DecimalField – Django Models

DecimalField is a field which stores a fixed-precision decimal number, represented in Python by a Decimal instance. It validates the input using DecimalValidator.

Syntax

field_name = models.DecimalField(max_digits=None, decimal_places=None, **options)

DecimalField has the following required arguments –

• DecimalField.max_digits

  The maximum number of digits allowed in the number. Note that this number must be greater than or equal to decimal_places.

• DecimalField.decimal_places

  The number of decimal places to store with the number.

For example, to store numbers up to 999 with a resolution of 2 decimal places, you’d use:

models.DecimalField(..., max_digits=5, decimal_places=2)

And to store numbers up to approximately one billion with a resolution of 10 decimal places:

models.DecimalField(..., max_digits=19, decimal_places=10)

Django Model DecimalField Explanation

Illustration of DecimalField using an Example. Consider a project named geeksforgeeks having an app named geeks.

Refer to the following articles to check how to create a project and an app in Django.

• How to Create a Basic Project using MVT in Django?
• How to Create an App in Django ?

Enter the following code into models.py file of geeks app.

from django.db import models
from django.db.models import Model
# Create your models here.

class GeeksModel(Model):
    geeks_field = models.DecimalField(
                         max_digits = 5,
                         decimal_places = 2)

Add the geeks app to INSTALLED_APPS

# Application definition

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'geeks',
]

Now when we run makemigrations command from the terminal,

Python manage.py makemigrations

A new folder named migrations would be created in geeks directory with a file named 0001_initial.py

# Generated by Django 2.2.5 on 2019-09-25 06:00

from django.db import migrations, models

class Migration(migrations.Migration):

    initial = True

    dependencies = [
    ]

    operations = [
        migrations.CreateModel(
            name ='GeeksModel',
            fields =[
                ('id',
                  models.AutoField(
                  auto_created = True,
                  primary_key = True,
                  serialize = False,
                  verbose_name ='ID'
                )),
                ('geeks_field', models.DecimalField(
                                        max_digits = 5,
                                        decimal_places = 2
                )),
            ],
        ),
    ]

Now run,

Python manage.py migrate

Thus, an geeks_field DecimalField is created when you run migrations on the project. It is a field to store datetime.date python object.

How to use DecimalField ?

DecimalField is used for storing python datetime.date instance in the database. One can store any type of decimal number in the database. Let’s try storing a decimal number in the model created above.

# importing the model
# from geeks app
from geeks.models import GeeksModel

# importing datetime module
import decimal

# creating an instance of
# datetime.date
d = decimal.Decimal(9.53)

# creating an instance of
# GeeksModel
geek_object = GeeksModel.objects.create(geeks_field = d)
geek_object.save()

Now let’s check it in admin server. We have created an instance of GeeksModel.

Field Options

Field Options are the arguments given to each field for applying some constraint or imparting a particular characteristic to a particular Field. For example, adding an argument null = True to DecimalField will enable it to store empty values for that table in relational database.
Here are the field options and attributes that a DecimalField can use.

Field Options	Description
Null	If True, Django will store empty values as NULL in the database. Default is False.
Blank	If True, the field is allowed to be blank. Default is False.
db_column	The name of the database column to use for this field. If this isn’t given, Django will use the field’s name.
Default	The default value for the field. This can be a value or a callable object. If callable it will be called every time a new object is created.
help_text	Extra “help” text to be displayed with the form widget. It’s useful for documentation even if your field isn’t used on a form.
primary_key	If True, this field is the primary key for the model.
editable	If False, the field will not be displayed in the admin or any other ModelForm. They are also skipped during model validation. Default is True.
error_messages	The error_messages argument lets you override the default messages that the field will raise. Pass in a dictionary with keys matching the error messages you want to override.
help_text	Extra “help” text to be displayed with the form widget. It’s useful for documentation even if your field isn’t used on a form.
verbose_name	A human-readable name for the field. If the verbose name isn’t given, Django will automatically create it using the field’s attribute name, converting underscores to spaces.
validators	A list of validators to run for this field. See the validators documentation for more information.
Unique	If True, this field must be unique throughout the table.