Asp.net core web api

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Controller

Controllers/ItemsController.cs
[ApiController]
[Produces("application/json")]  // force le format JSON
[ApiVersion("1")]  // need nuget package Microsoft.AspNetCore.Mvc.Versioning
[Route("api/[controller]")]     // /api/items
public class ItemsController : ControllerBase
{
    private readonly IItemsRepository itemsRepository;
    private readonly IMapper mapper;

    public ItemsController(IItemsRepository itemsRepository, IMapper mapper)
    {
        this.itemsRepository = itemsRepository;
        this.mapper = mapper;

GET

Csharp.svg
[HttpGet]
[ProducesResponseType(typeof(IReadOnlyList<ItemDto>), StatusCodes.Status200OK)]
public async Task<IActionResult> GetAllAsync()
{
    var items = await itemsRepository.GetAllAsync()
    var itemDtos = mapper.Map<IReadOnlyList<ItemDto>>(items);
    return Ok(itemDtos);
}

[HttpGet("{id:int}")]
[ProducesResponseType(typeof(ItemDto), StatusCodes.Status200OK)]
[ProducesResponseType(StatusCodes.Status400BadRequest)]
[ProducesResponseType(StatusCodes.Status404NotFound)]
[ProducesResponseType(StatusCodes.Status500InternalServerError)]
public async Task<IActionResult> GetByIdAsync(int id)
{
    try
    {
        if (id <= 0)
        {
            return BadRequest();
        }

        var item = await itemsRepository.GetByIdAsync(id)
        if (item == null)
        {
            return NotFound();
        }

        var itemDto = mapper.Map<ItemDto>(item);
        return Ok(itemDto);
    }
    catch (Exception ex)
    {
        // using Microsoft.AspNetCore.Http;
        return StatusCode(StatusCodes.Status500InternalServerError, $"Failed to get Item {id} ({ex})");
    }
}


[HttpGet]
[ProducesResponseType(typeof(IReadOnlyList<ItemDto>), StatusCodes.Status200OK)]
public async Task<IActionResult> GetAsync([FromQuery] ItemQueryDto itemQueryDto)
{
    var itemQuery = this.mapper.Map<ItemQuery>(itemQueryDto);
    var items = await itemsRepository.GetAsync(itemQuery);
    var itemDtos = this.mapper.Map<IReadOnlyList<ItemDto>>(items);
    return Ok(itemDtos);
}

POST

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[HttpPost]
[ProducesResponseType(typeof(ItemDto), StatusCodes.Status201Created)]
public async Task<IActionResult> CreateAsync(ItemDto itemDto)
{
    var item = this.mapper.Map<Item>(itemDto);
    var createdItem = await itemsRepository.AddAsync(item);
    var createdItemDto = this.mapper.Map<ItemDto>(createdItem);
    return Created(HttpContext.Request.Path, createdItemDto);

    return Created($"https://localhost:5001/api/items/{createdItem.Id}", createdItemDto);
    return CreatedAtAction(nameof(Get), new { id = createdItem.Id }, createdItemDto);
    return CreatedAtRoute("api", new { 
        controller =  "items", 
        action = nameof(Get), 
        id = $"{createdItem.Id}" 
    }, createdItemDto);
}
Startup.cs
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseMvc(routes => {
        routes.MapRoute(
            name: "api",
            template: "api/{controller=Items}/{id?}");
    });

PUT / Update

Csharp.svg
[ProducesResponseType(StatusCodes.Status204NoContent)]
[ProducesResponseType(StatusCodes.Status400BadRequest)]
[ProducesResponseType(StatusCodes.Status404NotFound)]
public async Task<IActionResult> UpdateAsync(int id, ItemDto itemDto)
{
    if (id <= 0)
    {
        return BadRequest();
    }

    var itemToUpdate = await itemsRepository.GetByIdAsync(id);
    if (itemToUpdate == null)
    {
        return NotFound();
    }

    var item = this.mapper.Map<Item>(itemDto);
    await itemsRepository.UpdateAsync(itemToUpdate, item);

    return NoContent();
}

DELETE

Csharp.svg
[HttpDelete("{id:int}")]
[ProducesResponseType(StatusCodes.Status204NoContent)]
[ProducesResponseType(StatusCodes.Status400BadRequest)]
[ProducesResponseType(StatusCodes.Status404NotFound)]
public async Task<IActionResult> DeleteAsync(int id)
{
    if (id <= 0)
    {
        // do not provide details
        return BadRequest();
        // return a string instead of ProblemDetails
        return BadRequest("id must be greater than 0.");
        // same as BadRequest() but with detail
        return Problem(
            title: "Bad Request",
            detail: "id must be greater than 0.",
            statusCode: StatusCodes.Status400BadRequest);
    }

