On Jul 18, 7:41 am, Torsten Bronger <[EMAIL PROTECTED]>
wrote:
> > Can I ask why you would need to change PKs?
>
> Yes. We are a scientific institution, and I create a samples
> database. Frequently a sample gets a new name, however, the old
> name(s) must be kept as aliases.
>
> For the aliases, I probably will use a second table with many-to-one
> relationship.
>
> I wanted to keep the (current) sample name the primary key because I
> think that this accelerates lookup, but if all else fails, I must
> use a surrogate key.
Clearly, a growing set of names is not a sufficiently unique and
immutable primary key for your data. I'd suggest something like a
composite key made of date/time, sample no., and fk to experiment
(whatever an experiment's pk is), but django doesn't support composite
keys. So a "surrogate" is a good compromise here. As for names, since
each sample can have multiple names, it should be a separate table
with a foreign key to the samples table.
class Experiment(models.Model):
date = ...
etc ....
class Sample(models.Model):
experiment = models.ForeignKey(Experiment)
date = models.DateTimeField()
sampleno = models.PositiveIntegerField()
... data ...
class Meta:
unique_together = (('experiment', 'date', 'sampleno'),)
class SampleName(models.Model):
sample = models.ForeignKey(Sample)
name = models.CharField(max_length = 60)
named = models.DateTimeField()
Primary keys never change over time.
-Jim
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