Re: PK and FK questions
On Apr 7, 2010, at 11:45 AM, ojayred wrote: > Hello All, > > I am new to Django and thinking about migrating to Django from our > existing web environment. I had a couple of questions that I would > like help in answering them. Your insight is greatly appreciated. > Thank you. > > 1) Considering, there is no support for Multiple Primary keys, how > would Django react if my tables have multiple primary keys and I tried > to update or delete a record? I am just curious. I don't know the answer, but assuming you already have tables built in your database, you can run "manage.py inspectdb" to see what ORM code Django would generate from such a table. If it generates something useful, then you are in business. In short, test. It shouldn't pose too much of a problem in a development environment. > > 2) I read somewhere that each table must have one primary key? Some of > our tables have no primary keys. Then you are doing it wrong in your database. Every table should have a primary key, regardless of how few rows it may have. Otherwise, your database has (theoretically, not usually true in practice) no means of determining one row from another. As others have mentioned, a Django model by default uses an autoincremented integer field as an artificial primary key, if you don't otherwise specify a PK in the model definition. > > 3) Is there a limit on the number of Foreign Keys in a table? I don't believe Django imposes such a limit. More likely, such a limit would be imposed by your database. > > 4) How often would I need to patch and/or upgrade Django? And is this > a difficult procedure? It depends. If your web application faces the public Internet, you will want to start with a current release of Django, and stay up to date with security and bugfix releases. If your web app is internal-only, I would still argue you should update for bugfixes and security releases, but you could likely get away with not updating, depending on the security policies of your company. You mention your test environment is OpenVMS. I don't know much about OpenVMS, except to say that when I used VAX/VMS in college many years ago, it was not Unix. As such, I don't know whether Python will work on your system. Assuming it does, then Django itself should run well enough. That also means that standard Python facilities for managing module installations should also work. You can thus use Distribute and Pip to keep your Django install up to date fairly easily. The harder question is whether you will need to modify your application to run with the updated version of Django. The Django core developers make a very strong effort to maintain backwards compatibility, and you can thus assume that updating from e.g. version 1.1.0 to 1.1.1 will be painless. But migrating from 1.1.x to 1.2 will only be *mostly* painless. Again, you can assume that everything will be backwards-compatible, but there may be the odd exception in the case of a bugfix. Much more likely, there will be new and improved functionality introduced that you will want to use, that will necessitate changes in your code. For instance, 1.2 will introduce the ability to connect to multiple databases. The means of specifying multiple db connections in the settings file has of course changed to accommodate the new features, though the old settings structure will continue to work as-is. Finally, as you work on your application, you may find yourself needing to modify the database table structures -- assuming you allow Django's ORM to manage your tables, which is a common case. In that situation, the changes to the underlying DDL can be automated using a Django-aware schema migration tool. South (http://south.aeracode.org/) is one such tool. ---Peter Herndon -- You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-us...@googlegroups.com. To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-users?hl=en.
Re: PK and FK questions
For responses to 1 and 3. Is there somewhere I can look? I guess I will have to test these capabilities along with unique_together to resolve the Multiple PK issue. For 2, I will have to add them as suggested. For 4. Sorry, I couldn't understand. Can you explain it again. :) I have a test environment on an OpenVMS 8.3. What is south? Thanks Marcos & Hinnack -- You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-us...@googlegroups.com. To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-users?hl=en.
RE: Re: PK and FK questions
Hi, >> 1) Considering, there is no support for Multiple Primary keys, how >> would Django react if my tables have multiple primary keys and I tried >> to update or delete a record? I am just curious. sorry, I do not know... >> 2) I read somewhere that each table must have one primary key? Some of >> our tables have no primary keys. django adds one to each model, if you do not do it called "id" >> 3) Is there a limit on the number of Foreign Keys in a table? I do not think there is a limit, but do not know >> 4) How often would I need to patch and/or upgrade Django? And is this >> a difficult procedure? depends on your OS - if you are on debian: apt-get update / upgrade if it is a minor update - they cept a lot of focus on backward capabilities you may consider using south, if you have a lot of db changes yourself for migrating the db and the data regards Hinnack -- You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-us...@googlegroups.com. To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-users?hl=en.
Re: PK and FK questions
Hi, I'm not too experienced with django myself so I will let someone else answer the rest of your questions. But for 2, wouldn't it be fairly simple to create primary keys for these tables? worst case scenario you just add a column that is a auto_incremented int and run a script to set it for existing rows. On Wed, Apr 7, 2010 at 10:45, ojayred wrote: > Hello All, > > I am new to Django and thinking about migrating to Django from our > existing web environment. I had a couple of questions that I would > like help in answering them. Your insight is greatly appreciated. > Thank you. > > 1) Considering, there is no support for Multiple Primary keys, how > would Django react if my tables have multiple primary keys and I tried > to update or delete a record? I am just curious. > > 2) I read somewhere that each table must have one primary key? Some of > our tables have no primary keys. > > 3) Is there a limit on the number of Foreign Keys in a table? > > 4) How often would I need to patch and/or upgrade Django? And is this > a difficult procedure? > > -- > You received this message because you are subscribed to the Google Groups > "Django users" group. > To post to this group, send email to django-us...@googlegroups.com. > To unsubscribe from this group, send email to > django-users+unsubscr...@googlegroups.com > . > For more options, visit this group at > http://groups.google.com/group/django-users?hl=en. > > -- You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-us...@googlegroups.com. To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-users?hl=en.
PK and FK questions
Hello All, I am new to Django and thinking about migrating to Django from our existing web environment. I had a couple of questions that I would like help in answering them. Your insight is greatly appreciated. Thank you. 1) Considering, there is no support for Multiple Primary keys, how would Django react if my tables have multiple primary keys and I tried to update or delete a record? I am just curious. 2) I read somewhere that each table must have one primary key? Some of our tables have no primary keys. 3) Is there a limit on the number of Foreign Keys in a table? 4) How often would I need to patch and/or upgrade Django? And is this a difficult procedure? -- You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-us...@googlegroups.com. To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-users?hl=en.