    var itemToDelete = await itemsRepository.GetByIdAsync(id);
    if (itemToDelete == null)
        return NotFound();

    await itemsRepository.DeleteAsync(id);
    return NoContent();
}

Client

Client/ItemClient.cs
public class ItemClient : IItemClient
{
    private const string Path = "item";
    private const string ApiVersion = "1";

    private readonly HttpClient httpClient;
    private readonly QueryBuilder queryBuilder;

    // injection de HttpClient
    public ItemDataService(HttpClient httpClient)
    {
        this.httpClient = httpClient;

        queryBuilder = new QueryBuilder();
        queryBuilder.Add("api-version", ApiVersion);
    }

GET

ReadAsAsync

Csharp.svg
public async Task<IReadOnlyList<ItemDto>> GetAllItemsAsync(CancellationToken cancellationToken)
{
    var uri = new Uri($"{Path}{queryBuilder.ToQueryString()}", UriKind.Relative);

    var response = await this.httpClient.GetAsync(uri, cancellationToken);
    response.EnsureSuccessStatusCode();

    var items = await response.Content.ReadAsAsync<IReadOnlyList<ItemDto>>(cancellationToken);
    return items;
}
Bash.svg
dotnet add package Microsoft.AspNet.WebApi.Client

JsonSerializer.DeserializeAsync

Csharp.svg
public async Task<IReadOnlyList<ItemDto>> GetAllItemsAsync()
{
    return await JsonSerializer.DeserializeAsync<IEnumerable<Item>>(
        await _httpClient.GetStreamAsync("api/item"),
        new JsonSerializerOptions()
        {
            PropertyNameCaseInsensitive = true
        });

    var response = await _httpClient.GetAsync("api/item");
    if (!response.IsSuccessStatusCode)
        throw new HttpRequestException(response.ReasonPhrase);
        
    return await JsonSerializer.DeserializeAsync<IEnumerable<Item>>(
        await response.Content.ReadAsStreamAsync(),
        new JsonSerializerOptions()
        {
            PropertyNameCaseInsensitive = true
        });
}

public async Task<Item> GetItemAsync(int itemId)
{
    return await JsonSerializer.DeserializeAsync<Item>(
        await _httpClient.GetStreamAsync($"api/item/{itemId}"),
        new JsonSerializerOptions()
        {
            PropertyNameCaseInsensitive = true
        });

    var response = await _httpClient.GetAsync($"item/{itemId}");
    if (!response.IsSuccessStatusCode)
        throw new HttpRequestException(response.ReasonPhrase);
        
    return await JsonSerializer.DeserializeAsync<Item>(
        await response.Content.ReadAsStreamAsync());    
}

POST

Csharp.svg
public async Task<Item> AddItemAsync(Item item)
{
    var itemJson =
        new StringContent(JsonSerializer.Serialize(item), Encoding.UTF8, "application/json");

    var response = await _httpClient.PostAsync("api/item", itemJson);

    if (response.IsSuccessStatusCode)
    {
        return await JsonSerializer.DeserializeAsync<Item>(await response.Content.ReadAsStreamAsync());
    }

    return null;
}

PUT

Csharp.svg
public async Task UpdateItemAsync(Item item)
{
    var itemJson = new StringContent(JsonSerializer.Serialize(item), Encoding.UTF8, "application/json");

    var response = await _httpClient.PutAsync("api/item", itemJson);
    if (!response.IsSuccessStatusCode)
    {
        var validationProblem = await JsonSerializer.DeserializeAsync<ValidationProblemDetails>(
            await response.Content.ReadAsStreamAsync());
        // validationProblem.Errors: key = property, values = error list
    }
}

DELETE

Csharp.svg
public async Task DeleteItemAsync(int itemId)
{
    var response = await _httpClient.DeleteAsync($"api/item/{itemId}");
    if (!response.IsSuccessStatusCode)
    {
        var validationProblem = await JsonSerializer.DeserializeAsync<ValidationProblemDetails>(
            await response.Content.ReadAsStreamAsync());
        throw new HttpRequestException($"{validationProblem.Title}: {validationProblem.Detail}");
    }
}

API versioning

Need nuget package Microsoft.AspNetCore.Mvc.Versioning
Controllers/ItemsController.cs
[ApiVersion("1")]
[ApiController]
public class ItemsController : ControllerBase
Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers();
    services.AddApiVersioning();
Url: /api/items?api-version=1

Health check

Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddHealthChecks();
    // ...

public void Configure(IApplicationBuilder app)
{
    app.UseEndpoints(endpoints =>
    {
        endpoints.MapHealthChecks("/health");
    });
    // ...

