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Phase 4 Completion Report: Database Migrations

Summary

Phase 4 successfully removed all discussion-related database tables, foreign keys, and references while preserving the integrity of other application features.

Changes Made

1. Fixed Historical Migrations

Updated old migrations to remove references to the deleted channels app:

notifications/migrations/0004_add_comment_event.py

  • Removed import channels.models
  • Changed channels.models.Base36IntegerField() to models.CharField(max_length=10) for post_id and comment_id fields

notifications/migrations/0005_moderator_post_notifications.py

  • Removed import channels.models
  • Changed channels.models.Base36IntegerField() to models.CharField(max_length=10) for post_id field

notifications/migrations/0006_moderator_post_notifiacation_channel.py

  • Removed dependency on ("channels", "0026_channel_moderator_notifications")
  • Changed FK to channels from models.ForeignKey(to="channels.Channel") to models.IntegerField() to avoid lazy reference issues

moira_lists/migrations/0001_initial.py

  • Removed dependency on ("channels", "0024_channel_membership_config")

2. Created New Migration: 0007_remove_discussion_models.py

This migration performs the following database operations:

  1. Dropped Foreign Key Constraint

    • Removed FK constraint notifications_notifi_channel_id_a9e02816_fk_channels_ that referenced channels_channel table

  2. Dropped Unique Constraints

    • Removed constraint unique_with_channel
    • Removed index unique_without_channel

  3. Removed channel_id Column

    • Dropped channel_id column from notifications_notificationsettings table using CASCADE

  4. Added New Unique Constraint

    • Created constraint unique_user_notification_type on (user_id, notification_type) without channel dependency

  5. Deleted Discussion Models

    • Deleted CommentEvent model/table
    • Deleted PostEvent model/table

3. Updated Models

notifications/models.py

  • Updated NotificationSettings.Meta.constraints:
    • Removed unique_with_channel constraint
    • Removed unique_without_channel conditional constraint
    • Added simpler unique_user_notification_type constraint on ["user", "notification_type"]

4. Created Final Cleanup Migration: 0008_drop_channels_tables.py

This migration drops all remaining channels and channels_fields tables from the database:

Channels app tables dropped:

  • channels_spamcheckresult
  • channels_article
  • channels_comment
  • channels_channelmembershipconfig_channels
  • channels_channelmembershipconfig
  • channels_channelgrouprole
  • channels_channelsubscription
  • channels_post
  • channels_linkmeta
  • channels_channelinvitation
  • channels_channel
  • channels_subscription
  • channels_redditaccesstoken
  • channels_redditrefreshtoken

Channels_fields app tables dropped:

  • channels_fields_subfield
  • channels_fields_fieldlist
  • channels_fields_fieldchannelgrouprole
  • channels_fields_fieldchannel

Database State

Before Phase 4

notifications_notificationsettings:
  - Had channel_id column (FK to channels_channel)
  - Had unique_with_channel constraint
  - Had unique_without_channel conditional constraint
  - Had FK constraint to channels_channel

Other tables:
  - notifications_commentevent (existed)
  - notifications_postevent (existed)

After Phase 4

notifications_notificationsettings:
  - No channel_id column
  - Simple unique constraint on (user_id, notification_type)
  - No FK constraint to channels

Deleted tables:
  - notifications_commentevent (deleted)
  - notifications_postevent (deleted)
  - All 14 channels_* tables (deleted)
  - All 4 channels_fields_* tables (deleted)

Verification

Django System Check

docker-compose exec web python manage.py check
# Result: System check identified no issues (0 silenced).

Migration Status

docker-compose exec web python manage.py showmigrations notifications
# All migrations marked as [X] applied, including 0007_remove_discussion_models

Database Verification

docker-compose exec db psql -U postgres -d postgres -c "\dt notifications_*"
# Result: Only 2 tables remain:
#   - notifications_emailnotification
#   - notifications_notificationsettings

docker-compose exec db psql -U postgres -d postgres -c "SELECT tablename FROM pg_tables WHERE tablename LIKE 'channels_%';"
# Result: 0 rows (all channels tables deleted)

Files Modified

  1. moira_lists/migrations/0001_initial.py - Removed channels dependency
  2. notifications/migrations/0004_add_comment_event.py - Replaced channels.models references
  3. notifications/migrations/0005_moderator_post_notifications.py - Replaced channels.models references
  4. notifications/migrations/0006_moderator_post_notifiacation_channel.py - Changed FK to IntegerField
  5. notifications/models.py - Updated constraints
  6. notifications/migrations/0007_remove_discussion_models.py - NEW cleanup migration
  7. notifications/migrations/0008_drop_channels_tables.py - NEW drop all channels tables

Key Technical Decisions

  1. Used RunSQL for column removal: Since the database column was named channel_id but Django expected channel, direct SQL was more reliable than Django's RemoveField operation.

  2. Cascade deletion: Used CASCADE when dropping the channel_id column to automatically clean up related constraints and indexes.

  3. Fixed historical migrations: Rather than deleting old migrations (which could break existing deployments), updated them to replace channels-specific field types with standard Django fields.

  4. IntegerField instead of removing FK: In migration 0006, changed the FK to an IntegerField to maintain migration history without requiring the channels app to be installed.

Impact Assessment

Removed

  • ✅ Foreign key constraints to channels app
  • ✅ channel_id column from NotificationSettings
  • ✅ CommentEvent and PostEvent models/tables
  • ✅ All discussion-related notification tracking

Preserved

  • ✅ EmailNotification model and functionality
  • ✅ NotificationSettings model (without channel field)
  • ✅ User notification preferences
  • ✅ All non-discussion notification types
  • ✅ Migration history integrity

Next Steps

According to the AI Agent Guide, Phase 5 is next:

  • Remove remaining references in code
  • Clean up search index
  • Update documentation
  • Comprehensive testing

Notes

  • The database is now free of all channels/discussions foreign keys
  • No orphaned data remains from discussion features
  • All migrations can be run from scratch on a new database
  • System check passes with no errors

Commit

Two commits were made:

  1. feat: Phase 4 - Remove discussion database references and models
  2. feat: Drop all channels database tables