Overview

Concepts

Squidex is implemented based on the following concepts:

CQRS

CQRS stands for Command Query Responsibility Segregation. It's a pattern that was first described by Greg Young. At its heart is the idea that you can use a different model to update information than the model you use to read information. Typical yo use event sourcing as the primarily source of truth for your data and then you subscribe to the events to create read models that can be used to query and fetch information about your entities.

Read more from Martin Fowler

Event Sourcing

We can query an application's state to find out the current state of the world, and this answers many questions. However there are times when we don't just want to see where we are, we also want to know how we got there.

Event Sourcing ensures that all changes to application state are stored as a sequence of events. Not just can we query these events, we can also use the event log to reconstruct past states, and as a foundation to automatically adjust the state to cope with retroactive changes.

A traditional representation of database state can be entirely recreated by reprocessing this event log. Event sourcing's benefits include strong auditing, creation of historic state, and replaying of events for debugging and analysis. Event sourcing has been around for a while, but we think it is used much less than it should be.

Although this approach adds a lot of complexity to the system it also has a lot of advantages:

  1. You have a history of all your changes.

  2. You can consume the events to create your custom storages, e.g. you can use the Elastic Search Stack for full text search or statistics.

  3. We never delete data and even for bigger bugs we can provide fixes that restore all your content.

  4. We don't have to care about data migration when we change the read models with a new version; you just have to run the event consumers from the beginning to populate the read store with the updated data.

Frameworks and Tools

Squidex is based on the following frameworks and tools:

  • ASP.NET Core for the backend.

  • Angular for the Management UI

  • MongoDB for the event Store and persistency

  • Orleans as a backend technology.

Of course we use a dozens of external dependencies, because we do not want to reinvent the wheel, but it would just be too much to list them here.

Slides about the current architecture (June 2019): https://www.slideshare.net/secret/yUk1EmYlw8pLZF