How to Convert Django Model Objects to Dictionaries with Complete Field Retention?

Converting Django Model Objects to Dictionaries with Complete Field Retention

When working with Django model objects, it is often necessary to convert them into dictionaries to facilitate data manipulation or serialization. However, it can be challenging to achieve this while preserving all fields, including foreign keys and values marked as 'not editable'.

Limitations of Existing Approaches

Several common methods for converting model objects to dictionaries fall short in various ways:

• instance.__dict__: Excludes many-to-many relationships and misnames foreign key IDs.
• model_to_dict: Omits uneditable fields.
• model_to_dict(..., fields=...): Exacerbates the limitations of the standard model_to_dict.
• query_set.values(): Similar output to instance.__dict__, but retains foreign key ID misnaming and omits many-to-many relationships.

Custom Solution

To address these limitations, a custom function can be implemented:

from itertools import chain

def to_dict(instance):
    opts = instance._meta
    data = {}
    for f in chain(opts.concrete_fields, opts.private_fields):
        data[f.name] = f.value_from_object(instance)
    for f in opts.many_to_many:
        data[f.name] = [i.id for i in f.value_from_object(instance)]
    return data

This function retrieves values for all fields, including those marked as 'not editable'. Foreign keys are converted to IDs, and many-to-many relationships are preserved.

Example Usage

instance = SomeModel(...)
result_dict = to_dict(instance)

Output:

{'auto_now_add': ...,
 'foreign_key': ...,
 'id': ...,
 'many_to_many': [...],
 'normal_value': ...,
 'readonly_value': ...}

Additional Enhancement: Enhanced Model Printing

For improved debugging and data visibility, a printable model class can be defined:

from django.db import models
from itertools import chain

class PrintableModel(models.Model):
    def __repr__(self):
        return str(self.to_dict())

    def to_dict(instance):
        # Same implementation as the custom to_dict function
        ...
    
    class Meta:
        abstract = True

Subclassing models from PrintableModel will provide them with a condensed representation similar to the result of the to_dict function when calling repr().

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