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Editorial Team
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Asked: 2026-06-15T05:43:01+00:00

So I’m new to Django… First some background on how we do things now.

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So I’m new to Django…

First some background on how we do things now. We have a custom php system but I am constructing an improved inventory management system in django using only the admin interface. We store part numbers, and it is essential that we do not store duplicates. Part numbers can sometimes be entered with hypens, periods, spaces, etc. We need to be sure that duplicate parts are not added no matter what kind of formatting is entered. With our existing non-django system, we use a regex to strip anything from the string that is not a-zA-Z0-9. The actual entered part number is persisted, and the cleaned number is persisted to the db as well. Then when someone is adding a new part or even searching for a part, this cleaned version of the part number helps to avoid this ambiguity. We do the same for the manufacturer name.

My way of emulating this in django was to add the part_number_clean field along with the part_number field to the model. Then I overrode the save method to calculate the clean part number like so (manufacturer as well):

def save(self, *args, **kwargs):
    self.manufacturer_clean = re.sub(r'[^a-zA-Z0-9]', '', self.manufacturer).lower()
    self.part_number_clean = re.sub(r'[^a-zA-Z0-9]', '', self.part_number).lower()
    super(CatalogProduct, self).save(*args, **kwargs)

The problem is, I need to unique on a combination of part number and manufacturer:

class Meta:
    unique_together     = ('part_number_clean ', 'manufacturer_clean ')

When I try to save a duplicate record, I get a database integrity violation. So it seems like django is evaluating the unique fields before the save function is called (which makes sense). I just need to know how or which method I should override to calculate these fields BEFORE any validation.

Additionally, I am interested in adding a third field to the unique_together mix that may or may not be filled out. If it is not filled it will just have an empty default value. I hope this will not cause any issues.

It would also be great if when the user tabbed-out of the manufacturer and part number fields, and both were not empty, some js would see if that product exists already, and offer the user the option to click a button and be whisked away to that record, before they waste their time filling out the rest of the data only to find that it already exists. I’m guessing this lies way outside the realm of the admin interface without serious hacking. Is there any way to somehow integrate this with the admin interface? Its working great for me up till now…

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1 Answer

  1. Editorial Team

    I figured it out. I’m posting the answer for anyone else that is curious. This was actually very simple in the end to implement in the model. All one needs to do is implement (override?) the clean() method of the model. In the method, I calculate and set my special fields, then be sure to call self.validate_unique() after. Works like a charm! No need to raise any exceptions, the form will display the error on top perfectly. Doing this in the save method will not work, as the exception cannot be thrown by your code or django at that point. Here is the code:

    class CatalogProduct(models.Model):
    manufacturer        = models.CharField(max_length=100)
    manufacturer_clean  = models.CharField('Manufacturer',max_length=100,blank=True,editable=False)
    part_number         = models.CharField(max_length=100)
    part_number_clean   = models.CharField('Part number',max_length=100,blank=True,editable=False)

    def clean(self):
        # Calculate manufacturer_clean and part_number_clean
        self.manufacturer_clean = re.sub(r'[^a-zA-Z0-9]', '', self.manufacturer).lower()
        self.part_number_clean = re.sub(r'[^a-zA-Z0-9]', '', self.part_number).lower()
        self.validate_unique()
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