Resolving ValidationError: [u"'' value has an invalid date format. It must be in YYYY-MM-DD format."] in Django 1.9.2?
Question: Earlier I created two fields & migrated everything. after that I tried to add
three fields `title`,`about`,`birthdate` into the model. I created a model
like this :

    
    
    from __future__ import unicode_literals
    from django.utils import timezone
    from django.db import models
    
    # Create your models here.
    
    class APP1Model(models.Model):
        name = models.CharField(max_length=120)
        percentage = models.CharField(max_length=120)
        title = models.CharField(max_length=100,default='Title')
        birth_date = models.DateTimeField(blank=True, null=True)
        about = models.TextField(max_length=100,null=True,default='About Yourself')
    
        def __unicode__(self):
            return self.name
    

But when I try to migrate in python shell, it is showing a validation error
like this:

    
    
    Operations to perform:
      Apply all migrations: admin, contenttypes, auth, app1, sessions
    Running migrations:
      Applying app1.0005_auto_20160217_1346...Traceback (most recent call last):
      File "manage.py", line 10, in <module>
        execute_from_command_line(sys.argv)
      File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 353, in execute_from_command_line
        utility.execute()
      File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 345, in execute
        self.fetch_command(subcommand).run_from_argv(self.argv)
      File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 348, in run_from_argv
        self.execute(*args, **cmd_options)
      File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 399, in execute
        output = self.handle(*args, **options)
      File "/usr/local/lib/python2.7/dist-packages/django/core/management/commands/migrate.py", line 200, in handle
        executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
      File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 92, in migrate
        self._migrate_all_forwards(plan, full_plan, fake=fake, fake_initial=fake_initial)
      File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 121, in _migrate_all_forwards
        state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
      File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 198, in apply_migration
        state = migration.apply(state, schema_editor)
      File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/migration.py", line 123, in apply
        operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
      File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/operations/fields.py", line 62, in database_forwards
        field,
      File "/usr/local/lib/python2.7/dist-packages/django/db/backends/sqlite3/schema.py", line 221, in add_field
        self._remake_table(model, create_fields=[field])
      File "/usr/local/lib/python2.7/dist-packages/django/db/backends/sqlite3/schema.py", line 103, in _remake_table
        self.effective_default(field)
      File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/schema.py", line 210, in effective_default
        default = field.get_db_prep_save(default, self.connection)
      File "/usr/local/lib/python2.7/dist-packages/django/db/models/fields/__init__.py", line 728, in get_db_prep_save
        prepared=False)
      File "/usr/local/lib/python2.7/dist-packages/django/db/models/fields/__init__.py", line 1301, in get_db_prep_value
        value = self.get_prep_value(value)
      File "/usr/local/lib/python2.7/dist-packages/django/db/models/fields/__init__.py", line 1296, in get_prep_value
        return self.to_python(value)
      File "/usr/local/lib/python2.7/dist-packages/django/db/models/fields/__init__.py", line 1273, in to_python
        params={'value': value},
    django.core.exceptions.ValidationError: [u"'' value has an invalid date format. It must be in YYYY-MM-DD format."]
    

How to rectify this? I tried all solution i read here but it doesn't work?

I am using Django: 1.9.2

My migration File

    
    
    from __future__ import unicode_literals
    
    from django.db import migrations, models
    

class Migration(migrations.Migration):

    
    
    dependencies = [
        ('app1', '0004_auto_20160217_0427'),
    ]
    
    operations = [
        migrations.AddField(
            model_name='app1model',
            name='about',
            field=models.TextField(default='About Yourself', max_length=100, null=True),
        ),
        migrations.AddField(
            model_name='app1model',
            name='birth_date',
            field=models.DateField(blank=True, default='', null=True),
        ),
        migrations.AddField(
            model_name='app1model',
            name='title',
            field=models.CharField(default='', max_length=100),
        ),
    ]
    


Answer: I went through the same problem some months back.I Just deleted the birthdate
field changes in all the migration Files inside migration folder. Then I
replaced the birthdate with this code:-

    
    
    birthdate = models.DateTimeField(blank=True, null=True)                            
    

Then after applying migration ,it works fine...

