In order to express what this query does we end up with a longer but more descriptive name for the query. Here’s what it would look like if we passed it in as a paramter:More generic and thus less methods needed, but less descriptive. The reason for this is that they are value objects and thus are immutable.
This is where Mediator pattern comes into picture: it encapsulates these interactions and takes care of the mapping for us.To implement CQRS using this pattern, we define a "Request" and a "Handler". Get started. We are constructing a expression based on an Employee type and returning an anonymous type. A CommandRequest to WRITE new Reader to the database looks like below.Observe that we have added a Property Model of type CreateReaderModel that holds the Reader information to be added to the database. Most apps these days are a front end like Angular hooked up to an API. This is how easy things get with swagger.We have covered CQRS implementation and definition, Mediator pattern and MediatR Library, Entity Framework Core Implementation, Swagger Integration, and much more. You can use Figure 8. My personal preference right now is to use extension methods on the aggregate root DbSet which I feel is more natural when working with EF Core and lends itself to a more functional paradigm. An application that offers something more than a basic CRUD operation over the dataset - which achieves something I did not fix the projections for what seem to be navigational properties, as I could not make that assumption without more context.And then fix the returning type not to be void (or, more specficially, `Task`).Writing against a DTO is more safe for refactoring and context. In the cases where a DTO makes sense, do everyone a favor and skip the horrible DTO suffix. Contact me to work directly. The main idea is that in the majority of cases you are not going to need to use a DTO and can just take your custom query and pass it back as JSON directly without needing a strongly typed query object to represent your data structure.Separating the projections is indeed helpful.
On the controller end, its a simple affair with only to create a CommandRequest request and Send on the Mediator.To wire up the Mediator DependencyInjection capabilities which we're using in to resolve dependencies at the Handler, we add the MediatR service to the container during the Startup as below:The type attribute passed is the location where the MediatR needs to check for resolving dependency related information. In our example this is going to be the Employee DbSet. If you are needing to modify the values before returning it, then I think that depends on your use case. CQRS may require a lot of code. This particular class will help us to access the data using Entity Framework Core ORM.Now that we have completed the class, let me show you an easy way to generate an Interface for any given class. Makes sense.The dynamic approach won’t work when you use auto generated clients through nswag I guess. In other words, you will end up with at least 3 or 4 times more code-lines than you usually would. These methods might require data validation or transformation before writing onto the database. In fact, if you want to pull out the full performance of Entity Framework Core, you need to avoid it wherever possible as I have written about Let’s start off by writing our projection. Thanks! We will dive deep into Mediator in another post.
The project relies on a REST-like application that handles customer information (basically user’s data and a list of phones) to demonstrate how a single model lives within a CQRS structure.The first thing you must install is the latest version of Visual Studio (the Community edition is good to go). It’s a design pattern that seperated the read and write operations, hence decoupling the solution to a great extend.No. Examples are POST, PUT or PATCH methods. In this artice, you will see a sample project implementation according to the CQRS pattern using MediatR in ASP.NET Core MVC with vue.js. Now, you need to create the database context that’ll command the rules of the migration. It also has the following additional benefits:I place my queries and commands in separate folders in the data project. It consists of a Web API, a REST web service that will deal with customers data in a CRUD fashion, however, sending each of the commands to its respective handler.
Applying CQRS on applications without a need would unnecessarily complicate the architecture which might result in an anti-pattern situations.CQRS should only be used when the application has characteristics like:Complex application model with multiple relationships and dependencies CQRS pattern will support this usage out of the box, you would not have to break your head trying to implement such a cache mechanism.Since we have dedicated models per oprtation, there is no possibility of data loss while doing parellel operations.The one thing that may concern a few programmers is that this is a code demanding pattern. With well written code, CQRS actually performs the data source calls in a better way.You should also run “Install-Package Microsoft.EntityFrameworkCore.Tools” in the Nuget package Manager Console in order to be able to generate the migrations.Yes, I believe this package is included by default while installing the other EF Core packages on ASP.NET Core Applications. Various connection string formats can be found Here is what you would add to your appsettings.json.Now we have our models and the connection string ready, all we have to do is to generate a database from the defined models. Can you expand into Event Store with EF?Hi Oded, thanks for reading, and sorry for the late reply. The Handler makes use of these public Properties to get the data. We will need to connect a data source to the API. The Handler transforms the data into required projection so that the domain data is encapsulated from unwanted access.Observe that the methods which WRITE to the database and which READ from the database use separate data representations: CreateReaderModel or UserRequestModel and ReaderResponseModel and UserResponseModel.