Simplify error handling and improve code readability with the Result Pattern

Get Started

Install nuget package using .Net CLI

or nuget using Nuget package manager GUI by searching DeepCode.Return

dotnet add package DeepCode.Return --version 1.0.1

How To Use

Define method return type with Return struct with TResult type parameter

TResult is type of the return

namespace Invoicing.Application.Orders.Commands.CreateOrderCommand;

internal class CreateOrderCommandHandler : IRequestHandler<CreateOrderCommand, Return<Order>>
{
    public async Task<Return<Order>> Handle(CreateOrderCommand request, CancellationToken cancellationToken)
    {
        Order order;
        //order creation logic
        return order;
    }
}

for non async methods

public Return<Order> CreateOrder(CreateOrder request, CancellationToken cancellationToken)
{
    Order order;

    //order creation logic
    return order;
}

Return struct can be used when there's no return value but to notify if function was success or not

public Return SendEmail()
{
    return Return.Success();
}

How to extract if state is success

Return<Order> orderCreateResult = CreateOrder(request, cancellationToken);
if(orderCreateResult.IsFailure)
{
// Failure code goes here
}
Order order = orderCreateResult.Value;
// success path here

Error Handling

Notify caller error with in built error types

Handle Conflicts,

 public Return<Order> CreateOrder(double totalAmount)
 {
     // logic to apply the discount if total amount is > 100
     // Inventory says out of stock due to high demand

     if (!inventoryManagement.AreEnoughStokesAvailable())
     {
          return Fault.Conflict("Not enough stockes in inventory.");
          //or
          return Return<Order>.Failure(Conflict.Create("Not enough stockes in inventory."));
     }

 }

Other in-built error type available

// all these take one string message arg and optinal description arg
return Fault.NotFound();
return Fault.InternalError();
return Fault.ReturnError();

Type check errors for decision making

Return<Order> result = GetOrder(id);

if(result.IsFailure)
{

    if(result.IsErrorTypeOf<NotFound>())
    {
    // Not found logic goes here.
    }

    if(result.ErrorsContain<NotFound>())
    {
    // if error list contains Not found logic goes here.
    }

    if(result.Error.Is<Unauthorized>())
    {
    // Unauthorize logic goes here.
    }

    if(result.Errors.ContainsErrorType<NotFound>())
    {
    // Not found logic goes here.
    }

    if(result.Errors.ContainsErrorType<OrderCreateError>())
    {
    // if custom error type
    }

}

Handle Errors from caller method

     Return<Order> orderCreateResult = CreateOrder(100);

     if (orderCreateResult.IsFailure)
     {
         // First error or only error of the list.
         Fault error = orderCreateResult.Error;

         // Read all errors returned.
         IReadOnlyList<Fault> errors = orderCreateResult.Errors;

         // Error logic goes here
     }

     if (orderCreateResult.IsFailure)
     {
         // Pass errors to call stack
         return orderCreateResult.Errors.ToList();
     }
 

Define custom error types

Need to be inherited from Fault record

public record OrderCreationErrors : Fault
{
    public OrderCreationErrors(string message, string? description = null) : base(message, description) { }

    public static OrderCreationErrors InvalidCustomerIdForOrderCreation =>
        new OrderCreationErrors("Could not find matching customer to the given customerId.");

    public static OrderCreationErrors CustomerBlacklisted =>
        new OrderCreationErrors("Customer with the given customerId has been blacklisted.");
}

Using Match

Match method can be used to trigger actions when some return is success or failure.

Trigger actions with no return type.

Return<Order> orderCreateResult = CreateOrder(100);

orderCreateResult.Match(
    onSuccess: (value) => _logger.Info($"{value.Id} Order created successfully."),
    onFailure: (errors) => _logger.Error("Failed to create order.")
    );

//Match first error of errors if failure.
orderCreateResult.MatchFirst(
    onSuccess: (value) => _logger.Info($"{value.Id} Order created successfully."),
    onFailure: (error) => _logger.Error("Failed to create order.")
    );

orderCreateResult.MatchAsync(
    onSuccess: async (value) =>
    {
        // Simulating async process
        await Task.Delay(100);
        _logger.Info($"{value.Id} Order created successfully.");
    },
    onFailure: async (errors) =>
    {
        // Simulating async process
        await Task.Delay(100);
        _logger.Error("Failed to create order.");
    });

Match using TNextValue type, has return after match

 Return<Order> orderCreateResult = Return<Order>.Success(new Order());

 Response<Order> response = orderCreateResult.Match<Response<Order>>(
     onSuccess:(order) => new Response<Order>() { Data = order },
     onFailure:(errors) => new Response<Order>() { Error = new { Error = errors.ToList() } });

//gets first error of the list as the arg when failure.
 Response<Order> response = orderCreateResult.MatchFirst<Response<Order>>(
     onSuccess:(order) => new Response<Order>() { Data = order },
     onFailure:(error) => new Response<Order>() { Error = new { Error = errors.ToList() } });


 Response<Order> response = orderCreateResult.MatchAsync<Response<Order>>(
     onSuccess: async (order) => {},
     onFailure: async (errors) => {});

//gets first error of the list as the arg when failure.
 Response<Order> response = orderCreateResult.MatchFirstAsync<Response<Order>>(
     onSuccess: async (order) => {},
     onFailure: async (error) => {});