Validation

ItemViewModel.cs
public class ItemViewModel
{
    public int Id { get; set; }
    [Required]
    [MinLength(6)]
    public string Name { get; set; }
}
Csharp.svg
[HttpPost]
public IActionResult Post([FromBody]ItemViewModel itemVm)
{
    // ce code n'est plus nécessaire car pris en charge par les automatic HTTP 400 responses
    if (!ModelState.IsValid)
    {
        return BadRequest(ModelState);
    }

    var item = itemVm.ToEfItem();
    _repository.Add(item);
    if (_repository.SaveAll())
    {
        var newItemVm = new ItemViewModel(item);
        return Created($"/api/ListApi/{newItemVm.Id}", newItemVm);
    }
    else
    {
        return BadRequest("Failed to save.");
    }

Automatic HTTP 400 responses

L'attribut [ApiController] effectue automatiquement une validation du modèle et envoie une réponse HTTP 400 en cas d'erreur.
Il n'est donc plus nécessaire de tester ModelState.IsValid.
ASP.NET Core MVC utilise le filtre d'action ModelStateInvalidFilter pour tester la validité du modèle.
Exemple de réponse en cas d'erreur de validation du modèle:

Json.svg
{
    "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
    "title": "One or more validation errors occurred.",
    "status": 400,
    "traceId": "|b659be6b-4fc34f5e9f3caf17.",
    "errors": {
        "Name": [
            "The Name field is required."
        ]
    }
}
Csharp.svg
// déserialiser la réponse
var content = await response.Content.ReadAsStreamAsync();
var validationProblem = await JsonSerializer.DeserializeAsync<ValidationProblemDetails>(content);

Fluent Validation

Bash.svg
dotnet add package FluentValidation.AspNetCore
Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers()
            .AddFluentValidation();

    services.AddTransient<IValidator<ItemDto>, ItemValidator>();
Validation/ItemValidator.cs
public class ItemValidator : AbstractValidator<ItemDto>
{
    public ItemValidator()
    {
        RuleFor(x => x.Name).NotEmpty();

Query Strings

Url: http://localhost:80/api/items?option1=true

ItemsController.cs
[HttpGet]
public IActionResult Get(bool option1 = false)  // par défaut à false
{ }

Dependency Injection

Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers();

    services.AddTransient<IMyService, MyService>();

Images

Download

MyController.cs
[HttpGet]
public IActionResult Get()
{
    var filePath = Path.Combine("~", "folder", "image.jpeg");
    // VirtualFileResult
    return File(filePath, "image/jpeg");
}

Base64

MyController.cs
[HttpGet]
public IActionResult Get()
{
    var filePath = Path.Combine("~", "folder", "image.jpeg");
    byte[] bytesArray = System.IO.File.ReadAllBytes(filePath);
    return Ok("data:image/jpeg;base64," + Convert.ToBase64String(bytesArray));
}

Upload

MyController.cs
[HttpPost]
public async Task<IActionResult> Post([FromForm]IFormFile myFile)
{
    var filePath = Path.Combine(folderPath, photo.FileName);
    using (var stream = new FileStream(filePath, FileMode.Create))
    {
        await myFile.CopyToAsync(stream);
    }

    return Ok(filePath);
}

Postman → Body → form-data

  • key: myFile
  • File
  • Value: Choose Files
Si myFile est toujours null, enlever [FromForm]

Renvoyer le message d'erreur des exceptions

Exception handler

Startup.cs
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        //app.UseDeveloperExceptionPage();
        app.UseExceptionHandler("/error-local-development");
    }
    else
    {
        app.UseExceptionHandler("/error");
    }
Controllers/ErrorController.cs
[ApiController]
public class ErrorController : ControllerBase
{
    [Route("/error-local-development")]
    public IActionResult ErrorLocalDevelopment([FromServices] IWebHostEnvironment webHostEnvironment)
    {
        if (webHostEnvironment.EnvironmentName != "Development")
        {
            throw new InvalidOperationException("This shouldn't be invoked in non-development environments.");
        }

        var context = HttpContext.Features.Get<IExceptionHandlerFeature>();

        return Problem(
            title: $"{context.Error.GetType().Name}: {context.Error.Message}",
            detail: context.Error.StackTrace);
    }

