[FIXED] Django 5.0: How GeneratedField actually works?

Issue

I've read the Django documentation about the new models.GeneratedField, but I don't quite understand how it works inside a database.

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Can someone explain this?

Solution

The GeneratedField in Django 5.0 is a full-fledged field type designed for automatic calculation by the database whenever other fields in the same row are modified. This feature is invaluable for ensuring immediately available values calculated from other fields of the same model, provided they are in the same database table.

Key Attributes of GeneratedField:

expression: Defines the logic for automatic value setting by the database when the model changes. output_field: Specifies the data type of the generated field. db_persist: Indicates whether the field should be stored in the database.

Examples of GeneratedField Usage:

• Rectangle Model: A model with base and height fields can have an area GeneratedField, calculated by multiplying base and height.

from django.db import models
from django.db.models import F


class Rectangle(models.Model):
    base = models.FloatField()
    height = models.FloatField()
    area = models.GeneratedField(
        expression=F("base") * F("height"),
        output_field=models.FloatField(),
        db_persist=True,
    )

• Item Model: Demonstrates using the Round function to calculate total_price GeneratedField from price and quantity fields.

• Order Model: Showcases conditional expression in the status GeneratedField, using SQL CASE expression based on the payment field's null status.

• Event Model: Includes GeneratedFields like start_date, end_date (truncating dates), and duration (calculating time difference).

• Package Model: Uses JSON expressions to extract the version GeneratedField from a JSON data field.

In essence, GeneratedField in Django offers a robust way to manage database-calculated fields, enhancing database efficiency and reducing the need for additional data processing outside the database.

Answered By - saurav.codes