On Thursday 15 November 2012 17:12:09 Carsten Fuchs wrote: > using Django 1.3 (soon 1.4), we use models like these: > class Staff(models.Model): > name = models.CharField(max_length=80) > class Period(models.Model): > staff = models.ForeignKey(Staff) > begin = models.DateField() > end = models.DateField(editable=False) # see below > # The actual data that describes this period, > # e.g. department, salary, ... > department = models.CharField(max_length=60) > class Meta: > ordering = ['begin'] > > There are normally several Period instances for each staff member, and > the set of periods for one staff member form a chronological sequence: > > A period begins at the day given in 'begin'. > It ends at the day before the *next* period begins. > > Thus, in our original design, there was no field 'end' in the Period > model, because logically, it was not needed. (The last period is > "open-ended".) > > However, we found that many queries are very difficult to build without > the 'end' (such as "Find all staff members in department X on November > 1st"), and thus are planning to add it as shown above. > > 'end' should always be computed automatically as the day before the > begin of the next period, but I don't know where this is best > implemented in the admin interface: > > class PeriodInline(admin.TabularInline): > model = Period > class StaffAdmin(admin.ModelAdmin): > inlines = [ PeriodInline ] > > (Note that it is not enough to consider the Period that changed -- > rather, it is the 'end' in *another* period (the one "before" it) that > must be modified and saved, too.) > > What is the proper hook or where the best place to do this?
Why do you want to do this only in the admin interface? Its a generic thing: every time you save/change a period you should set the end-date of the previous one. So I would do this with a post-save hook (aka signal) directly in the models.py. Or maybe even subclass your models save- operation. Have fun, Arnold
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