Django

BemiHQ/bemi-django

Bemi plugs into Django and PostgreSQL to track database changes automatically. It unlocks robust context-aware audit trails and time travel querying inside your application.

This Python package is a recommended Django integration, enabling you to pass application-specific context when performing database changes. This can include context such as the 'where' (API endpoint, worker, etc.), 'who' (user, cron job, etc.), and 'how' behind a change, thereby enriching the information captured by Bemi.

See this example repo as a Django Todo app that automatically tracks and contextualized all changes.

Prerequisites

PostgreSQL 14+
Django

Installation

Install the Python package

pip install bemi-django

Add bemi app to your Django project's INSTALLED_APPS

settings.py
INSTALLED_APPS = [
    # Your other apps
    'bemi',
]

Run the migration add lightweight PostgreSQL triggers for passing application context with all data changes into PostgreSQL replication log

python manage.py migrate bemi

Usage

Add the Bemi middleware to your Django project app and add the path to a custom get_bemi_context function to automatically pass application context with all tracked database changes made within an HTTP request:

settings.py
MIDDLEWARE = [
    # Your other middlewares
    'bemi.BemiMiddleware',
]

BEMI_CONTEXT_FUNCTION = 'your_project.utils.get_bemi_context'

Now you can easily specify custom application context:

your_project/utils.py

def get_bemi_context(request):
    # Return any custom context dict
    return {
      'user_id': request.user.id,
      'method': request.method,
      'path': request.path,
    }

Application context:

Is bound to the current execution thread within an HTTP request.
Is used only with INSERT, UPDATE, DELETE SQL queries performed via Django. Otherwise, it is a no-op.
Is passed directly into PG Write-Ahead Log with data changes without affecting the structure of the database and SQL queries.

Application context will automatically include the original SQL query that performed data changes, which is generally useful for troubleshooting purposes.

Data change tracking

Local database

To test data change tracking and the Django integration with a locally connected PostgreSQL, you need to set up your local PostgreSQL.

First, make sure your database has SHOW wal_level; returning logical. Otherwise, you need to run the following SQL command:

-- Don't forget to restart your PostgreSQL server after running this command
ALTER SYSTEM SET wal_level = logical;

To track both the "before" and "after" states on data changes, please run the following SQL command:

ALTER TABLE [YOUR_TABLE_NAME] REPLICA IDENTITY FULL;

Then, run a Docker container that connects to your local PostgreSQL database and starts tracking all data changes:

docker run \
  -e DB_HOST=host.docker.internal \
  -e DB_PORT=5432 \
  -e DB_NAME=[YOUR_DATABASE] \
  -e DB_USER=postgres \
  -e DB_PASSWORD=postgres \
  public.ecr.aws/bemi/dev:latest

Replace DB_NAME with your local database name. Note that DB_HOST pointing to host.docker.internal allows accessing 127.0.0.1 on your host machine if you run PostgreSQL outside Docker. Customize DB_USER and DB_PASSWORD with your PostgreSQL credentials if needed.

Now try making some database changes. This will add a new record in the changes table within the same local database after a few seconds:

psql postgres://postgres:[email protected]:5432/[YOUR_DATABASE] -c \
  'SELECT "primary_key", "table", "operation", "before", "after", "context", "committed_at" FROM changes;'

 primary_key | table | operation |                       before                       |                       after                         |                        context                                                            |      committed_at
-------------+-------+-----------+----------------------------------------------------+-----------------------------------------------------+-------------------------------------------------------------------------------------------+------------------------
 26          | todo  | CREATE    | {}                                                 | {"id": 26, "task": "Sleep", "is_completed": false}  | {"user_id": 187234, "endpoint": "/todo", "method": "POST", "SQL": "INSERT INTO ..."}      | 2023-12-11 17:09:09+00
 27          | todo  | CREATE    | {}                                                 | {"id": 27, "task": "Eat", "is_completed": false}    | {"user_id": 187234, "endpoint": "/todo", "method": "POST", "SQL": "INSERT INTO ..."}      | 2023-12-11 17:09:11+00
 28          | todo  | CREATE    | {}                                                 | {"id": 28, "task": "Repeat", "is_completed": false} | {"user_id": 187234, "endpoint": "/todo", "method": "POST", "SQL": "INSERT INTO ..."}      | 2023-12-11 17:09:13+00
 26          | todo  | UPDATE    | {"id": 26, "task": "Sleep", "is_completed": false} | {"id": 26, "task": "Sleep", "is_completed": true}   | {"user_id": 187234, "endpoint": "/todo/complete", "method": "PUT", "SQL": "UPDATE ..."}   | 2023-12-11 17:09:15+00
 27          | todo  | DELETE    | {"id": 27, "task": "Eat", "is_completed": false}   | {}                                                  | {"user_id": 187234, "endpoint": "/todo/27", "method": "DELETE", "SQL": "DELETE FROM ..."} | 2023-12-11 17:09:18+00

Remote database

Go to Bemi.io Dashboard UI and follow the instructions to connect your hosted PostgreSQL database in a few seconds.

