Set PeriodicTask.name max_length = 191 to avoid issues with MySQL indexes.

Add readme

Add test settings

Author: dilin-sp

README.rst

@@ -229,6 +229,17 @@ pip command::
 
     $ pip install https://github.com/celery/django-celery-beat/zipball/master#egg=django-celery-beat
 
+Issues with mysql
+-----------------
+ If you want to run ``django-celery-beat`` with MySQL, you might run into some issues.
+
+ One such issue is when you try to run ``python manage.py migrate django_celery_beat``, you might get the following error::
+     django.db.utils.OperationalError: (1071, 'Specified key was too long; max key length is 767 bytes')
+ To get around this issue, you can set::
+     DJANGO_CELERY_BEAT_NAME_MAX_LENGTH=191
+ (or any other value if any other db other than MySQL is causing similar issues.)
+ max_length of **191** seems to work for MySQL.
+
 .. |build-status| image:: https://secure.travis-ci.org/celery/django-celery-beat.svg?branch=master
     :alt: Build status
     :target: https://travis-ci.org/celery/django-celery-beat

django_celery_beat/migrations/0001_initial.py

@@ -4,6 +4,7 @@
 
 from django.db import migrations, models
 import django.db.models.deletion
+from django.conf import settings
 
 
 class Migration(migrations.Migration):
@@ -71,8 +72,15 @@ class Migration(migrations.Migration):
                     auto_created=True, primary_key=True,
                     serialize=False, verbose_name='ID')),
                 ('name', models.CharField(
-                    help_text='Useful description', max_length=200,
-                    unique=True, verbose_name='name')),
+                    help_text='Useful description',
+                    max_length=getattr(
+                        settings,
+                        'DJANGO_CELERY_BEAT_NAME_MAX_LENGTH',
+                        200
+                    ),
+                    unique=True,
+                    verbose_name='name'
+                )),
                 ('task', models.CharField(
                     max_length=200, verbose_name='task name')),
                 ('args', models.TextField(

django_celery_beat/migrations/0002_auto_20161118_0346.py

@@ -4,6 +4,7 @@
 
 from django.db import migrations, models
 import django.db.models.deletion
+import django_celery_beat.models
 
 
 class Migration(migrations.Migration):
@@ -50,3 +51,14 @@ class Migration(migrations.Migration):
                 to='django_celery_beat.SolarSchedule', verbose_name='solar'),
         ),
     ]
+    custom_operations = [
+        migrations.AddIndex(
+            model_name='periodictask',
+            index=django_celery_beat.models.CeleryMySQLIndex(
+                fields=['name'],
+                name='django_cele_name_9c39ec_idx'
+            )
+        )
+    ]
+
+    operations = operations + custom_operations

django_celery_beat/models.py

@@ -6,10 +6,12 @@
 import timezone_field
 from celery import schedules
 from celery.five import python_2_unicode_compatible
+from django.conf import settings
 from django.core.exceptions import MultipleObjectsReturned, ValidationError
 from django.core.validators import MaxValueValidator
 from django.db import models
 from django.db.models import signals
+from django.db.models.indexes import Index
 from django.utils.translation import ugettext_lazy as _
 
 from . import managers, validators
@@ -39,6 +41,23 @@ def cronexp(field):
     return field and str(field).replace(' ', '') or '*'
 
 
+class CeleryMySQLIndex(Index):
+    def create_sql(self, model, schema_editor, using=''):
+        sql_create_index = 'CREATE INDEX %(name)s ON %(table)s (%(columns)s(%(size)d))%(extra)s'
+        sql_parameters = self.get_sql_create_template_values(
+            model,
+            schema_editor,
+            using
+        )
+        sql_parameters['size'] = getattr(
+            settings,
+            'DJANGO_CELERY_BEAT_NAME_MAX_LENGTH',
+            200
+        )
+        sql = sql_create_index % sql_parameters
+        return sql
+
+
 @python_2_unicode_compatible
 class SolarSchedule(models.Model):
     """Schedule following astronomical patterns."""
@@ -248,8 +267,14 @@ class PeriodicTask(models.Model):
     """Model representing a periodic task."""
 
     name = models.CharField(
-        _('name'), max_length=200, unique=True,
-        help_text=_('Useful description'),
+        _('name'),
+        max_length=getattr(
+            settings,
+            'DJANGO_CELERY_BEAT_NAME_MAX_LENGTH',
+            200
+        ),
+        unique=True,
+        help_text=_('Useful description')
     )
     task = models.CharField(_('task name'), max_length=200)
     interval = models.ForeignKey(
@@ -316,6 +341,7 @@ class Meta:
 
         verbose_name = _('periodic task')
         verbose_name_plural = _('periodic tasks')
+        indexes = [CeleryMySQLIndex(fields=['name'])]
 
     def validate_unique(self, *args, **kwargs):
         super(PeriodicTask, self).validate_unique(*args, **kwargs)

t/proj/settings.py

@@ -122,3 +122,4 @@
 # https://docs.djangoproject.com/en/1.9/howto/static-files/
 
 STATIC_URL = '/static/'
+DJANGO_CELERY_BEAT_NAME_MAX_LENGTH = 191