Post empty date field error with Django rest framework

Question

model.py

class Form(models.Model):
    no = models.IntegerField()
    finish_date = models.DateField(blank=True, null=True)

serializers.py

class FormSerializer(serializers.ModelSerializer):
    class Meta:
        model = Form
        fields = '__all__'

if I try:

http http://127.0.0.1:8000/api/forms no=112 "finish_date"=""

It returns the error:

"finish_date": [
    "Date has wrong format. Use one of these formats instead: YYYY[-MM[-DD]]."
]

If I set "finish_date" to null , this post works. And StringField(blank=True, null=True) will not get the error.

How to solve?

Could you post the serializer you are using ?

rajkris
– rajkris

2017-10-22 06:57:27 +00:00
Commented Oct 22, 2017 at 6:57 — rajkris, Commented Oct 22, 2017 at 6:57

Adonis Gaitatzis · Accepted Answer · 2020-12-03 22:45:57Z

The problem is that the DateTimeField doesn't currently support the allow_blank keyword argument.

It does however support allow_null, so you have two options:

Clean Data Before Sending

Scrub "finish_date": "" -> "finish_date": null *before sending to your server

If you are using JavaScript to submit your form, you'll probably have do something like this:

if (data["finish_date"] == "") {
    data["finish_date"] = null;
}

Clean Data After Receiving

Scrub "finish_date": "" -> "finish_date": None in your serializer.

You can easily do this using the .to_internal_value() method on the ModelSerializer

class FormSerializer(serializers.ModelSerializer):
    class Meta:
        model = Form
        fields = '__all__'

    def to_internal_value(self, data):
        # check for "finish_date": "" and convert to None
        # This must be done before .validate()
        if data['finish_date'] == '':
            data['finish_date'] = None
        return super(FormSerializer, self).to_internal_value(data)

the .to_internal_value() method is mentioned a lot in the Django Rest Framework Fields API Reference

rajkris · Accepted Answer · 2017-10-22 09:22:05Z

5

Now in the above model, you have a DateField, and the DateField accepts certain formats similar to the ones shown in the error in your post.When you post with:

http http://127.0.0.1:8000/api/forms no=112 "finish_date"=""

You are actually passing an empty string("") to the serializer, which is not a valid format for the DateField. Instead try the Post without passing the "finish_date" arg, I think it will work then. Or maybe you could pass with some default date in the past instead of passing an empty string .

edited Oct 22, 2017 at 9:22

answered Oct 22, 2017 at 8:41

rajkris

1,79311 gold badge1111 silver badges1717 bronze badges

5 Comments

Shihabudheen K M Over a year ago

how can i handle the default blank string in serializer itself, before entering validate it got the error, where i can override the model level validation ???

Sandeep Balagopal Over a year ago

Any idea why Django is not accepting empty string when null=True, blank=True ? Most of the other fields accept empty when null=True and blank=True.

rajkris Over a year ago

@SandeepBalagopal, most of the fields(like char, text), accept empty since '' is actually a valid string. Now when we use the combination null=True, blank=True in models and supply no value, the db stores null for the field(except for char and text field, where '' is stored). Now empty string is not a valid date format. So when we do not specify key('finish_date') of the date_field when posting, the db stores it as null. For a little bit more clarification refer: stackoverflow.com/a/8609425/8482471

rajkris Over a year ago

@ShihabudheenKM, the query you have posted is actually a frequent one. Now the best way to approach the current situation is to pass a default value or not mentioning the date_field key or passing value as null, in the post request, which I think have been mentioned above. Now for your question, maybe we can try something like mentioned here: stackoverflow.com/a/46910040/8482471. But if you ask me I think it will be better to leave this method alone and maybe since this is an exceptional case, maybe just do this in the view itself. That way it will look cleaner. Just my thought.

Adonis Gaitatzis Over a year ago

The best thing is to scrub the data so that '' becomes null since the serializers.DateField doesn't yet support allow_blank. This can be done either before submitting or by the serializer in the .to_internal_value() method.

Draeko · Accepted Answer · 2022-01-25 02:52:51Z

1

Modify your serializer with this code

class FormSerializer(serializers.ModelSerializer):

finish_date = serializers.DateTimeField(allow_null=True)

class Meta:
    model = Form
    fields = '__all__'

answered Jan 25, 2022 at 2:52

Draeko

11122 silver badges1212 bronze badges

Comments

Akhil Kokani · Accepted Answer · 2023-02-28 04:16:39Z

As of ver. 3x DJango Rest Framework does not provide DateField which allows blank values, you either do not have to send the field in the payload or explicitly set null as the field value, but you cannot set "" blank values.

To solve this issue, I have implemented my own custom field which is built on top of DRF DateField, so you do not have to worry about compromising on your existing requirements! ;)

# sample.py

from rest_framework import serializers


class DateField(serializers.DateField):
    """
    Date field which allows blank values.

    As of djangorestframework 3x, DRF does not provide a date field which
    allows blank ("") values, so this field is built on top of DRF DateField
    which provides functionality to accept blank values.
    """

    allow_blank = None

    def __init__(self, *args, **kwargs):
        self.allow_blank = kwargs.pop("allow_blank", False)
        super().__init__(format, *args, **kwargs)

    def to_internal_value(self, data):
        # calc length if blank values are allowed,
        # this improves performance a bit 
        if self.allow_blank:
            if len(data) == 0:
                return data
        return super().to_internal_value(data)
    
    def to_representation(self, value):
        # DRF by default returns None if no value is set
        # so no custom implementation is required
        return super().to_representation(value)

Usage:

from sample import DateField

my_date_field = DateField(
    allow_blank=True,
)

スラッシュ · Accepted Answer · 2019-11-25 17:02:07Z

-1

If anyone is having a problem with this issue and using a javascript client to post data, try sending undefined as a blank date

answered Nov 25, 2019 at 17:02

スラッシュ

2944 bronze badges

1 Comment

mirek Over a year ago

Doesn't work for me. It will not fail, but instead of removing the earlier date the old date stays in database.

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