Build controller-based queries with Cratis Arc

A Cratis Arc controller-based query lets you read data through an ASP.NET Core MVC GET action and return Arc query results. Choose this approach when you want MVC routing, model binding, or authorization policies. The query method lives on the controller, separate from the returned type; a model-bound query keeps the method on the read model instead.

Start with an MVC GET action

The action below reads all accounts from a MongoDB collection and requires the AccountReader role. It uses the shared AccountId and AccountName concepts with an ASP.NET Core Arc host, MVC, and the configured Arc MongoDB provider. Use this DebitAccount declaration instead of the model-bound alternative. No Chronicle integration is required.

using System.Collections.Generic;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using MongoDB.Driver;

namespace Banking.Accounts;

public record DebitAccount(AccountId Id, AccountName Name, decimal Balance);

[Authorize(Roles = "AccountReader")]
[Route("api/accounts")]
public class AccountsController(IMongoCollection<DebitAccount> collection) : ControllerBase
{
    [HttpGet]
    public IEnumerable<DebitAccount> AllAccounts() => collection.Find(_ => true).ToList();
}

With authentication and authorization middleware configured, [Authorize] protects the action before it reads the collection. MVC binds the request arguments. Arc’s QueryActionFilter establishes the query context and checks MVC model state before allowing the action to run. The returned data passes through read-model interception and appears inside a QueryResult response with query metadata.

This MVC path uses an action filter, not the model-bound IQueryPipeline filter chain. Custom model-bound query filters do not run here. The Arc wrapper described above handles GET actions, so changing the verb to POST does not preserve that contract.

Choose the next step

• Route templates bind identifiers from route values.
• Query arguments accept scalar values, arrays, and MVC request objects.
• Dependency injection supplies storage and application services.
• Return types describe wrapping, nulls, and explicit MVC responses.
• Paging lets clients navigate an IQueryable<T> result.
• Observable queries keep clients updated through server-sent events or WebSocket.

After choosing the action’s arguments and return type, use the proxy generator to create client types from supported controller query declarations. If you need raw MVC responses, follow without wrappers and provide a client that understands that response shape. A standard Arc query client expects the Arc wrapper.