I have a simple web-app with angular on client-side and asp.net core web-api on server-side. I use InMemoryDatabase
services.AddDbContext<ItemsContext>(options => options.UseInMemoryDatabase("ItemsDB"));
to store data for the simplisity of the development. But I've encountered an issue with that. I have one controller on web-api to response for users' requests:
[Route("api/[controller]")]
public class ItemsController : Controller
{
private readonly IApiService apiService;
public ItemsController(IApiService apiService)//using DI from Startup.cs
{
this.apiService = apiService;
}
[HttpPost, Route("addItem")]
public async Task<Response> Add([FromBody]Item item)
{
return await apiService.Add(item);
}
[HttpDelete("{id}")]
public async Task<Response> Delete(int id)
{
return await apiService.Delete(id);
}
[HttpPut]
public async Task<Response> Put([FromBody]Item item)
{
return await apiService.Put(item);
}
}
and the following Startup.cs configurations:
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc();
services.AddDbContext<ItemsContext>(options => options.UseInMemoryDatabase("ItemsDB"));
services.AddSingleton<IUnitOfWork, UnitOfWork>(provider => {
var context = services.BuildServiceProvider().GetService<ItemsContext>();
return new UnitOfWork(context);
});
services.AddSingleton<IApiService, ApiService>(provider => {
return new ApiService(services);
});
}
The problem is, that when I add new item, everything goes just fine...but then I post another request to delete this item it may show there there is no such an item at all or sometimes it may delete it...so in other words, the database exists and then disappears and I'm not sure when. Here is some additional code refering to the above
public class ApiService: IApiService
{
private readonly IUnitOfWork database;
private readonly IServiceProvider provider;
public ApiService(IServiceCollection serviceCollection)
{
provider = serviceCollection.BuildServiceProvider();
}
public IUnitOfWork Database
{
get
{
return provider.GetService<IUnitOfWork>();
}
}
public async Task<Response> Add(Item item)
{
Database.Items.Add(item);
await Database.SaveAsync();
var id = Database.Items.LastItem().Id;
return new Response() { Result = true, ItemId = id };
}
public async Task<Response> Delete(int id)
{
var item = await db.Items.Find(id);
Database.Items.Remove(item);
await Database.SaveAsync();
return new Response() { Result = true };
}
public async Task<Response> Put(Item item)
{
Database.Items.Update(item);
await Database.SaveAsync();
return new Response() { Result = true };
}
}
Update:
UnitOfWork Implementation:
public class UnitOfWork: IUnitOfWork
{
private readonly DbContext context;
private IRepository<Item> itemsRepository;
public UnitOfWork(DbContext dbContext)
{
context = dbContext;
}
public IRepository<Item> Items
{
get
{
return itemsRepository ?? (itemsRepository = new Repository<Item>(context));
}
}
public void Dispose()
{
context.Dispose();
}
public void Save()
{
context.SaveChanges();
}
public async Task SaveAsync()
{
await context.SaveChangesAsync();
}
}
Your code has multiple serious problems, let's go through them.
services.AddDbContext adds a Scoped service, meaning that instances will be created and disposed on each request. services.AddSingleton adds a Singleton service, so only a single instance will ever be created. You cannot add a scoped service to a singleton one, because the reference the singleton service uses will be disposed and you will end up with a disposed context.
This code:
return provider.GetService<IUnitOfWork>();
represents the service locator anti-pattern. As you can guess, an anti-pattern is something you want to avoid. I also don't know why you would want a service to build the entire DI container nor why you would want a service to have the responsibility of getting the dependencies it needs itself.
This part here is where your question actually comes from:
Database.SaveAsync();
You are calling an asynchronous function and not awaiting for it to finish. The task may finish or not, it may throw an error or not, you will never know what happened.
