[Ur] More questions

[Marc Weber]

Excerpts from Adam Chlipala's message of Mon Dec 13 00:16:13 +0100 2010:
> Marc Weber wrote:
> I don't see any obvious problem in the above that would lead to no rows 
> being inserted, but I don't know which code for [Enum.to] you have in 
> mind.  I'd guess there's a bug where it's returning an empty list.

The code can be found in the library playground (-> wiki).
You can see that I added {[show numbers]} and the page showed

  0 :: 1 :: 2  [...] :: 10 :: Nil

or such.

postgresql server says:

    LOG:  statement: BEGIN ISOLATION LEVEL SERIALIZABLE
    LOG:  execute uw2: DELETE FROM uw_Main_st AS T_T WHERE (1::int8 = 1::int8)
    LOG:  execute uw3: INSERT INTO uw_Main_st (uw_A, uw_B, uw_C, uw_Id) VALUES (E'TEXT A'::text, E'TEXT B'::text, $1::text, (- 20::int8))
    DETAIL:  parameters: $1 = '1 :: 2 :: 3 :: 4 :: 5 :: 6 :: 7 :: 8 :: 9 :: 10 :: []'
    LOG:  statement: COMMIT

for this code (pay attention to the last lonely INSERT which inserts the
list itself to proof that its not empty):

  table st : {Id : int, A : string, B: string, C: string}

  fun speed_test_insert () =
    let
      val numbers = Enum.to 1 10
    in
      dml (DELETE FROM st WHERE 1 = 1);
      list <- (List.mapM (fn i => dml (INSERT INTO st (Id, A, B, C) VALUES ({[i]}, {["TEXT A"]}, {["TEXT B"]}, {["TEXT C"]}) ) ) numbers);
      dml (INSERT INTO st (Id, A, B, C) VALUES (-20, {["TEXT A"]}, {["TEXT B"]}, {[show numbers]}) );
      return (page "refreshed" <xml>{[show numbers]}</xml>)
    end

So would you mind running the same test on your machine?

> BTW, you could write [TRUE] instead of [1 = 1].  IMO, it's slightly 
> nicer looking.

I'd say ur could support DELETE without dummy where. That would be even
prettier :)



> > 2)
> >    Tree demo:
> >        A witness that key belongs to the type class sql_injectable_prim,
> >        which indicates that both key and option key are fair game to use with SQL
> >
> >    What does this exactly mean?
> 
> [sql_injectable] is an abstract type family.  This means that its 
[...] I'll delay trying to understand all details. I tried asking: Why
is this line necessary. I would have no chance coming up with that line
myself. Shouldn't the information whether a key is nullable be encoded
in the type ?

The code looks like this:

    functor Make(M : sig
                     type key
                     [...]
                     val key_inj : sql_injectable_prim key

Marc Weber