[DB-SIG] PROPOSAL: Portable Argment Format
Wed, 24 Jun 1998 10:33:08 -0400
M.-A. Lemburg wrote:
> Jim Fulton wrote:
> > I'd like to lobby for a portable argument format for the DBI
> > interface. While this *does* require parsing SQL, this is
> > not really all that hard and I think the benefits are well
> > worth the effort. I volunteer to provide a utility to assist
> > with this.
> Actually, it only requires scanning SQL. Parsing SQL would
> be overkill ;)
> > Here's what I think the format needs to do:
> > - Not interfere with SQL. That is, it must be unabiguous
> > to find parameters in SQL.
> > - Support optional argument names, which may be given
> > a positional interpretation.
> > - Capture type information, to make type explicit.
> There's a problem with this one: the database may want to
> have different types than the one you explicitly state in the
> SQL statement, e.g. when porting from e.g. Solid to MySQL
> you'll find that MySQL will want all parameters to be strings,
> even numbers, so statements like
> INSERT INTO MyTable VALUE (:t, :s, :i)
> would fail on MySQL.
No, because the MySQL interface would convert values to strings
as part of the conversion process.
> But then: the interface could implement
> the type checks and do the conversions afterwards...
> > Maybe this is all that's needed.
> > I propose the following format:
> > :(name)code
> > where : signals a parameter and code is a type code.
> > Valid type codes are:
> > c, b, B, h, H, i, I, l, L, f, d, and s --
> > as defined in the struct module
> > t -- Date/Time
> We ought to define three chars for date/time values:
> D - date only
> T - daytime only
> S - timestamp (date + daytime)
> since this is what many DBs can handle.
> > $ -- Money (???)
> Hmm, what would that look like ?
No idea. That's why I added question marks. OK, Punt.
> > r -- Binary data (raw/blob) gotten from a string
> > others...???
> · What will databases without some of these types get ? E.g. the money
> type is not defined in ODBC.
Perform some reasonable conversion.
> · Which Python types are expected for each type character ? E.g. will
> passing strings to ':r' be ok ?
:r is defined to come from a string above. The proposal should
spell this out.
> Will more than one type be allowed per
> type char (with automatic conversion if necessary) ?
Yes. This should be spelled out.
> > [Examples]
> Note that you can provide the whole functionality by coding
> a Python function (or class) on top of cursor.execute, so no change to
> the API spec is necessary. Moreover, every existing implementation
> will be able to use it without modification (which is a Good Thing :).
How? Each implementation has to be involved in implementing this.
For example, portable aguments have to be converted to platform-
specific arguments, and platform specific conversions have to be
applied. Utilities can be provided to make the implementation simpler,
but implementation-specific code is needed.
> You could even have a perpare constructor that returns a (Python)
> instance with a function call interface. [We don't have a
> performance issues here, since the function call overhead
> is negligable w/r to the time it takes for the database to finish.]
Right. With type information in the sql statement, I can do much
of the binding work up front and make the actual callinr process
simpler and faster.
Jim Fulton mailto:email@example.com
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