database persistence with mysql, sqlite

[coldpizza]

Hi,

I want to run a database query and then display the first 10 records
on a web page. Then I want to be able to click the 'Next' link on the
page to show the next 10 records, and so on.

My question is how to implement paging, i.e. the 'Next/Prev' NN
records without reestablishing a database connection every time I
click Next/Prev? Is it at all possible with cgi/mod_python?

For example, in a NON-web environment, with sqlite3 and most other
modules, I can establish a database connection once, get a cursor
object on which I run a single 'SELECT * FROM TABLE' statement and
then use cursor.fetchman y(NN) as many times as there are still results
left from the initial query.

How do I do the same for the web? I am not using any high-level
framework. I am looking for a solution at the level of cgi or
mod_python (Python Server Pages under Apache). To call
cursor.fetchman y(NN) over and over I need to pass a handle to the
database connection but how do I keep a reference to the cursor object
across pages? I use mysql and sqlite3 as databases, and I am looking
for an approach that would work with both database types (one at a
time). So far I have successfully used the following modules for
database access: sqlite3, mysqld, and pyodbc.

So far, with mysql I use 'SELECT * FROM TABLE LIMIT L1, L2' where L1
and L2 define the range for the 'Next' and 'Previous' commands. I
have to run the query every time a click a 'Next/Prev' link. But I am
not sure that this is the best and most efficient way. I suppose using
CURSOR.FETCHMAN Y(NN) would probably be faster and nicer but how do I
pass an object reference across pages? Is it possible without any
higher-level libraries?

What would be the proper way to do it on a non-enterprise scale?

Would SqlAlchemy or SqlObject make things easier with regard to
database persistence?

[Lawrence D'Oliveiro]

In message <11************ **********@22g2 000hsm.googlegr oups.com>, coldpizza
wrote:

So far, with mysql I use 'SELECT * FROM TABLE LIMIT L1, L2' where L1
and L2 define the range for the 'Next' and 'Previous' commands. I
have to run the query every time a click a 'Next/Prev' link. But I am
not sure that this is the best and most efficient way.

Try it first, then see what happens. Remember, premature optimization is the
root of all (programming) evil.

[Gerardo Herzig]

coldpizza wrote:

>Hi,

I want to run a database query and then display the first 10 records
on a web page. Then I want to be able to click the 'Next' link on the
page to show the next 10 records, and so on.

My question is how to implement paging, i.e. the 'Next/Prev' NN
records without reestablishing a database connection every time I
click Next/Prev? Is it at all possible with cgi/mod_python?

For example, in a NON-web environment, with sqlite3 and most other
modules, I can establish a database connection once, get a cursor
object on which I run a single 'SELECT * FROM TABLE' statement and
then use cursor.fetchman y(NN) as many times as there are still results
left from the initial query.

How do I do the same for the web? I am not using any high-level
framework. I am looking for a solution at the level of cgi or
mod_python (Python Server Pages under Apache). To call
cursor.fetchma ny(NN) over and over I need to pass a handle to the
database connection but how do I keep a reference to the cursor object
across pages? I use mysql and sqlite3 as databases, and I am looking
for an approach that would work with both database types (one at a
time). So far I have successfully used the following modules for
database access: sqlite3, mysqld, and pyodbc.

Apache/cgi just dont work this way. When apache receives a new request
(a cgi being called), it starts a new thread, it execute him, and gives
the client some result. AND THEN KILL THE THREAD. Altough i never used
it, what i think you need is fast cgi (fcgi), wich takes care of
persistent connections to a web server.

Cheers.
Gerardo

[coldpizza]

On Sep 24, 7:23 am, Lawrence D'Oliveiro <l...@geek-
central.gen.new _zealandwrote:

In message <1190502677.970 811.181...@22g2 000hsm.googlegr oups.com>, coldpizza
wrote:

So far, with mysql I use 'SELECT * FROM TABLE LIMIT L1, L2' where L1
and L2 define the range for the 'Next' and 'Previous' commands. I
have to run the query every time a click a 'Next/Prev' link. But I am
not sure that this is the best and most efficient way.

Try it first, then see what happens. Remember, premature optimization is the
root of all (programming) evil.

It turned out that the method above ('SELECT * FROM TABLE LIMIT L1,
L2') works ok both with mysql and sqlite3, therefore I have decided to
stick with it until I find something better. With Sqlite3 you are
supposed to use LIMIT 10 OFFSET NN, but it also apparently supports
the mysql syntax (LIMIT NN, 10) for compatibility reasons.

[M.-A. Lemburg]

On 2007-09-23 01:11, coldpizza wrote:

Hi,

I want to run a database query and then display the first 10 records
on a web page. Then I want to be able to click the 'Next' link on the
page to show the next 10 records, and so on.

My question is how to implement paging, i.e. the 'Next/Prev' NN
records without reestablishing a database connection every time I
click Next/Prev? Is it at all possible with cgi/mod_python?

For example, in a NON-web environment, with sqlite3 and most other
modules, I can establish a database connection once, get a cursor
object on which I run a single 'SELECT * FROM TABLE' statement and
then use cursor.fetchman y(NN) as many times as there are still results
left from the initial query.

How do I do the same for the web? I am not using any high-level
framework. I am looking for a solution at the level of cgi or
mod_python (Python Server Pages under Apache). To call
cursor.fetchman y(NN) over and over I need to pass a handle to the
database connection but how do I keep a reference to the cursor object
across pages? I use mysql and sqlite3 as databases, and I am looking
for an approach that would work with both database types (one at a
time). So far I have successfully used the following modules for
database access: sqlite3, mysqld, and pyodbc.

So far, with mysql I use 'SELECT * FROM TABLE LIMIT L1, L2' where L1
and L2 define the range for the 'Next' and 'Previous' commands. I
have to run the query every time a click a 'Next/Prev' link. But I am
not sure that this is the best and most efficient way. I suppose using
CURSOR.FETCHMAN Y(NN) would probably be faster and nicer but how do I
pass an object reference across pages? Is it possible without any
higher-level libraries?

What would be the proper way to do it on a non-enterprise scale?

Depends on what "enterprise " scale means to you :-)

The easiest way to get excellent performance for such queries is
using a long running process, mod_scgi and have the browser
send a session cookie for you to use to identify the request.
You can then open the connection and keep it open while the user
browses the site.

If you want to save yourself from most of the details,
just use Zope or Plone + e.g. our mxODBC Zope DA for the
database connection (it works with all the databases
you mention on Windows, Linux and Mac OS X).

Even if you don't want to code things using Zope/Plone,
you should still consider it for taking care of all the
middleware logic and then write your application as
separate package which you hook into Zope/Plone using
"external methods" or "Python scripts" (in their Zope
sense).

Would SqlAlchemy or SqlObject make things easier with regard to
database persistence?

Not really: they don't provide the session mechanisms you
would need.

--
Marc-Andre Lemburg
eGenix.com

Professional Python Services directly from the Source (#1, Sep 25 2007)

>>Python/Zope Consulting and Support ... http://www.egenix.com/
mxODBC.Zope.D atabase.Adapter ... http://zope.egenix.com/
mxODBC, mxDateTime, mxTextTools ... http://python.egenix.com/

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