[Haskelldb-users] An idea for joined queries and records on HaskellDB

[Kei H. <ex8...@gm...>]

Hi, I have an idea to extend Relation types and Record types into tuple-ed ones.
I wrote experimentally implementation to achieve this.
https://github.com/khibino/haskelldb/tree/tuple_join


Query of single table case is like below.


type RelX = RecCons X0 (Expr p0) (RecCons X1 ... )
tableX :: Table RelX
...
type RecordX = RecCons X0 p0 (RecCons X1 ... )

single :: Query (Rel RelX)
single =  do 
  tx <- table tableX
  ...
  project $ copyAll tx

querySingle :: Database -> IO [Record RecordX]
querySingle =  (`query` single)

As usual, joined query case, we have been required to re-compose joined type other than defined Relation and Record types.


type RelY = RecCons Y0 (Expr q0) (RecCons Y1 ... )
tableY :: Table RelY
...
type RelJoined = RecCons X0 (Expr p0) ( ... (RecCons Y0 (Expr q0) ... ) ... )
type RecordJoined = RecCons X0 p0 ( ... (RecCons Y0 q0 ... ) ... )

joined' :: Query (Rel Joined)
joined' =  do
  tx <- table tableX
  ty <- table tableY
  ...
  project
    $ copy x0 tx
    # copy x1 tx
    ...
    # copy y0 ty
    # copy y0 ty
    ...

queryJoined' :: Database -> IO [Record RecordJoined]
queryJoined' =  (`query` joined')


On my implementation, we can simply use tuple type in joined query case.
Not required to re-compose joined Reltion and Record types.

type RecordY = RecCons Y0 q0 (RecCons Y1 ... )

joined :: Query (Rel (RelX, RelY))
joined =  do
  tx <- table tableX
  ty <- table tableY
  ...
  project
    $ (,) <$> copyAll tx
          <*> copyAll ty

queryJoined :: Database -> IO [Record (RecordX, RecordY)]
queryJoined =  (`query` joined)


-- 
-- Kei Hibino
-- ex8...@gm...
--