Modify column in django migration

0001_initial.py

# -*- coding: utf-8 -*-
# Generated by Django 1.11.6 on 2017-10-19 13:31
from __future__ import unicode_literals

from django.conf import settings
from django.db import connection, migrations, models
from django.db.migrations import RunPython

PROJECT_NAMESPACE = settings.PROJECT_NAMESPACE


def forward(apps, schema_editor):
    """Modify the `approve_token` to `utf8mb4_bin` collation."""
    NotifyEmail = apps.get_model(f'{PROJECT_NAMESPACE}_webshop', 'NotifyEmail')
    db_table = NotifyEmail._meta.db_table
    field_name = NotifyEmail._meta.get_field('approve_token').column
    field_size = NotifyEmail._meta.get_field('approve_token').max_length
    cursor = connection.cursor()
    cursor.execute(
        f'ALTER TABLE {db_table} MODIFY {field_name} '
        f'VARCHAR({field_size}) BINARY CHARACTER SET utf8mb4 COLLATE '
        'utf8mb4_bin NOT NULL')


class Migration(migrations.Migration):

    initial = True

    dependencies = [
    ]

    operations = [
        migrations.CreateModel(
            name='NotifyEmail',
            fields=[
                ('id', models.AutoField(
                    auto_created=True, primary_key=True, serialize=False,
                    verbose_name='ID')),
                ('first_name', models.CharField(
                    max_length=171, verbose_name='First name')),
                ('last_name', models.CharField(
                    max_length=171, verbose_name='Last name')),
                ('email', models.EmailField(
                    max_length=171, unique=True, verbose_name='Email')),
                ('is_activated', models.BooleanField(
                    default=False, verbose_name='Is activated')),
                ('approve_token', models.CharField(
                    max_length=50, unique=True, verbose_name='Approve token')),
                ('added_at', models.DateTimeField(
                    auto_now_add=True, verbose_name='Added at')),
            ],
            options={
                'verbose_name': 'Notify email',
                'verbose_name_plural': 'Notify emails',
            },
        ),
        RunPython(code=forward)
    ]