How can we return multiple error messages with Result class?

[nagtilaklaxman]

Want to return multiple error messages with result class . Is it possible ?

[vkhorikov]

Sorry for late reply. If it's a string Result, then you should be able to do this via putting multiple strings to its Error field. If it's a strongly-typed error (custom Error class), then you'd need to come up with your own ErrorList and use it as Result<T, ErrorList>.

You can open an issue with this feature request. There was a discussion of this issue some time ago, but I don't think we have a dedicated ticket to track the progress.

[redx177]

We have this implemented like this:

public class ErrorList : CombinableList<IError>
{
    public ErrorList() : base() {}
    public ErrorList(IError error) : base(error) {}
    public ErrorList(IEnumerable<IError> errors) : base(errors) {}

    public override string ToString() {
        return string.Join(", ", this.Select(error => $"[{error.ErrorCode}] {error.ErrorDescription}"));
    }
}

public class CombinableList<T> : ICombine, IList<T>
{
    public ICombine Combine(ICombine item)
    {
        _items.AddRange(((CombinableList<T>)item)._items);
        return this;
    }

   [ leaving out a whole lot of code required to implement an IList for brevity ]
}

public interface IError
{
    string ErrorCode { get; }
    string ErrorDescription { get; }
}

You can put in IError what ever you need/want. We use then specific IError implementations to create errors.

E.g.

public class MyError : IError
{
    public string ErrorCode { get; init; } = "0001";
    public string ErrorDescription { get; init; }

    public MyError (string name)
    {
        ErrorDescription = $"Error for {name}";
    }
}

Additionally for ease of use, we have an extension method on IError to convert it to an ErrorList:

public static class IErrorExtensions
{
    public static ErrorList ToList(this IError error)
    {
        return new ErrorList(error);
    }
}

Then you can use Result<T, ErrorList> like this:

var a1 = Result.SuccessIf(
    isSuccess: 1 == 2,
    value: new Something(),
    error: new MyError("abc").ToList());

var a2 = Result.SuccessIf(
    isSuccess: 1 == 3,
    value: new Something(),
    error: new MyError("def").ToList());

var a3 = Result.Combine<ErrorList>(a1, a2);