CreativeMinds CQSLight

A .NET library for simple command query separation, build for .NET 8+.

According to CQS, every method should either be a command that performs an action, or a query that returns data to the caller, but not both.

If you need to validate your commands or queries or check for authorisation, CreativeMinds CQSLight will handle that too, automatically. As per CQS, CreativeMinds CQSLight does not allow commands to return any data, so if any validation or permission check fail, an exception will be thrown.

Commands and queries will have their authorisers executed first, if any are present, then the validations, again if any are present, and finally the actual command or query will be executed.

Changes from CreativeMinds.CQS to CreativeMinds.CQSLight

We have decided to remove the need for a 3rd party library to handle dependency inject, so instead of letting the library figure out the handlers of the commands and query, you now use decorators on the query/command classes.

Only one CommandHandlerAttribute and QueryHandlerttribute is allowed per class. The types provided does have to implement either the ICommandHandler<TCommand> or IQueryHandler<TQuery, TResult> interfaces.

public class CreateForumCommandHandler : ICommandHandler<CreateForumCommand> {

	public Task HandleAsync(CreateForumCommand command, CancellationToken cancellationToken) {
		// ......
	}
}

public class FindActiveSalesQueryHandler : IQueryHandler<FindActiveSalesQuery, IEnumerable<Dtos.SaleBaseForList>> {

	public Task<IEnumerable<Dtos.SaleBaseForList>> HandleAsync(FindActiveSalesQuery query, CancellationToken cancellationToken) {
		// ......
	}
}

Validation

[CommandHandler(typeof(CreateForumCommandHandler))]
[Validator(typeof(CreateForumCommandValidator))]
public record CreateForumCommand : ICommand {
	public string Name {get;set;}
}

By adding the ValidatorAttribute to your command/query classes, they will be validated be the given validators before being executed.

public class CreateForumValidator : IValidator<CreateForumCommand> {

	public Task<ValidationResult> Validate(CreateForumCommand command, CancellationToken cancellationToken) {
		// ......
	}
}

You can add any number of validators for the same command/query.

Authorisation

[QueryHandler(typeof(FindActiveSalesQueryHandler))]
[Authoriser(typeof(FindActiveSalesQueryAuthoriser))]
public record FindActiveSalesQuery : IQuery<IEnumerable<Dtos.SaleBaseForList>> { }

By adding the AuthoriserAttribute to your command/query classes, they will be checked before being executed.

public class FindActiveSalesQueryAuthoriser : IAuthoriser<FindActiveSalesQuery> {

		protected Task<AuthorisationResult> AuthoriseAsync(FindActiveSalesQuery command, CancellationToken cancellationToken) {
			// .....
		}
}

You can add one or more authorisers for each command/query.

Dispatching commands and queries

When you need to call the code of a command or a query, all you need to do is get a hold of an ICommandDispatcher or an IQueryDispatcher and dispatch the command/query.

public SaleController(ICommandDispatcher commandDispatcher, IQueryDispatcher queryDispatcher) {
	this.commandDispatcher = commandDispatcher ?? throw new ArgumentNullException(nameof(commandDispatcher));
	this.queryDispatcher = queryDispatcher ?? throw new ArgumentNullException(nameof(queryDispatcher));
}

[HttpPut("{saleId}/{bidId}/accept")]
public async Task<IActionResult> AcceptBidAsync(String saleId, String bidId, CancellationToken cancellationToken) {
	// A command does not return anything, so unless an exception is throw, everything went according to the plan!
	await this.commandDispatcher.DispatchAsync<AcceptBidCommand>(new AcceptBidCommand { SaleId = saleId, BidId = bidId }, cancellationToken);
	return Ok();
}

[AllowAnonymous]
[HttpGet]
public async Task<IEnumerable<Dtos.SaleBaseForList>> GetSalesAsync(CancellationToken cancellationToken) {
	return await this.queryDispatcher.DispatchAsync<FindActiveSalesQuery, IEnumerable<Dtos.SaleBaseForList>>(new FindActiveSalesQuery { PageIndex = 0 }, cancellationToken);
}

CreativeMinds CQSLight Dependency Injection

Unlike CreativeMinds.CQS, CreativeMinds.CQSLight uses the build-in dependency injection of .NET, and does not need a 3rd party library.

All you need to do, is add the handlers, validators and authorisers using the AddCQS method with the assemblies where the CQS code is.

builder.Services.AddCQS(typeof(Program).Assembly);