Dynamic setting of field values in Django based on the values of other fields

Question

Dynamic setting of field values in Django based on the values of other fields

My goal is to automatically set a default value for a field in Django based on the selection of another field. In this case, the field that needs the default value is linked to a foreign key.

class Product(models.Model):
        description = models.CharField('Description', max_length=200)
        price = models.FloatField('Price')

class Sell(models.Model):
        product = models.ForeignKey(Product)
        price = models.FloatField('Price')

Each "Product" has a default price or suggested price stored in the database. When a user wants to add a new sell entry in the Admin pages and selects a specific product, I need to dynamically copy the suggested price from the corresponding Product entry to the Sell entry's price field. However, I can't depend on the standard save method as the user might make changes during the process.

Is there an elegant way within Django to achieve this functionality without explicitly resorting to JavaScript?

javascript django autocomplete django-forms django-admin

Answer 1

Answer №1

To handle this situation, you have options like implementing a pre-save hook or overriding the save() method of the Sell model.

from django.db import models

class Product(models.Model):
    description = models.CharField('Description', max_length=200)
    price = models.FloatField('Price')

class Sell(models.Model):
    product = models.ForeignKey(Product)
    price = models.FloatField('Price')

    # Approach 1:
    from django.db.models.signals import post_save
    def default_subject(sender, instance, using):
        instance.price = instance.product.price
    pre_save.connect(default_subject, sender=Sell)

    # Approach 2:
    def save(self, *args, **kwargs):
        self.price = self.product.price
        super(Sell, self).save(*args, **kwargs)

Answer 2

To handle this situation, you have options like implementing a pre-save hook or overriding the save() method of the Sell model.

from django.db import models

class Product(models.Model):
    description = models.CharField('Description', max_length=200)
    price = models.FloatField('Price')

class Sell(models.Model):
    product = models.ForeignKey(Product)
    price = models.FloatField('Price')

    # Approach 1:
    from django.db.models.signals import post_save
    def default_subject(sender, instance, using):
        instance.price = instance.product.price
    pre_save.connect(default_subject, sender=Sell)

    # Approach 2:
    def save(self, *args, **kwargs):
        self.price = self.product.price
        super(Sell, self).save(*args, **kwargs)

Answer 3

Answer №2

If you're wondering how to update form field values dynamically on the Admin webpage, it will require client-side scripting with JavaScript. While Django's Admin does offer some scripts for tasks like adding or removing Inlines, it doesn't provide functionality at a deeper level.

In the context of Django's Admin, jQuery can be accessed through window.django.jQuery (or simply django.jQuery). The form field IDs generated by Django Forms remain stable in the output code. By identifying the Product selector and the Sell.price input field in the form code, you can utilize jQuery to create an event handler such as .change() or .on('change', ...) to automatically update the price when the Product selection changes.

In terms of enhancing this functionality in Django Admin, there is a feature called ModelAdmin.prepopulated_fields. However, it's important to note that prepopulated_fields does not support DateTimeField, ForeignKey, or ManyToManyField fields.

Answer 4

If you're wondering how to update form field values dynamically on the Admin webpage, it will require client-side scripting with JavaScript. While Django's Admin does offer some scripts for tasks like adding or removing Inlines, it doesn't provide functionality at a deeper level.

In the context of Django's Admin, jQuery can be accessed through window.django.jQuery (or simply django.jQuery). The form field IDs generated by Django Forms remain stable in the output code. By identifying the Product selector and the Sell.price input field in the form code, you can utilize jQuery to create an event handler such as .change() or .on('change', ...) to automatically update the price when the Product selection changes.

In terms of enhancing this functionality in Django Admin, there is a feature called ModelAdmin.prepopulated_fields. However, it's important to note that prepopulated_fields does not support DateTimeField, ForeignKey, or ManyToManyField fields.

Dynamic setting of field values in Django based on the values of other fields

Answer №1

Answer №2

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