[PD] Question about SQL Placeholder Implementation

Hans-Christoph Steiner hans at eds.org
Wed Dec 26 22:24:41 CET 2007

My idea for using this would be to pair the [sql_query] directly to  
the [sqlite] object, then the rest of the time, the data would be in  
the form of Pd messages.  I think for most people, they'll want to  
work in Pd messages as much as possible, then at the last possible  
moment, the Pd messages should be converted into SQL queries.

Also, since Pd objects visually represent instances, I think that the  
[sqlite] server object should represent one database.  If there are  
numerous [sqlite] objects representing the same database, then I  
think things will get confusing to the Pd user and in the C code.  We  
tried this in hidio, and it turned out to be a pain.  I am not sure  
if this is what you are proposing, though, but that is my  
understanding of it.

I'll take a look at your design once its out there.


On Dec 26, 2007, at 10:28 AM, Mike McGonagle wrote:

> Hans,
> From looking at this (I didn't compile the external yet), but my  
> first thought about your patch is that it would be very cumbersome  
> to have the result sets coming out of the "server" object. They  
> should be coming out of the "query" object, as that is the object  
> that is handling that particular result set. I kind of envision  
> that once someone has finished with creating the SQL queries, that  
> they would then create the processing code to handle each query.  
> That is something that is specific to the query, and not the  
> "server" object. The way that you have this, we would still need to  
> create a separate "query" and "server" object for each query. That  
> would make swapping the "server" object in and out very difficult,  
> as it would require replacing ALL of the "server" objects for each  
> query.
> Just to let you know, I need to clean up some more stuff, but I  
> will post my latest version of the "server" and "query" objects  
> tomorrow. I have not done a whole lot of testing, but I am able to  
> insert SQL and make the queries, and get results out. It also  
> handles errors and most recent insert row id stuff...
> Mike
> On Dec 22, 2007 1:27 AM, Hans-Christoph Steiner <hans at eds.org> wrote:
> I just committed my first stabs at a sketch for the [sql_query]  
> object.  It doesn't do anything yet, but it does recognize ?  
> placeholders as object arguments and creates inlets.  Other than  
> that, the only thing it currently does is crash :).
> http://pure-data.cvs.sourceforge.net/pure-data/externals/hcs/ 
> sql_query-help.pd
> http://pure-data.cvs.sourceforge.net/pure-data/externals/hcs/ 
> sql_query.c
> .hc
> On Dec 21, 2007, at 1:36 PM, Mike McGonagle wrote:
>> On 12/21/07, Mathieu Bouchard <matju at artengine.ca> wrote:
>> On Tue, 18 Dec 2007, Mike McGonagle wrote:
>> > [query <srv_id> insert into mytable (id, name, token) values (? 
>> f,'?s','?s')]
>> > In this example, the first placeholder would expect a Float,  
>> with the next
>> > two expecting a Symbol (just think of this as a variation on the  
>> printf
>> > string substitutions).
>> It looks more like the types of [t] [pack] [unpack] [expr] etc.
>> Yes, they are PD types.
>> You don't really need to type your data. SQL is largely typeless:  
>> at least
>> at the level of what you can put in one table cell, anything is a  
>> string.
>> It becomes typed (but auto-cast) when put in the cell, but rebecomes
>> untyped when taken out of the cell.
>> Yes, I know that these things can be stored in a typeless manner,  
>> but the functions that bind the SQL statement with their  
>> placeholders can be of any type, as there are functions for the  
>> various datatypes.
>> http://www.sqlite.org/c3ref/bind_blob.html
>> This link shows all the different functions used to bind the data  
>> to the statement placeholders.
>> http://dev.mysql.com/doc/refman/5.0/en/c-api-prepared-statement- 
>> datatypes.html
>> And if you look at how MySQL does this, while they only provide a  
>> single bind function, it does have the datatypes for the data in a  
>> structure that gets passed into the bind function.
>> Also, from looking at libdbi, it appears that they don't even  
>> bother with placeholders at all.
>> This is not an issue of how the user sees these things, it is how  
>> the C code interfaces with the database.
>> So, just how do we do this in a consistent manner when all the  
>> different interfaces don't support these things, AND if they do,  
>> they do them differently.
>> > but considering that the databases need to know the specific  
>> data types
>> > for each placeholder,
>> heh? do they?
>> SQLite does. MySQL appears to as well. And yes, it is possible to  
>> just force everything to be a string/c-string and be done with it.  
>> SQLite actually stores everything as a string anyway, despite the  
>> defined types in the create statement.
>> Mike
>>   _ _ __ ___ _____ ________ _____________ _____________________ ...
>> | Mathieu Bouchard - tél:+1.514.383.3801, Montréal QC Canada
>> -- 
>> Peace may sound simple—one beautiful word— but it requires  
>> everything we have, every quality, every strength, every dream,  
>> every high ideal.
>> —Yehudi Menuhin (1916–1999), musician
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> Peace may sound simple—one beautiful word— but it requires  
> everything we have, every quality, every strength, every dream,  
> every high ideal.
> —Yehudi Menuhin (1916–1999), musician


I have the audacity to believe that peoples everywhere can have three  
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