The best thing is that all of these could be avoided if people stopped attempting to create a Unit of Work + Repository pattern over yet another Unit of Work and Repository. Entity Framework Core already implements these:
DbContext => Unit of Work
DbSet => Repository (generic)
Why do you want yet another abstraction? Will you really ever throw away EF Core from the project to justify the maintenance cost of your code?
The entire question code could have just been this:
[Route("api/[controller]")]
public class ItemsController : Controller
{
private readonly YourContext _context;
public ItemsController(YourContext context)
{
_context = context;
}
[HttpPost]
public async Task<IActionResult> Add([FromBody]Item item)
{
context.Items.Add(item);
await context.SaveChangesAsync();
return Ok(item.Id);
}
[HttpDelete("{id}")]
public async Task<IActionResult> Delete(int id)
{
var item = await context.Items.FindAsync(id);
context.Items.Remove(item);
await context.SaveChangesAsync();
return Ok();
}
[HttpPut]
public async Task<IActionResult> Put([FromBody]Item item)
{
context.Items.Update(item);
await context.SaveChangesAsync();
return Ok();
}
}
Related
I'm having trouble with a Scoped context getting disposed before a controller route has finished executing...
This is example code that demonstrates the problem as I can't share the real code
I have a Unit of Work that would 'wrap' the repository layer
public interface IUnitOfWork
{
void Dispose();
bool GetContextDisposed();
}
public class UnitOfWork : IDisposable, IUnitOfWork
{
private ISomeContext _context;
public ISomeRepository someRepository;
public UnitOfWork(ISomeContext context)
{
_context = context;
someRepository = new SomeRepository(_context);
}
public void Dispose()
{
_context.Dispose();
}
public bool GetContextDisposed()
{
return _context.GetDisposed();
}
}
Context
public interface ISomeContext
{
void Dispose();
public bool GetDisposed();
}
public class SomeContext : IDisposable, ISomeContext
{
private bool isDisposed = false;
public void Dispose()
{
Console.WriteLine("Dispose being called on Context");
isDisposed = true;
}
public bool GetDisposed()
{
return isDisposed;
}
}
These are both registered as scoped as I want to get one per request to an endpoint
services.AddScoped<ISomeContext, SomeContext>();
services.AddScoped<IUnitOfWork, UnitOfWork>();
Now in my controller I have a long running task that happens and after it is finished I need to do some cleanup but I want to go ahead and respond to the request so it doesn't have to wait for these long running tasks to complete
[Route("api/[controller]")]
[ApiController]
public class ValuesController : ControllerBase
{
private readonly IUnitOfWork _uow;
public ValuesController(IUnitOfWork uow)
{
_uow = uow;
}
[Route("Test")]
public async Task<IActionResult> GetTest()
{
Task myTask = SomeLongRunningThing();
try
{
return Ok();
}
finally
{
Response.OnCompleted(async () =>
{
Task continueTask = myTask.ContinueWith(async (task) =>
{
await Task.Delay(5000);
Console.WriteLine("Checking if context is disposed...");
Console.WriteLine(_uow.GetContextDisposed());
});
await myTask;
await continueTask;
});
}
Console.WriteLine("End of route");
}
private Task SomeLongRunningThing()
{
return Task.Run(() =>
{
Task.Delay(10000);
});
}
}
The output shows
Dispose being called on Context
Dispose being called on Context
Dispose being called on Context
Dispose being called on Context
Checking if context is disposed...
True
What could be causing the context to be disposed before the route is fully completed?
I've tried messing with the lifetimes but it doesn't seem any lifetime helps the situation.
Version Stuff
.net core 3.1 MVC
Running on Windows 10
Thanks
Figured out something that works for my use case, I think...
