How to Override Django\'s Save Method for Selective Model Updating?

Django Override Save for Model Only in Some Cases

Problem:

When saving a Django model, you need to resize an image if a new image is added. However, you want to skip resizing if only the model's description is updated.

Solution:

To achieve this, you can create a custom property that acts as a setter for the image field and a flag to indicate whether the image has changed.

<code class="python">class Model(model.Model):
    _image = models.ImageField(upload_to='folder')
    thumb = models.ImageField(upload_to='folder')
    description = models.CharField()

    def set_image(self, val):
        self._image = val
        self._image_changed = True

    def get_image(self):
        return self._image

    image = property(get_image, set_image)

    def save(self, *args, **kwargs):
        if getattr(self, '_image_changed', True):
            small = rescale_image(self.image, width=100, height=100)
            self.image_small = SimpleUploadedFile(name, small_pic)
        super(Model, self).save(*args, **kwargs)</code>

This solution ensures that the image is resized only when it is changed, while avoiding resizing when only the description is updated. Additionally, this approach maintains compatibility with Django's pseudo-auto tools like ModelForm and contrib.admin.

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