FluentResult

This is a lightweight .NET library, that can be used for returning and validating Result without relaying on exceptions.

You can install ResultFluent with NuGet:

dotnet add package ResultFluent

Models

class Result<TModel> { TModel Data { get; } ResultComplete Status { get; } ICollection<string> Messages { get; } bool IsSuccessfulStatus(); } class ResultOfItems<TItem> : Result<IEnumerable<TItem>> { ResultMetadata Metadata { get; } }

Creating a Result

A Result can store Data, Messages and Status code.

Model model = new Model(); // create a result which indicates success Result<Model> successResult = new Result<Model>(model, ResultComplete.Success, messages); // or Result<Model> successResult = new Result<Model>(model); // Status = Success, Messages = null // or just Result<Model> successResult = Result.Create(model); // We can also add success messages Result<Model> successResult = Result.Create(model, "OK"); // create a result which indicates error Result<Model> errorResult = new Result<Model>(model, ResultComplete.InvalidArgument, new [] { "Model identifier must be a positive number" }); // or Result<Model> errorResult = Result.CreateResultWithError<Model>(ResultComplete.NotFound, "Model not found");

Map and MapAsync

// simple map Result<string> result = Result .Create(5) .Map(value => value * 2) .Map(value => $"value is {value}"); // result.Data == "value is 10" // async map Result<UserModel> result = await Result .Create(requestedUserId) .MapAsync(async userId => await _userRepository.GetByIdAsync(userId)) .MapAsync(user => ConvertUserToUserModel(user));

Validating

Static validation

int userId = -1; string userName = string.Empty; Result<bool> validateResult = Result .Validate(userId > 0, ResultComplete.InvalidArgument, "User identifier must be positive number") .Validate(userName.Length > 0, ResultComplete.InvalidArgument, "User name is required"); // validateResult: // Data = false // Status = InvalidArgument // Messages = string[] { "User identifier must be positive number", "User name is required" } string userName = "someLongUserName"; Result<bool> validateResult = Result .Create(userName) .Validate( x => x.Length < 5, ResultComplete.InvalidArgument, x => $"User name must be less than 5 symbols, the provided value was {x.Length} symbols.") // validateResult: // Data = "someLongUserName" // Status = InvalidArgument // Messages = string[] { "User name must be less than 5 symbols, the provided value was 12 symbols." }

Validate can skip rules on fail

Result<bool> validateResult = Result .Create(userModel) .Validate(user => user != null, ResultComplete.InvalidArgument, "User model is null") .Validate(user => user.UserId > 0, ResultComplete.InvalidArgument, "User identifier is required", skipOnInvalidResult: true);

Validate nullable

Result<bool> validateResult = Result .Create<string?>(name) .ValidateNotNull(ResultComplete.InvalidArgument, "Name is null") .Validate(name => /** name is not null */, ResultComplete.InvalidArgument, "");

Chain validation and mapping

Task<Result<User>> UpdateUserAsync(int userId, string userName) { var userUpdateResult = Result .Validate( userId > 0, ResultComplete.InvalidArgument, "User identifier must be positive number") .Validate( userName.Length > 0, ResultComplete.InvalidArgument, "User name is required") .MapAsync( isValid => _userRepository.GetByIdAsync(userId)) .ValidateAsync( user => user != null, ResultComplete.NotFound, "User doesn't exists") .MapAsync( async user => { user.UserName = userName; var updatedUser = await _userRepository.UpdateUserAsync(user); return updatedUser; }) .ValidateAsync( updatedUser => updatedUser != null, ResultComplete.OperationFailed, "User was not updated"); return userUpdateResult; } await UpdateUserAsync(10, ""); // Status=InvalidArgument, Messages=["User name is required"], Data=null await UpdateUserAsync(100, "Rosen"); // One of the following: // // Status=NotFound, Messages=["User doesn't exists"], Data=null // Status=OperationFailed, Messages=["User was not updated"], Data=null // Status=Success, Messages=null, Data={ UserId=100, UserName="Rosen" }

Switch Mapping

You may need to use multiple method returning Result. For that reason there is Switch method.

