Metadata-Version: 2.1
Name: django-cqrs
Version: 1.4.0
Summary: Django CQRS data synchronisation
Home-page: http://connect.cloudblue.com
Author: CloudBlue
License: Apache License, Version 2.0
Description: Django CQRS
        ===========
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        `django-cqrs` is an Django application, that implements CQRS data synchronisation between several Django microservices.
        
        
        CQRS
        ----
        In Connect we have a rather complex Domain Model. There are many microservices, that are [decomposed by subdomain](https://microservices.io/patterns/decomposition/decompose-by-subdomain.html) and which follow [database-per-service](https://microservices.io/patterns/data/database-per-service.html) pattern. These microservices have rich and consistent APIs. They are deployed in cloud k8s cluster and scale automatically under load. Many of these services aggregate data from other ones and usually [API Composition](https://microservices.io/patterns/data/api-composition.html) is totally enough. But, some services are working too slowly with API JOINS, so another pattern needs to be applied.
        
        The pattern, that solves this issue is called [CQRS - Command Query Responsibility Segregation](https://microservices.io/patterns/data/cqrs.html). Core idea behind this pattern is that view databases (replicas) are defined for efficient querying and DB joins. Applications keep their replicas up to data by subscribing to [Domain events](https://microservices.io/patterns/data/domain-event.html) published by the service that owns the data. Data is [eventually consistent](https://en.wikipedia.org/wiki/Eventual_consistency) and that's okay for non-critical business transactions.
        
        
        Examples
        ========
        
        Integration
        -----------
        * Setup `RabbitMQ`
        * Install `django-cqrs`
        * Apply changes to master service, according to RabbitMQ settings
        ```python
        # models.py
        
        from django.db import models
        from dj_cqrs.mixins import MasterMixin, RawMasterMixin
        
        
        class Account(MasterMixin, models.Model):
            CQRS_ID = 'account'
            CQRS_PRODUCE = True  # set this to False to prevent sending instances to Transport
            
            
        class Author(MasterMixin, models.Model):
            CQRS_ID = 'author'
            CQRS_SERIALIZER = 'app.api.AuthorSerializer'
        
        
        # For cases of Diamond Multiinheritance the following approach could be used:
        from mptt.models import MPTTModel
        from dj_cqrs.metas import MasterMeta
        
        class ComplexInheritanceModel(MPTTModel, RawMasterMixin):
            pass
        
        MasterMeta.register(ComplexInheritanceModel)
        ```
        
        ```python
        # settings.py
        
        CQRS = {
            'transport': 'dj_cqrs.transport.rabbit_mq.RabbitMQTransport',
            'host': RABBITMQ_HOST,
            'port': RABBITMQ_PORT,
            'user': RABBITMQ_USERNAME,
            'password': RABBITMQ_PASSWORD,
        }
        
        ```
        * Apply changes to replica service, according to RabbitMQ settings
        ```python
        from django.db import models
        from dj_cqrs.mixins import ReplicaMixin
        
        
        class AccountRef(ReplicaMixin, models.Model):
            CQRS_ID = 'account'
            
            id = models.IntegerField(primary_key=True)
            
        
        class AuthorRef(ReplicaMixin, models.Model):
            CQRS_ID = 'author'
            CQRS_CUSTOM_SERIALIZATION = True
            
            @classmethod
            def cqrs_create(cls, sync, **mapped_data):
                # Override here
                pass
                
            def cqrs_update(self, sync, **mapped_data):
                # Override here
                pass
        ```
        
        ```python
        # settings.py
        
        CQRS = {
            'transport': 'dj_cqrs.transport.RabbitMQTransport',
            'queue': 'account_replica',
            'host': RABBITMQ_HOST,
            'port': RABBITMQ_PORT,
            'user': RABBITMQ_USERNAME,
            'password': RABBITMQ_PASSWORD,
        }
        ```
        * Apply migrations on both services
        * Run consumer worker on replica service. Management command: `python manage.py cqrs_consume -w 2`
        
        Notes
        -----
        
        When there are master models with related entities in CQRS_SERIALIZER, it's important to have operations within atomic transactions.
        CQRS sync will happen on transaction commit. Please, avoid saving master model within transaction more then once to reduce syncing and potential racing on replica side.
        Updating of related model won't trigger CQRS automatic synchronization for master model. This needs to be done manually.
        
        Example:
        ```python
        with transaction.atomic():
            publisher = models.Publisher.objects.create(id=1, name='publisher')
            author = models.Author.objects.create(id=1, name='author', publisher=publisher)
        
        with transaction.atomic():
            publisher.name = 'new'
            publisher.save()
        
            author.save()
        ```
        
        When only needed instances need to be synchronized, there is a method `is_sync_instance` to set filtering rule. 
        It's important to understand, that CQRS counting works even without syncing and rule is applied every time model is updated.
        
        Example:
        ```python
        
        class FilteredSimplestModel(MasterMixin, models.Model):
            CQRS_ID = 'filter'
        
            name = models.CharField(max_length=200)
        
            def is_sync_instance(self):
                return len(str(self.name)) > 2
        ```
        
        
        Utilities
        ---------
        Bulk synchronizer without transport (usage example: it may be used for initial configuration). May be used at planned downtime.
        * On master service: `python manage.py cqrs_bulk_dump --cqrs-id=author` -> `author.dump`
        * On replica service: `python manage.py cqrs_bulk_load -i=author.dump`
        
        Filter synchronizer over transport (usage example: sync some specific records to a given replica). Can be used dynamically.
        * To sync all replicas: `python manage.py cqrs_sync --cqrs-id=author -f={"id__in": [1, 2]}`
        * To sync all instances only with one replica: `python manage.py cqrs_sync --cqrs-id=author -f={} -q=replica`
        
        Set of diff synchronization tools ()
        * To get diff and synchronize master service with replica service in K8S: 
        ```bash
        kubectl exec -i MASTER_CONTAINER -- python manage.py cqrs_diff_master --cqrs-id=author | 
            kubectl exec -i REPLICA_CONTAINER -- python manage.py cqrs_diff_replica |
            kubectl exec -i MASTER_CONTAINER -- python manage.py cqrs_diff_sync
        ```
        
        Development
        ===========
        
        1. Python 3.6+
        0. Install dependencies `requirements/dev.txt`
        
        Testing
        =======
        
        Unit testing
        ------
        1. Python 3.6+
        0. Install dependencies `requirements/test.txt`
        0. `export PYTHONPATH=/your/path/to/django-cqrs/`
        
        Check code style: `flake8`
        Run tests: `pytest`
        
        Tests reports are generated in `tests/reports`. 
        * `out.xml` - JUnit test results
        * `coverage.xml` - Coverage xml results
        
        To generate HTML coverage reports use:
        `--cov-report html:tests/reports/cov_html`
        
        
        Integrational testing
        ------
        1. docker-compose
        0. `cd integration_tests`
        0. `docker-compose run master`
Keywords: django cqrs sql mixin amqp
Platform: UNKNOWN
Classifier: Development Status :: 5 - Production/Stable
Classifier: Framework :: Django :: 1.11
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: Apache Software License
Classifier: Operating System :: Unix
Classifier: Programming Language :: Python :: 3.6
Classifier: Programming Language :: Python :: 3.7
Classifier: Programming Language :: Python :: 3.8
Classifier: Topic :: Communications
Classifier: Topic :: Database
Requires-Python: >=3.6
Description-Content-Type: text/markdown
