Numeric fields in serializers – Django REST Framework

In Django REST Framework the very concept of Serializing is to convert DB data to a datatype that can be used by javascript. Every serializer comes with some fields (entries) which are going to be processed. For example if you have a class with name Employee and its fields as Employee_id, Employee_name, is_admin, etc. Then, you would need AutoField, CharField and BooleanField for storing and manipulating data through Django. Similarly, serializer also works with same principle and has fields that are used to create a serializer.
This article revolves around Numeric Fields in Serializers in Django REST Framework. There are three major fields – IntegerField, FloatField and DecimalField.

IntegerField

IntegerField is basically a integer field that validates the input against Python’s int instance.It is same as IntegerField – Django Models

It has the following arguments –

  • max_value Validate that the number provided is no greater than this value.
  • min_value Validate that the number provided is no less than this value.

Syntax –

field_name = serializers.IntegerField(*args, **kwargs)

FloatField

FloatField is basically a float field that validates the input against Python’s float instance.It is same as FloatField – Django Models



It has the following arguments –

  • max_value Validate that the number provided is no greater than this value.
  • min_value Validate that the number provided is no less than this value.

Syntax –

field_name = serializers.FloatField(*args, **kwargs)

DecimalField

DecimalField is basically a decimal field that validates the input against Python’s decimal instance.It is same as DecimalField – Django Models

It has the following arguments –

  • max_digits The maximum number of digits allowed in the number. It must be either None or an integer greater than or equal to decimal_places.
  • decimal_places The number of decimal places to store with the number.
  • max_value Validate that the number provided is no greater than this value.
  • min_value Validate that the number provided is no less than this value.
  • localize Set to True to enable localization of input and output based on the current locale.

Syntax –

field_name = serializers.DecimalField(*args, **kwargs)

How to use Numeric Fields in Serializers ?

To explain the usage of Numeric Fields, let’s use the same project setup from – How to Create a basic API using Django Rest Framework ?.
Now that you have a file called serializers in your project, let’s create a serializer with IntegerField, FloatField and DecimalField as the fields.

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# import serializer from rest_framework
from rest_framework import serializers
  
class Geeks(object):
    def __init__(self, integer, float_number, decimal_number):
        self.integer = integer
        self.float_number = float_number
        self.decimal_number = decimal_number
  
# create a serializer
class GeeksSerializer(serializers.Serializer):
    # intialize fields
    integer = serializers.IntegerField()
    float_number = serializers.FloatField()
    decimal_number = serializers.DecimalField()

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Now let us create some objects and try serializing them and check if they are actually working, Run, –

Python manage.py shell

Now, run following python commands in the shell



# import everything from serializers
>>> from apis.serializers import *

# create a object of type Geeks
>>> obj = Geeks(123, 123.10, 123.123)

# serialize the object
>>> serializer = GeeksSerializer(obj)

# print serialized data
>>> serializer.data
{'integer': 123, 'float_number': 123.1, 'decimal_number': '123.1230'}

Here is the output of all these operations on terminal –

numeric-fields-in-serializers-Django-REST-Framework

Validation on Numeric Fields

Note that prime motto of these fields is to impart validations, such as IntegerField validates the data to Python’s int only. Let’s check if these validations are working or not –

# Create a dictionary and add invalid values
>>> data={}
>>> data['integer'] = 10
>>> data['float_number'] = "String"
>>> data['decimal_number'] = 123

# dictionary created
>>> data
{'integer': 10, 'float_number': 'String', 'decimal_number': 123}

# deserialize the data
>>> serializer = GeeksSerializer(data=data)

# check if data is valid
>>> serializer.is_valid()
False

# check the errors
>>> serializer.errors
{'float_number': [ErrorDetail(string='A valid number is required.', 
code='invalid')]}
}

Here is the output of these commands which clearly shows email and phone_number as invalid –

numeric-fields-in-serializres-Django-REST-Framework

Advanced concepts

Validations are part of Deserialization and not serialization. As explained earlier, serializing is process of converting already made data into another data type, so there is no requirement of these default validations out there. Deserialization requires validations as data needs to be saved to database or any more operation as specified. So if you serialize data using these fields that would work.

Core arguments in serializer fields

Argument Description
read_only Set this to True to ensure that the field is used when serializing a representation, but is not used when creating or updating an instance during deserialization
write_only Set this to True to ensure that the field may be used when updating or creating an instance, but is not included when serializing the representation.
required Setting this to False also allows the object attribute or dictionary key to be omitted from output when serializing the instance.
default If set, this gives the default value that will be used for the field if no input value is supplied.
allow_null Normally an error will be raised if None is passed to a serializer field. Set this keyword argument to True if None should be considered a valid value.
source The name of the attribute that will be used to populate the field.
validators A list of validator functions which should be applied to the incoming field input, and which either raise a validation error or simply return.
error_messages A dictionary of error codes to error messages.
label A short text string that may be used as the name of the field in HTML form fields or other descriptive elements.
help_text A text string that may be used as a description of the field in HTML form fields or other descriptive elements.
initial A value that should be used for pre-populating the value of HTML form fields.

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