Remove connLimitOffset #1325
Description
connLimitOffset is used in esqueleto, which has me investigating it.
These are the uses of the term in persistent repository:
λ ~/Projects/persistent/ master rg connLimitOffset
persistent-sqlite/Database/Persist/Sqlite.hs
291: , connLimitOffset = decorateSQLWithLimitOffset "LIMIT -1"
482: , connLimitOffset = decorateSQLWithLimitOffset "LIMIT -1"
persistent/ChangeLog.md
95: * The `connLimitOffset` function used to have a `Bool` parameter. This
persistent-postgresql/Database/Persist/Postgresql.hs
407: , connLimitOffset = decorateSQLWithLimitOffset "LIMIT ALL"
1778: , connLimitOffset = undefined
persistent/Database/Persist/SqlBackend.hs
119: func <- asks (SqlBackend.connLimitOffset . projectBackend)
persistent/Database/Persist/SqlBackend/Internal.hs
112: , connLimitOffset :: (Int,Int) -> Text -> Text
persistent/Database/Persist/Sql/Orphan/PersistQuery.hs
119: sql conn = connLimitOffset conn (limit,offset) $ mconcat
140: sql conn = connLimitOffset conn (limit,offset) $ mconcat
persistent/Database/Persist/SqlBackend/Internal/MkSqlBackend.hs
71: , connLimitOffset :: (Int,Int) -> Text -> Text
persistent-mysql/Database/Persist/MySQL.hs
155: , connLimitOffset = decorateSQLWithLimitOffset "LIMIT 18446744073709551615"
1303: , connLimitOffset = undefined
In other words, it is always assigned with the result of decorateSqlWithLimitOffset applied to that Text parameter.
λ ~/Projects/persistent/ master rg decorateSQLWithLimitOffset
persistent-sqlite/Database/Persist/Sqlite.hs
291: , connLimitOffset = decorateSQLWithLimitOffset "LIMIT -1"
482: , connLimitOffset = decorateSQLWithLimitOffset "LIMIT -1"
persistent-postgresql/Database/Persist/Postgresql.hs
407: , connLimitOffset = decorateSQLWithLimitOffset "LIMIT ALL"
persistent/Database/Persist/Sql.hs
57: , decorateSQLWithLimitOffset
persistent/Database/Persist/Sql/Orphan/PersistQuery.hs
14: , decorateSQLWithLimitOffset
485:decorateSQLWithLimitOffset
490:decorateSQLWithLimitOffset nolimit (limit,offset) sql =
persistent-mysql/Database/Persist/MySQL.hs
155: , connLimitOffset = decorateSQLWithLimitOffset "LIMIT 18446744073709551615"
That is implemented in Database.Persist.Sql.Orphan.PersistQuery here:
-- | Generates sql for limit and offset for postgres, sqlite and mysql.
decorateSQLWithLimitOffset
:: Text
-> (Int,Int)
-> Text
-> Text
decorateSQLWithLimitOffset nolimit (limit,offset) sql =
let
lim = case (limit, offset) of
(0, 0) -> ""
(0, _) -> T.cons ' ' nolimit
(_, _) -> " LIMIT " <> T.pack (show limit)
off = if offset == 0
then ""
else " OFFSET " <> T.pack (show offset)
in mconcat
[ sql
, lim
, off
]noLimit is necessary because MySQL and Sqlite throw a syntax error if you have an OFFSET without a corresponding LIMIT clause.
Since the noLimit parameter is actually what varies, let's store that in the record instead of the function. Then, decorating with LIMIT/OFFSET can be done as a function implemented directly.
This simplifies esqueleto's use-case.