dashboard

Once the project infrastructure is provisioned, it'll automatically ingest and store all data changes stitched with an application context in a separate serverless PostgreSQL database. You can test the connection by running the following command:

psql postgres://[USERNAME]@[HOSTNAME]:5432/[DATABASE] -c \
  'SELECT "primary_key", "table", "operation", "before", "after", "context", "committed_at" FROM changes;'

 primary_key | table | operation |                       before                       |                       after                         |                        context                                                            |      committed_at
-------------+-------+-----------+----------------------------------------------------+-----------------------------------------------------+-------------------------------------------------------------------------------------------+------------------------
 26          | todo  | CREATE    | {}                                                 | {"id": 26, "task": "Sleep", "is_completed": false}  | {"user_id": 187234, "endpoint": "/todo", "method": "POST", "SQL": "INSERT INTO ..."}      | 2023-12-11 17:09:09+00
 27          | todo  | CREATE    | {}                                                 | {"id": 27, "task": "Eat", "is_completed": false}    | {"user_id": 187234, "endpoint": "/todo", "method": "POST", "SQL": "INSERT INTO ..."}      | 2023-12-11 17:09:11+00
 28          | todo  | CREATE    | {}                                                 | {"id": 28, "task": "Repeat", "is_completed": false} | {"user_id": 187234, "endpoint": "/todo", "method": "POST", "SQL": "INSERT INTO ..."}      | 2023-12-11 17:09:13+00
 26          | todo  | UPDATE    | {"id": 26, "task": "Sleep", "is_completed": false} | {"id": 26, "task": "Sleep", "is_completed": true}   | {"user_id": 187234, "endpoint": "/todo/complete", "method": "PUT", "SQL": "UPDATE ..."}   | 2023-12-11 17:09:15+00
 27          | todo  | DELETE    | {"id": 27, "task": "Eat", "is_completed": false}   | {}                                                  | {"user_id": 187234, "endpoint": "/todo/27", "method": "DELETE", "SQL": "DELETE FROM ..."} | 2023-12-11 17:09:18+00

See Destination Database for more details.

Data change querying

Lastly, connect to the Bemi PostgreSQL destination database to easily query change data from your application.

To query historical data, configure an additional database connection:

django/todo_project/settings.py
DATABASES = {
    'default': ...
    'bemi': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': os.getenv('DESTINATION_DB_DATABASE'),
        'USER': os.getenv('DESTINATION_DB_USERNAME'),
        'PASSWORD': os.getenv('DESTINATION_DB_PASSWORD'),
        'HOST': os.getenv('DESTINATION_DB_HOST'),
        'PORT': os.getenv('DESTINATION_DB_PORT'),
    }
}

DATABASE_ROUTERS = ['bemi.BemiDatabaseRouter']

Add inheritance to a tracked models or query directly with BemiChange model.

django/todos/models.py
class Todo(BemiRecordMixin, models.Model):
  ...

Query changes

from bemi.models import BemiChange

BemiChange.objects.last()
# => <BemiChange: BemiChange object (cd9651ff-e378-41f7-add0-c4fdfa1575ae)>
#  id: "cd9651ff-e378-41f7-add0-c4fdfa1575ae",
#  committed_at: Tue, 25 Apr 2024 22:15:50.890000000 UTC +00:00,
#  table: "todos",
#  primary_key: "27",
#  operation: "UPDATE",
#  before: {"id"=>27, "task"=>"Walk", "is_completed"=>false}>
#  after: {"id"=>27, "task"=>"Run", "is_completed"=>true},
#  context:
#   {"SQL"=> "UPDATE \"public\".\"todos\" SET \"task\" = $1, \"is_completed\" = $2 WHERE \"public\".\"todos\".\"id\" = $3",
#    "user_id"=>1,
#    "api_endpoint"=>"/todos/complete"},
#  ...

Diff changed values

from bemi.models import BemiChange

BemiChange.objects.last().diff()
# => { "task" => ["Walk", "Run"], "completed" => [false, true] }

Query change by record

from todos.models import Todo

record = Todo.objects.get(pk=...)
record.bemi_changes()

Query by field

from todos.models import Todo
from bemi.models import BemiChange

# Last change that impacted the "task" field
record.bemi_changes(field_name='task').last()
BemiChange.objects.field_changed(table='todos', primary_key='cd9651ff-e378-41f7-add0-c4fdfa1575ae', field_name='task').last()

Filter by values

# Query by the previous values
record.bemi_changes().before({'task': 'Walk'})
record.bemi_changes().before({'task': 'Walk', 'completed': false})
record.bemi_changes().before_not({'task': 'Run'})

# Query by the new values
record.bemi_changes().after('task': 'Run')
record.bemi_changes().after('task': 'Run', 'completed': true)
record.bemi_changes().after_not('task': 'Walk')

# Query by the context values
record.bemi_changes().context({'user_id': 1})
record.bemi_changes().context({'user_id': 1, 'api_endpoint': '/tasks/complete'})
record.bemi_changes().context_not({'user_id': 123})

# Chain methods
record.bemi_changes.before({'task': 'Walk'}).after({'task': 'Run'})

Filter by operation

record.bemi_changes().created()
record.bemi_changes().updated()
record.bemi_changes().deleted()

Sort changes

record.bemi_changes().asc()
record.bemi_changes().desc()

Build a custom query

changes = BemiChange.objects.
  .filter(table='todos', operation='UPDATE')
  .filter(context__contains={"user_id": 1})
  .order_by('-committed_at')
  [:10]

License

Distributed under the terms of the LGPL-3.0. If you need to modify and distribute the code, please release it to contribute back to the open-source community. hide_title: true

Django

Prerequisites​

Installation​

Usage​

Data change tracking​

Local database​

Remote database​

Data change querying​

Query changes​

Diff changed values​

Query change by record​

Query by field​

Filter by values​

Filter by operation​

Sort changes​

Build a custom query​

License​