    [Route("/error")]
    public IActionResult Error() => Problem();  // "title": "An error occured while processing your request."
    public IActionResult Error()
    {
        var context = HttpContext.Features.Get<IExceptionHandlerFeature>();
        return Problem(detail: $"{context.Error.GetType().Name}: {context.Error.Message}");
    }
}

ExceptionFilterAttribute

ApiExceptionFilterAttribute.cs
public class ApiExceptionFilterAttribute : ExceptionFilterAttribute
{
    public override void OnException(ExceptionContext context)
    {
        context.HttpContext.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
        context.HttpContext.Response.ContentType = "text/plain";
        context.HttpContext.Response.WriteAsync(context.Exception.Message).ConfigureAwait(false);
    }
}
MyController.cs
[ApiExceptionFilter]
[Route("api/[controller]")]
public class MyController : Controller

ExceptionMiddleware

ExceptionMiddleware.cs
public class ExceptionMiddleware
{
    public async Task Invoke(HttpContext context)
    {
        context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;

        var ex = context.Features.Get<IExceptionHandlerFeature>()?.Error;
        if (ex == null) return;

        context.Response.ContentType = "text/plain";
        await context.Response.WriteAsync(ex.Message);
    }
}
Startup.cs
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseExceptionHandler(new ExceptionHandlerOptions 
    {
        ExceptionHandler = new ExceptionMiddleware().Invoke
    });

    app.UseMvc();

Différencier la gestion d'erreur pour mvc et webapi

Utiliser un ApiExceptionFilterAttribute et un MvcExceptionFilter

UseWhen et UseExceptionHandler

Startup.cs
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseWhen(x => x.Request.Path.Value.StartsWith("/api"), builder =>
    {
        builder.UseExceptionHandler(new ExceptionHandlerOptions 
        {
            ExceptionHandler = new ExceptionMiddleware().Invoke
        });
    });
    app.UseWhen(x => !x.Request.Path.Value.StartsWith("/api"), builder =>
    {
        builder.UseExceptionHandler("/Home/Error");
    });

UseExceptionHandler

ExceptionMiddleware.cs
public class ExceptionMiddleware
{
    public async Task Invoke(HttpContext context)
    {
        if (context.Request.Path.Value.StartsWith("/api"))
        {
            context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;

            var ex = context.Features.Get<IExceptionHandlerFeature>()?.Error;
            if (ex == null) return;

            context.Response.ContentType = "text/plain";
            await context.Response.WriteAsync(ex.Message).ConfigureAwait(false);
        }
        else
        {
            // redirect to /Home/Error
        }
    }
}

UseStatusCodePagesWithReExecute

Startup.cs
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseStatusCodePagesWithReExecute("/error/{0}");
    app.UseExceptionHandler("/error/500");

    app.UseMvc();
Csharp.svg
[HttpGet("/error/{code:int}")]
public string Error(int code)
{
    return $"Error: {code}";
}

JSON serialization: Newtonsoft.Json vs System.Text.Json

By default .NET Core 3.0 uses System.Text.Json.

Use Newtonsoft.Json

Bash.svg
dotnet add package Microsoft.AspNetCore.Mvc.NewtonsoftJson
Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers();
            .AddNewtonsoftJson();

Erreurs

Unsupported Media Type with Postman

  • Body → raw = json à envoyer
  • Headers → Content-Type = application/json

JsonSerializationException: Self referencing loop detected for property 'xxx' ...

Startup.cs
services.AddMvc()
    // ignorer les références circulaires entre objets dans EF pour JSON
    .AddJsonOptions(opt => opt.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore);

SqlException: Cannot insert explicit value for identity column in table 'xxx' when IDENTITY_INSERT is set to OFF

Impossible de sauvegarder les changements si une entité a été insérée avec une valeur ≠ default dans une propriété bindée avec une colonne Identity.
Solution: forcer la valeur de cette propriété a default. La bdd mettra la valeur de la propriété a jour après avoir inséré l'entité.