CQRS Pattern

The Command and Query Responsibility Segregation (CQRS) pattern separates read and update operations for a data store. Implementing CQRS in your application can maximize its performance, scalability, and security.

How?

• Commands should be task based, rather than data centric. ("Place Order").

• Commands may be placed on a queue for asynchronous processing, rather than being processed synchronously.

• Queries never modify the database. A query returns a DTO that does not encapsulate any domain knowledge.

• For greater isolation, the data-stores are physically separate the read data from the write data.

• The data-sync between write and read database is done using master-slave replication on mysql, however the same can be achieved using ETL tools or Mule Batch programs as well.

A note of caution:

• This pattern is not suitable if :-

  • The domain or the business rules are simple.

  • A simple CRUD-style operations are sufficient.

Usecase

• An ecommerce site or Mobile App which allows to place order and query order details.

• The write model of the order not not just the order header and order lines but also customer related information to be created, and this is based on Task UI

• The read model of the order is based on complex queries.

• The number of reads are very high compared to writes.

• Eventual consistency of data is acceptable

• The following usecase is implemented using Mule as follows:-

  

Dependencies

To run this example, you will need :-

• Mule(On-premise)
• RabbitMQ
• MYSQL

Setups

RabbitMQ

You can install it locally, using the following steps.

• For RabbitMQ installation instructions please follow the link below :-

https://www.rabbitmq.com/download.html

• After successful installation you should be able to run it Using

  export PATH=$PATH:/usr/local/opt/rabbitmq/sbin
  sudo rabbitmq-server

• To access Rabbit MQ use the following url :-

http://localhost:15672/

• Create Queues and Exchanges as per your configuration file.

• Create Order Exchange as direct :-

• Create Order Queue as follows :-

• Bind exchange to queue and verify it as follows :-

MYSQL (Docker)

• Create Docker Network using the following Command

docker network create groupnet

• Pull mysql docker image

docker pull mysql

• Create master database server. We are using groupnet network group for our docker container.

docker run -p 3306:3306 -p 33060:33060 --name mysql-server-master --net=groupnet  --hostname=mysql-server-master -v $PWD/mysql-server-master-share:/var/lib/mysql -e MYSQL_ROOT_PASSWORD=Password -d mysql --bind-address=172.18.0.2 --server-id=1

• Creating Slave Database server and setting up replication is optional as you can point cqrs-order-details-sys-api to point to Master to test our example.

• But If you really want to do it in a proper way continue as outlined in

  • MSQL-Replication.md https://github.com/kprabhureddy/cqrs-pattern/blob/master/MSQL-Replication.md

• Run the table creation scripts under docs/scripts folder to create the underlying tables (customer, order_header, order_lines). You can use SQLWorkbench tool to connect to MYSQL database and execute the script.

Contribution

PK Reddy

References

https://docs.microsoft.com/en-us/azure/architecture/patterns/cqrs

https://martinfowler.com/bliki/CQRS.html

Todos

None

License

UNLICENSED