[sqlalchemy] Re: Save the default function into the database
Thank you for the advices. I just come across an interesting database software kexi (www.kexi- project.org), there one can store the designs, queries and scripts into the database. And the database is in itself SQLite only, which does not support complicated database user-defined functions. So that basically all the information needed to retrieve all the function of the database is just in one file (as it is SQLite based), which is quite portable. Does anyone know how they achieved this? Rick Morrison wrote: I guess you know that storing the actual bytecodes (or the source) of a Python function in the database itself is not going to buy you much: Since the function bytecodes or source would be in Python, only a Python interpreter could run it to produce the function result, and if you know you're going to be accessing the database via a Python interpreter (most likely via SA), then you may as well just bundle the function in a module, import it and use it there like the rest of us do. If your'e searching for some more portable database logic that can be run from both a Python interpreter and other types of tools, you want database user-defined functions (UDF)s and stored procedures. SA supports several database that sport one or both of these tools: Oracle both SQL Server both Mysql both Postgresql functions only, but can modify data like stored procedures All of these will run the UDF or the stored procedure in the process of the database server, not in the context of your Python program. That means you won't be able to access variables in your Python program from the UDF or procedure, you'll need to supply them as parameters. If you really have to have the function be a Python function, the PLPython language for Postgresql allows you to run a real Python interpreter in the context of the server itself. There was a guy named James Pye who was working on a full-blown Python programming environment for Postgresql in which Python would be a full stored procedure language and could share variables with SQL and lots of other interesting stuff. Might be worth checking into -- check PGforge or Postgres contrib. Good luck with this, Rick --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: Save the default function into the database
Paul Johnston wrote: Hi, generate the default values (default = _some_python_function_). The problem is that such function is not saved in the database itsself. Ok, I wonder, why is this a problem for you? Usually people are happy with ORM-specific logic (such as this) just being stored in a python module and not the database. It is nice being able to default to some logic inside the database because if there's access to it using some other tool or even directly through SQL commands then the default would still be applied / applicable. One other possibility is to code the default inside a database trigger. But then you can't say that you have a NOT NULL column because if you omit the value then you'll get an SQL error... (While you can say, for example, INSERT INTO table (column) VALUES (DEFAULT) to get the default value.) --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: Save the default function into the database
On Nov 11, 2007, at 2:55 PM, Jorge Godoy wrote: One other possibility is to code the default inside a database trigger. But then you can't say that you have a NOT NULL column because if you omit the value then you'll get an SQL error... (While you can say, for example, INSERT INTO table (column) VALUES (DEFAULT) to get the default value.) im fairly certain triggers used to generate INSERT values are compatible with NOT NULL columns. although in this particular thread I dont think I understand the issue exactly, it seemed like it was just asking for some Python function to be executed external to the database value itself; in which case the solution is to use a custom TypeEngine or TypeDecorator class. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: Save the default function into the database
Michael Bayer wrote: im fairly certain triggers used to generate INSERT values are compatible with NOT NULL columns. although in this particular thread I dont think I understand the issue exactly, it seemed like it was just asking for some Python function to be executed external to the database value itself; in which case the solution is to use a custom TypeEngine or TypeDecorator class. I had the impression that it was about database functions, not Python functions. Maybe I thought that because I was working with stored procedures by the time :-) --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: Save the default function into the database
I guess you know that storing the actual bytecodes (or the source) of a Python function in the database itself is not going to buy you much: Since the function bytecodes or source would be in Python, only a Python interpreter could run it to produce the function result, and if you know you're going to be accessing the database via a Python interpreter (most likely via SA), then you may as well just bundle the function in a module, import it and use it there like the rest of us do. If your'e searching for some more portable database logic that can be run from both a Python interpreter and other types of tools, you want database user-defined functions (UDF)s and stored procedures. SA supports several database that sport one or both of these tools: Oracle both SQL Server both Mysql both Postgresql functions only, but can modify data like stored procedures All of these will run the UDF or the stored procedure in the process of the database server, not in the context of your Python program. That means you won't be able to access variables in your Python program from the UDF or procedure, you'll need to supply them as parameters. If you really have to have the function be a Python function, the PLPython language for Postgresql allows you to run a real Python interpreter in the context of the server itself. There was a guy named James Pye who was working on a full-blown Python programming environment for Postgresql in which Python would be a full stored procedure language and could share variables with SQL and lots of other interesting stuff. Might be worth checking into -- check PGforge or Postgres contrib. Good luck with this, Rick On 11/11/07, luyang.han [EMAIL PROTECTED] wrote: Hello all. The problem I want to solve is a little tricky. .I have created a table with some columns, which use other python functions to generate the default values (default = _some_python_function_). The problem is that such function is not saved in the database itsself. By just simple reading from the database one cannot get this function out. So the problem is how to save such construction into the database as well as how to retrieve these. I have some ideas but have not yet experimented. 1. One can save the corresponding function as a separate py file and refer to this file in some metadata for the table, and the program tries to get this py file. 2. Or one can pickle this default python function and save it to the metadata for the table. 3. Or one can simple pickle the Table or Column object and save it to somewhere in the database? Does anyone has similar experience? Any advices? --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