Result<int> Multiply(int a, int b) => Result.Create(a + b); Result<int> AddAndDouble(int a, int b) => Result .Create(a + b) .Switch(value => Multiply(value, 2)) .Map(value => $"The result is {value}"); AddAndDouble(2, 3) // Data = "The result is 10"

Ensure successful result and return data

// return user or throw exception User validatedUser = Result .Create(user) .ValidateNotNull(ResultComplete.InvalidArgument, string.Empty) .AsValidData(); // When invalid we throw [ResultValidationException](src/FluentResult/ResultValidationException.cs). Result .Validate(false, ResultComplete.OperationFailed, "Invalid result") .AsValidData(); // We can also use `AsValidDataAsync` for `Task<Result<TSource>>` and `Task<ResultOfItems<TSource>>`. Result.Create(5) .MapAsync(Task.FromResult) .AsValidDataAsync();

Catch Exception

We can catch async exception by using the Catch extensions.

Result<User> result = Result .Create(requestedUserId) .MapAsync(userId => getUserAsync(userId)) .CatchAsync(ex => Result.CreateResultWithError<User>(ResultComplete.OperationFailed, ex.Message));

ResultOfItems

The result of items is a result that contain metadata for a collection of items.

ResultOfItems<int> result = new ResultOfItems<int>( items: new [] { 4, 5 }, status: ResultComplete.Success, messages: null, totalCount: 5, pageSize: 3, pageIndex: 1, count: 2 ); // is the same as ResultOfItems<int> result = Result.CreateResultOfItems( items: new [] { 4, 5 }, totalCount: 5, pageSize: 3, pageIndex: 1); // or may be ResultOfItems<Item> GetItemsByPage(int pageIndex, int pageSize) => Result .Validate(pageIndex >= 0, ResultComplete.InvalidArgument, "Page index is invalid") .Validate(pageSize > 0, ResultComplete.InvalidArgument, "Page size is invalid") .MapAsync( isValid => _itemsRepository.GetByPageAsync(pageIndex, pageSize)) .ToResultOfItemsAsync( data => Result.CreateResultOfItems(data.Items, data.TotalCount, pageSize, pageIndex)); // or simply ResultOfItems<Item> GetItemsByPage(int pageIndex, int pageSize) => Result .Validate(pageIndex >= 0, ResultComplete.InvalidArgument, "Page index is invalid") .Validate(pageSize > 0, ResultComplete.InvalidArgument, "Page size is invalid") .MapAsync(_ => _itemsRepository.GetByPageAsync(pageIndex, pageSize)) .ToResultOfItemsAsync();

Combine and CombineAsync

// We can combine from 1 to 5 results. var helloWorld = Result.Create("Hello").Combine( number => Result.Create("World"), (a, b) => a + b); // Sum is 9 var sum = Result.Create(2).Combine( number => ( Result.Create(3), Result.Create(4)), (a, b, c) => a + b + c); // async example Task<Result<Classroom>> UpdateClassroomAsync(UpdateClassroomRequest request) => Result .Validate(request != null, ResultComplete.InvalidArgument, "The request must not be null") .MapAsync(_ => _classroomRepository.GetByIdAsync(request.Id)) .CombineAsync( classroom => ( _schoolRepository.GetByIdAsync(request.SchoolId), _userRepository.GetByIdAsync(request.TeacherId)), async (classroom, school, teacher) => { classroom.School = school; classroom.Teacher = teacher; await _classroomRepository.UpdateAsync(classroom); });

Async helper class

The Async is a helper structure to reduce code definitions.

Task<Result<IReadOnlyList<string>>> GetNamesAsync(); // Becomes Async<IReadOnlyList<string>> GetNamesAsync();

We can use .AsAsync() extension method.

Async task = Result.Create(5).MapAsync(Task.FromResult).ToAsync();

Deserialize the as Result

In order to deserialize it we need to add JsonConstructorAttribute, because all properties are with private set. For this to happen we need to use System.Test.Json or Newtonsoft.Json. This library do not include it, because we do not want to depend on specific serialization. It can be achieved by inhering the class like:

// my /Result{TResult}.cs using Newtonsoft.Json; // ... public class Result<TResult> : FluentResult.Result<TResult> { [JsonConstructor] public Result(TResult data, FluentResult.ResultComplete status, ICollection<string> messages) : base(data, status, messages) { } }

or

using System.Text.Json.Serialization; // ... public class Result<TResult> : FluentResult.Result<TResult> { [JsonConstructor] public Result(TResult data, FluentResult.ResultComplete status, ICollection<string> messages) : base(data, status, messages) { } }