Simple DB Access

Christian S <>
Sat Aug 5 00:20:20 CEST 2006


On 8/4/06, Ryan Rawson <> wrote:
> I dont think you have to make it harder to use adhoc concat SQL, just
> make it stupidly easy to use binds.  Screw the whole 'prepare
> statement' b.s. - that is why people dont use bind variables, you have
> to create tons of extra variables and tracking things just to use a
> bind.  Instead, push all that down into the API, and just provide an
> api like:
>
> execSql( string SQLText, bind1value, bind2value, bind3value )
>
> or something.  Hash the SQLText in the API so you can see if this was
> already prepared or not.

Since it is easy to use pattern matching to tell if SQLText is an atom one could
still allow registering statements, and only then take advantage of
statement preparation.
If it is a string, one just parse it over again. Erlang doesnt have
varargs, but we have
list litterals. Is it more fun to do:

edbc:execute(Db, "SELECT * FROM foobar WHERE a = ? AND b = ?", ["foo", "bar"])

than

edbc:execute(Db, "SELECT * FROM foobar WHERE a = ?a AND b = ?b", [{a,
"foo"}, {b, "bar"}])

The later has potential to report better error messages, telling you
that "parameter b still unbound" if no {b, Value} was given. Of
course, erlang has a tradition of giving vague error messages. :)

> Now, what is easier to write:
>
> execSql( "insert into foo (a,b,c)  values(" + escapeForSql( variable1
> ) + "," + .  <etc etc> )

Yeah, I get it. :) I think SQLite mainly had an
escape-this-string-for-inclusion-as-a-litteral-in-a-statement
approach. They do have it for blobs anyway. (Just me braindumping, I
investigated that api to get a sense of sql api/protocol diversity.)

<< Anyone have a SQL92 parser written in erlang/yecc alraedy? :)  Not?
Know where the bnf for SQL92 can be found? I recall seeing it in a
book appendix once.>>

Oh yeah. Postgres has a number of non-standard operators for quering
map databases. With a SQL92 parser front end one would reject sql
statements using them and force those users to "hit the metal" with
the postgres driver directly. Good/Bad?

> if it is a function that returns values, return a list of tuples
> (result set).  Remember that for like 90% of the database APIs unless
> you do "magic" the client side will retrieve the entire resultset from
> the server anyways.  Many times I've thought that I could retrieve one
> row at a time, then my client crashed because it tried to pull down
> 500,000 rows.  You need a special call series for those cases (which
> are generally special) - optimize the most common case, that would be
> returning a small to medium # of rows (eg: 1-500 rows).

Good that you bring this up, one ends up wondering how to handle huge
query results while making sql apis. How about the simple query
returns all as a result, leading to crashes if the result is big
enough to exhaust memory, and then a secondary version that can handle
some result-set like approach.

Is it better to use a lists:fold like approach than returning a result
set object for which one have various accessors and operators on? I
suspect the first leads to compact code which is easily readable for
erlang programmers with good grasp of first class functions, but quite
the opposite for newbies with an imperative-programming mindset.

> Also, for SQL that returns no rows (update, insert, etc), the # of
> rows affected is your resultset.  Don't provide 2 API calls that the
> programmer needs to figure out which one to call depending on select
> or update.

Returning different tuples for different statement results is
effectively two kinds of calls. But something like the following isnt
bad, is it?

case edbc:execute(...) of
  {result, Columns} ->
    ...;
  {update, Count) ->
    ...;
  . . .
end

Databases return different amount of information in their results.
Postgres is quite rich, afaik it returns column names and column types
(coded to numbers), beyond just the resulting rows. For every kind of
query it will also tell if you are outside a transaction, inside a
transaction, or inside an aborted transaction.

One needs to know what every db will present in results. I suspect
JDBC have done that job for us?

> That is my API design guide.  Having using our own internal API to OCI
> which behaves like I described more or less (except more like
> sprintf/scanf in terms of providing binds, ie: pointers) vs JDBC,
> Hibernate, PostgreSQL C api, i highly prefer our own API, despite the
> C warts it has.

I spent an hour clicking through the OCI docs a few days ago. Seems like plenty
information about the C OCI api there in.
They're not documenting the wire protocol, are they? How is your
in-house lib built, reverse engineering or some NDA deal with Oracle?
Have any experience with the OCI lib? Good enough to use as a
linked-in-driver? Reentrant to run in a separate thread?

> So for the love of all good API design, PLEASE don't make the
> developer do all the work!



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