feat: Optimize the querying of course block dates when querying dates…

… for use in a

course outline, which don't need block dates below the subsection level of a course.
Also, rework the block date caching to use TieredCache, as well as using the current
published version of a course in the cache key to remove the need for cache invalidation.

TNL-8061

CHANGELOG.rst

@@ -14,6 +14,11 @@ Change Log
 Unreleased
 ~~~~~~~~~~
 
+[2.2.0] - 2021-08-27
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+* Added optimization when requesting course block dates for an outline, where block dates below subsections are unneeded.
+* Use current version of the course to improve the cache key, along with using the TieredCache to cache date data.
+
 [2.1.0] - 2021-07-23
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Added Django 3.2 Support

edx_when/__init__.py

@@ -1,7 +1,7 @@
 """
-Your project description goes here.
+Central source of course block dates for the LMS.
 """
 
-__version__ = '2.1.0'
+__version__ = '2.2.0'
 
 default_app_config = 'edx_when.apps.EdxWhenConfig'  # pylint: disable=invalid-name

edx_when/migrations/0008_courseversion_block_type.py

@@ -0,0 +1,54 @@
+# Generated by Django 3.2.6 on 2021-08-31 13:55
+
+import django.db.models.deletion
+import opaque_keys.edx.django.models
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('edx_when', '0007_meta_tweaks'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='CourseVersion',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('published_version', models.CharField(max_length=255)),
+            ],
+        ),
+        migrations.AddField(
+            model_name='contentdate',
+            name='block_type',
+            field=models.CharField(max_length=255, null=True),
+        ),
+        migrations.AlterField(
+            model_name='contentdate',
+            name='course_id',
+            field=opaque_keys.edx.django.models.CourseKeyField(max_length=255),
+        ),
+        migrations.AlterField(
+            model_name='contentdate',
+            name='location',
+            field=opaque_keys.edx.django.models.UsageKeyField(default=None, max_length=255, null=True),
+        ),
+        migrations.AddIndex(
+            model_name='contentdate',
+            index=models.Index(fields=['course_id', 'block_type'], name='edx_when_course_block_type_idx'),
+        ),
+        migrations.AddIndex(
+            model_name='contentdate',
+            index=models.Index(fields=['course_id'], name='edx_when_course_id_idx'),
+        ),
+        migrations.AddIndex(
+            model_name='contentdate',
+            index=models.Index(fields=['location'], name='edx_when_location_idx'),
+        ),
+        migrations.AddField(
+            model_name='contentdate',
+            name='course_version',
+            field=models.ForeignKey(null=True, on_delete=django.db.models.deletion.CASCADE, to='edx_when.courseversion'),
+        ),
+    ]

edx_when/models.py

@@ -84,30 +84,47 @@ def clean(self):
             raise ValidationError(_("Absolute and relative dates cannot both be used"))
 
 
+class CourseVersion(models.Model):
+    """
+    Stores published versions of a course. Used to more easily cache the block dates.
+
+    .. no_pii:
+    """
+
+    published_version = models.CharField(max_length=255, blank=False)
+
+
 class ContentDate(models.Model):
     """
     Ties a DatePolicy to a specific piece of course content. (e.g. a due date for a homework).
 
     .. no_pii:
     """
 
-    course_id = CourseKeyField(db_index=True, max_length=255)
+    course_id = CourseKeyField(max_length=255)
     policy = models.ForeignKey(DatePolicy, on_delete=models.CASCADE)
-    location = UsageKeyField(null=True, default=None, db_index=True, max_length=255)
+    location = UsageKeyField(null=True, default=None, max_length=255)
     field = models.CharField(max_length=255, default='')
     active = models.BooleanField(default=True)
+    block_type = models.CharField(max_length=255, null=True)
+    course_version = models.ForeignKey(CourseVersion, null=True, on_delete=models.CASCADE)
 
     class Meta:
         """Django Metadata."""
 
         unique_together = ('policy', 'location', 'field')
+        indexes = [
+            models.Index(fields=('course_id', 'block_type'), name='edx_when_course_block_type_idx'),
+            models.Index(fields=['course_id'], name='edx_when_course_id_idx'),
+            models.Index(fields=['location'], name='edx_when_location_idx'),
+        ]
 
     def __str__(self):
         """
         Get a string representation of this model instance.
         """
         # Location already holds course id
-        return f'{self.location}, {self.field}'
+        return f'ContentDate({self.policy}, {self.location}, {self.field}, {self.block_type})'
 
     def schedule_for_user(self, user):
         """