> Django adds an ID field to all models by default. Some questions about > that. > How are the values calculated. If Django asks the DB to provide it > those values, can we be sure, for all supported backends, that > 1. The ids are auto incrementing, (and not just unique).
If you let Django automatically give you an ID field (which happens by default), it will ensure this. Likewise, if you name your ID field something else and use an AutoField[1] it will automatically increment. However, Django gives the flexibility to make anything you want a key as long as it's unique. > 2. They start from zero. and what happens if you pre-load data? or are attaching to a legacy DB? If Django creates the DB, it uses the DB's defaults (which becomes a matter of configuring your DB to behave the way you want). > 3. The difference between successive ids is 1. If you're working in a multi-master DB environment, you often need to have a stride other than 1. Thus, master #1 starts at 1 and has an ID stride of 4 (using IDs 1,5,9,...); master #2 starts at 2 with the same stride of 4 (using IDs 2,6,10,...); master #3 starts at 3; and there may be an optional server 4 (one space in the stride is occasionally left open for a hot-swap spare so it can be brought up in parallel before taking down another machine or more spaces in the stride may be left for future growth) Django does provide the initial-sql[2] that would allow you to nuke the contents of your DB and initialize your counters to zero with an increment of one if you want, but it would be a bad thing to do by default. By default, Django does the "right" thing. When creating the field, it uses the DB default (which is usually 0 with an increment of 1). It allows you to override this using initial SQL. It allows you to make the ID a non-numeric field. -tim [1] http://www.djangoproject.com/documentation/model-api/#autofield [2] http://www.djangoproject.com/documentation/model-api/#providing-initial-sql-data --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
