CODEWITHSUNDEEP
pythondjangomemoryhashbinary
Serge Rogatch
Serge Rogatch

Reputation: 15040

How to get bytes from a BinaryField in Django?

Consider we have a model with a BinaryField:

from django.db import models
import hashlib

class Target(models.Model):
    # ...
    image = models.BinaryField(max_length=(1<<24)-1)
    # ...
    def __str__(self):
        return hashlib.md5().update(self.image).hexdigest()

Does the above code compute correctly the MD5 digest of the image? Or is there some method or variable inside BinaryField to get the memory to pass to the update() method?

UPDATE: When I try:

>>> from pathlib import Path
>>> t = Target(image=Path('../../Experiments/LoginError2.jpg').read_bytes())
>>> t

I'm getting the following error:

AttributeError: 'NoneType' object has no attribute 'hexdigest'

So what am I doing wrong?

Upvotes: 0

Views: 2173

Answers (2)

Serge Rogatch
Serge Rogatch

Reputation: 15040

So here's the conclusion: BinaryField can be assigned bytes and can be read as bytes.

In the above code the hashing was done wrongly, and the correct way is:

hashlib.md5(self.image).hexdigest()

Upvotes: 0

xyres
xyres

Reputation: 21779

In regard to your update about the AttributeError, you're calling the hexdigest() method incorrectly.

The thing is, update() method returns None, and you're pretty much trying to call hexdigest() on None. Chaining method calls like this only works if the previous method returns an actual object instead of None.

You'll have to do this call in multiple steps:

def __str__(self):
    m = hashlib.md5()
    m.update(self.image)
    return m.hexdigest()

Upvotes: 1

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