On Mon, 2007-11-12 at 13:38 -0600, Mike McGonagle wrote:
God, why do I do this?
I often ask myself that question!
- I think having the SQL query provided as an object creation argument
is a really bad idea. Wouldn't it be better to just pass the query in as a list
It seems mean to leave all formatting to the user, but that's most flexible in practice.
At the same time, the process of building the message to create the SQL that then gets submitted could be cumbersome. If it is just a simple thing like loading up a textfile, and then forwarding this on that is one thing (assuming that each line in the textfile is a complete SQL statement), but to construct dynamic SQL on the fly, that is a whole different thing.
I don't really understand what you mean. AFAICT we're just talking about the difference between passing the query to the object via its arguments, or passing the query as a message to the first inlet. The latter just seems easier because you already have variable substitution 'for free' in Pd's message passing, and you don't need to reinstantiate the object to change the query.
What's so crazy about constructing dynamic SQL? Already with [psql] (or [sqlsingle]) It's straightforward to do something like:
[metro 500] | [random 100] | [moses 60] | | | |sql SELECT * FROM chords WHERE dynamic=$1 sqlend( | / |sql INSERT INTO notes VALUES (2) sqlend( | / | / | / | / [psql mydb]
Or whatever...
And this doesn't even address the different types of SQL statements, each returning a different result set, or error code.
With [psql] the result of each query is returned as a set of 'tagged' tuples. In Pd terms this means each row in the result set comprises a discrete message prefixed with the row 'id', and with each column corresponding to a single atom. This means that you can distinguish the results of a single query from the results of multiple queries. Because the object uses a single connection to the database, and no threads, results are received in the order that queries are sent.
I have found this to work well, and I think it would also work well for sqlite4pd.
And then there is still the issue of having to parse through the result sets as they comeback...
list would basically be UNFORMATTED data, and it would require the PD code to interpret the result sets.
KISS. Object should know as little about databases as it can, it's all down to the object user and the service behind the object, object == gateway, nothing much more.
Ok, can anyone create a PD patch that might illustrate some of the ways you envision sending SQL to the database? Nothing "workable", just a prototype of what you see...
I'm sure you've already looked at it, but there's a (maybe) useful README and help file here:
http://pure-data.cvs.sourceforge.net/pure-data/externals/postlude/psql/
While I would tend to agree in keeping it simple. There are a couple of hurdles that must be crossed. On the one hand, I get the impression that some are thinking that it is as simple as saying "select * from my-table;" and then you are done, each SQL statement is potentially VASTLY different from the next, and to expect to create a single INSTANCE of a connection, and pipe all your requests through that one object, I think is a little naive.
What's naive about that? Isn't that how most database clients work: connect to the server, send queries through the connection. I think what you are doing with your approach is something like having one connection per query 'class' (type), but I don't think this approach is very common.
On the other hand, I would think that expecting a single object to handle this would result in a 'route'ing nightmare in the PD code in interpreting the result sets. While dealing with a single instance of an SQL statement that has known results, would be very manageable and not require a lot of routing.
That's true. Your solution could require less routing/unpacking on the results, but OTOH, it could make more if what the user wants is actually a list that they can route/unpack in pd. I also think you are making more work for yourself reinventing route, unpack etc inside your extern.
Jamie