Question

So I have the following model structure for a django project

class RawData(models.Model):
    user = models.ForeignKey(User)
    timestamp = models.DateTimeField()
    ...
    value = models.PositiveIntegerField()

class SummarizedData(models.Model):
    SUMMARY_DURATION = (
        ('H', 'Hour'),
        ('D', 'Day'),
        ('M', 'Month'),
        ('Y', 'Year')
    )
    user = models.ForeignKey(User)
    duration = models.CharField(max_length=1, choices=SUMMARY_DURATION)
    timestamp = models.DateTimeField()      #for keeping track of which duration's data is this
    ...
    min_max_values = models.ManyToManyField(RawData)

Now my problem is related to min_max_values. I just want 2 RawData tuples per SummarizedData – one corresponding to the minimum RawData value seen for that duration, and the other for the maximum such value.

However since a particular RawData tuple could be the minimum value for more than one SummarizedData entries (for ex for a given hr, the same day etc), I related them through manytomany relation. But I am not able to figure out how to identify which of the 2 RawData values related to a SummarizedData is the max and which is the min unless I compare their respective values. So as of now I’m going with having functions in SummarizedData like getMaxValue and getMinValue.

My question is that for such a specific case, isn’t it possible to somehow include 2 fields in SummarizedData which each correspond to a single RawData field? Maybe like this?

min_value = models.OneToOneField(RawData)
max_value = models.OneToOneField(RawData)

Or should I just go with my first approach?

Edited

Sorry I should have used ForeignKey instead of OneToOneField

min_value = models.ForeignKey(RawData)
max_value = models.ForeignKey(RawData)

Answer 1

I don’t think you should store the data as a ManyToMany field because of the following reasons:

1. You will have to write explicit functions to determine which of the values is minimum and which is maximum
2. Any aggregation operation (like average, sum, min, max) or sorting etc (if shown in tabular format) would be easier if you store minimum or maximum values separately.

It will save a lot of extra calculations and you will need fewer lines of code to do whats required, so I would suggest you use separate ForeignKey fields for min_value and max_value

min_value = models.ForeignKey(RawData)
max_value = models.ForeignKey(RawData)