source article id to return JSON of all the entries of the
recommendation table for that source article.
The PHP script is located at Y2017/M11/D28/remove_show.php
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