Send commands, fetch queries, and broadcast events using a mediator pattern for CQRS+ES
For the last few years, Command Query Responsibility Segregation (CQRS) and Event Sourcing (ES) emerged as patterns that can help implement large scale systems, with some risky complexity, by having different models to read or mutate data while also using events as a single source of truth.
Since there are already great articles explaining CQRS or ES in great depth, I’m going to focus and show how you can decouple your application layers by only knowing POCOs and a mediator instance from SimpleSoft.Mediator.
Remember that, even if you are not using CQRS or ES to its full extend, just by…
Audit commands and store events with transversal behavior
When implementing a web application, it can be a good idea to enforce some kind of auditing to all of your client interactions, either to track their behavior over time, to ensure any security breach will be properly logged, or just to help analyze system bugs.
Previously we talked about using the mediator pattern to implement the Command Query Responsibility Segregation (CQRS) and Event Sourcing (ES) and how pipelines could be used to implement transversal behavior to your application.
Since commands are responsible to mutate the system state, in this article I’m going to demonstrate how you could implement an…
Manage Entity Framework Core transactions when handling commands
When implementing a simplified CQRS service, which usually has a single database but still separates commands from queries, the mediator pipeline can be used to manage transactions when processing commands, ensuring changes will be implicitly committed unless an exception is thrown.
Implementing a pipeline for transactions has some key advantages even when using Entity Framework Core or other ORM that tracks and flushes changes at a single point in time.
Because the command handler is executing inside an implicit transaction, the developer is free to flush their changes as it sees fit knowing that any exception will rollback the changes…
Validate commands, events or queries with transversal behavior
When implementing web applications that manipulate information, there is always the need to validate data sent by the clients, ensuring business rules are properly implemented.
Previously I talked about the implementation of Command Query Responsibility Segregation (CQRS) and Event Sourcing (ES) using a mediator pattern and how to support transversal behavior via pipelines.
In this article I’m going to demonstrate how validation can be enforced into your commands and events before reaching the handlers, making sure that invalid data will be rejected by the API.
This approach not only reduces the amount of duplicated code, it also ensures validations won’t…
Intercept commands, queries and events to apply transversal behavior
In my previous article I explained how you could implement Command Query Responsibility Segregation (CQRS) and Event Sourcing (ES) patterns using a mediator instance from SimpleSoft.Mediator in ASP.NET Core applications.
This time I’m going to explain how to intercept commands, queries and events, making it possible to apply transversal behavior before they reach the handlers, reducing significantly the amount of boilerplate and duplicated code.
Transaction management, logging, auditing, caching or validations are some of the good examples where pipelines can be very helpful. Imagine the following chains:
Commands: Mediator
LoggingPipeline
ValidationPipeline
TransactionPipeline
AuditPipeline
HandlerQueries: Mediator
LoggingPipeline
HandlerEvents:…
Adding support for Dependency Injection, Logging and Configurations using the NuGet SimpleSoft.Hosting
Life as a .NET developer never looked brighter and more exciting. This last few years have been amazing: .NET Standard, ASP.NET Core, oficial Linux and Mac support, open source everywhere, what more can we ask? Well, one thing that always seems to be forgotten are console application, despite their important role.
In this article I’ll explain how can someone create more complex or fasten the development of console applications by using a small library named SimpleSoft.Hosting.
Why complex console applications?
Ever since I entered the .NET world, my main focus was on all sorts of web applications, but over time I also found console…
Simplifying the exception handling of ASP.NET Core MVC applications by using the NuGet SimpleExceptionHandling
Nowadays, when someone talks about web development in the .NET world, it is almost certain to be talking about ASP.NET MVC, ASP.NET Web API or, the more recently released, ASP.NET Core MVC. These are frameworks developed by Microsoft to help the development of server side logic for web applications.
In this article I’ll explain how can someone simplify the global handling of exceptions based on their type or properties by using a small library named Simple Exception Handling in ASP.NET Core MVC applications.
Exception handling in ASP.NET Core MVC
Exceptions, despite being rare, are an important aspect that any developer should be aware when creating applications…
João Simões
Solutions Architect trying to solve world “problems”!
