CSharpEssentials.Errors 6.5.2

CSharpEssentials.Errors

Structured, type-safe error handling for .NET. Errors are data, not exceptions.

Features

• Error Struct: Value-type error with code, description, type, and metadata.
• Standard Error Types: Failure, Validation, NotFound, Conflict, Unauthorized, Forbidden, Unexpected. ErrorType also has an Unknown member, which has no factory method.
• ErrorMetadata: Attach contextual data to errors fluently.
• Exception Bridge: Convert exceptions to Error or throw DomainException / EnhancedValidationException.
• HTTP Mapping: Built-in conversion between ErrorType and HTTP status codes.

Targets net11.0, net10.0, net9.0 and netstandard2.1. Depends on CSharpEssentials.Core and CSharpEssentials.Enums.

Installation

dotnet add package CSharpEssentials.Errors

Usage

Creating Errors

using CSharpEssentials.Errors;

Error notFound = Error.NotFound("User.NotFound", "User was not found.");
Error validation = Error.Validation("Email.Invalid", "Email format is invalid.");
Error conflict = Error.Conflict("User.Duplicate", "User already exists.");
Error failure = Error.Failure("Payment.Failed", "Payment was rejected.");
Error forbidden = Error.Forbidden("Order.Forbidden", "You cannot cancel this order.");
Error unauthorized = Error.Unauthorized("Token.Expired", "The token has expired.");
Error unexpected = Error.Unexpected("Db.Down", "The database is unreachable.");

Every factory takes code, description and an optional ErrorMetadata, and all three have defaults: Error.NotFound() has the code NotFound and the description A 'Not Found' error has occurred. An Error exposes Code, Description, Type, NumericType (the int value of Type) and Metadata (null when none was given). It implements IError, and two errors are equal when type, code, description and metadata entries are equal.

Error Metadata

Error withMeta = Error.NotFound(
    "User.NotFound",
    "User was not found.",
    new ErrorMetadata()
        .AddMetadata("TraceId", Guid.NewGuid().ToString())
        .AddMetadata("RequestPath", "/api/users/123"));

ErrorMetadata is a Dictionary<string, object?>. AddMetadata keeps the existing value when the key is already present. AddStackTrace, AddException and AddExceptionDetailed add well-known keys (stackTrace, exception, exceptionType, exceptionStackTrace, exceptionMessage, innerException), Combine merges another instance without overwriting, and CreateEmpty, CreateWithStackTrace, CreateWithException and CreateWithExceptionDetailed are the static counterparts.

Combining Errors

Error a = Error.Validation("Name.Empty", "Name is required.");
Error b = Error.Validation("Email.Invalid", "Email is invalid.");

Error[] combined = a + b;

Error[] many = Error.CreateMany(a, b);                          // params of Error or of Error collections
Error[] single = a;                                             // implicit Error -> Error[]

Converting from Exceptions

try { /* ... */ }
catch (Exception ex)
{
    Error error = Error.Exception(ex);
}

Error.Exception(ex) uses the exception type name as the code, the exception message as the description and ErrorType.Failure. The metadata carries exceptionType, exceptionStackTrace, exceptionMessage and, when there is one, a nested innerException. Overloads take an explicit code, an explicit code and description, an ErrorType and extra ErrorMetadata:

Error custom = Error.Exception("Orders.SaveFailed", "The order could not be saved.", ex, ErrorType.Unexpected);

Domain Exceptions

using CSharpEssentials.Errors;
using CSharpEssentials.Exceptions;

Error error = Error.Validation("Order.Invalid", "Total must be greater than zero.");
throw new DomainException(error);

DomainException and EnhancedValidationException live in the CSharpEssentials.Exceptions namespace of this package; see the exception types.

HTTP Status Mapping

int status = ErrorType.NotFound.ToHttpStatusCode();     // 404
ErrorType type = 401.ToErrorType();                      // Unauthorized

ToErrorType is the reverse for 400, 401, 403, 404, 409 and 500 (Failure); every other status code gives Unexpected.

Domain-Specific Error Hierarchies

Error is a value type (readonly record struct) and cannot be subclassed. The idiomatic way to build domain-specific, typed error hierarchies is to group static factory methods in a dedicated class per aggregate or bounded context:

using CSharpEssentials.Errors;

// Organize errors by domain aggregate
public static class UserErrors
{
    public static Error NotFound(Guid id) =>
        Error.NotFound("User.NotFound", $"User '{id}' was not found.");

    public static readonly Error AlreadyExists =
        Error.Conflict("User.AlreadyExists", "A user with that email already exists.");

    public static Error InvalidAge(int age) =>
        Error.Validation("User.InvalidAge", $"Age {age} is not allowed; must be 18 or older.");

    public static readonly Error Unauthorized =
        Error.Unauthorized("User.Unauthorized", "You are not authorized to perform this action.");
}

public static class OrderErrors
{
    public static readonly Error EmptyCart =
        Error.Validation("Order.EmptyCart", "Cannot place an order with an empty cart.");

    public static Error InsufficientFunds(decimal required, decimal available) =>
        Error.Failure(
            "Order.InsufficientFunds",
            $"Payment requires {required:C} but only {available:C} is available.",
            new ErrorMetadata().AddMetadata("Required", required).AddMetadata("Available", available));
}

Usage with Result:

using CSharpEssentials.ResultPattern; // CSharpEssentials.Results package

public Result<User> FindUser(Guid id)
{
    User? user = _repo.Find(id);
    if (user is null)
        return UserErrors.NotFound(id);   // implicit Error → Result<User>

    return user;
}

public Result PlaceOrder(Cart cart, decimal balance)
{
    if (cart.IsEmpty)
        return OrderErrors.EmptyCart;

    if (balance < cart.Total)
        return OrderErrors.InsufficientFunds(cart.Total, balance);

    return Result.Success();
}

This pattern provides discoverability (IDE autocomplete per domain), type-safe error codes, and centralised descriptions, all without inheritance.