I inject IServiceProvider into my controller as well
private readonly IUnitOfWork _uow;
private readonly IServiceProvider _services;
public ValuesController(IUnitOfWork uow, IServiceProvider services)
{
_uow = uow;
_services = services;
}
Then during the Task.Run(() => {}) and ContinueWith(async (task) => {}) I can use it to create a new scope and get an IUnitOfWork
private Task SomeLongRunningThing(OperationContext context)
{
return Task.Run(() =>
{
using (var scope = _services.CreateScope())
{
IUnitOfWork uow = scope.ServiceProvider.GetRequiredService<IUnitOfWork>();
OperationContext.Current = context;
Task.Delay(10000);
}
});
}
Task continueTask = myTask.ContinueWith(async (task) =>
{
using(var scope = _services.CreateScope())
{
IUnitOfWork uow = scope.ServiceProvider.GetRequiredService<IUnitOfWork>();
await Task.Delay(5000);
Console.WriteLine("Checking if context is disposed...");
Console.WriteLine(uow.GetContextDisposed());
}
});
So, I have for example this Laravel Resource Controller code like this:
class BaseAPIController extends Controller
{
public function index()
{
return self::$model->all();
}
}
So, I was trying to do like that in ASP.NET C#:
[ApiController]
public class BaseAPIController<T> : ControllerBase
{
[HttpGet]
public ActionResult<IEnumerable<T>> Get()
{
using (ExamRTContext db = new ExamRTContext())
{
return db.${typeof(T).Name}.Select(x => x);
}
}
}
But I don't have any idea how to do like that.
So, Let say I just wanted to do simple CRUD in 3 tables. All operation is same, for example Get() is used to get all data from that model.
Instead of writing it 3 times, I wanted to just write it once and extend it to each model controller.
Any idea how to do that?
C# does not allow you to compose expressions at runtime like that.
However, EF has an API to do this.
You're looking for .Set<T>().
If you want to perform simple CRUD operations with entity framework you could create a generic repository.
Repository:
public class GenericRepository<TEntity, TContext>
where TContext : DbContext
where TEntity : class
{
protected readonly TContext context;
public GenericRepository(TContext context)
{
this.context = context;
}
public virtual async Task Add(TEntity model)
{
await context.Set<TEntity>().AddAsync(model);
await context.SaveChangesAsync();
}
public virtual async Task<TEntity> Get(int id)
{
return await context.Set<TEntity>().FindAsync(id);
}
public virtual async Task<IEnumerable<TEntity>> GetAll()
{
return await context.Set<TEntity>().ToListAsync();
}
public virtual async Task<TEntity> FindFirstBy(Func<TEntity,bool> predicate)
{
return await Task.Run(()=> context.Set<TEntity>().FirstOrDefault(predicate));
}
public virtual async Task<IEnumerable<TEntity>> FilterBy(Func<TEntity,bool> predicate)
{
return await Task.Run(()=> context.Set<TEntity>().Where(predicate).ToList());
}
public virtual async Task Update()
{
await context.SaveChangesAsync();
}
public virtual async Task Remove(TEntity model)
{
context.Set<TEntity>().Remove(model);
await context.SaveChangesAsync();
}
}
To be able to use it you just have to inject it in the controller specifying the Entity Type and the Context. In your example it would be like:
Controller Base:
[ApiController]
public class BaseAPIController<T> : ControllerBase
{
protected readonly GenericReposoitory<T,ExamRTContext> repository;
public BaseAPIController(GenericRepository<T,ExamRTContext> repository) {
this.repository = repository;
}
[HttpGet]
public ActionResult<IEnumerable<T>> Get()
{
var entities = repository.GetAll();
if (entities!= null) {
return Ok(entities);
}
return NotFound();
}
}
In Startup:
services.AddTransient(typeof(GenericRepository<,>), typeof(GenericRepository<,>));
I am building an ASP.NET Core API. I have an action that I want to be essentially identical across a set of controllers. So, I created the EntityController that those controllers inherit from as below.
Note: The ellipsis used in both classes below represent many more actions and their related services following the same pattern omitted for simplicity.
public class EntityController : BaseController
{
protected readonly SeedService SeedService;
protected EntityController(IMemoryCache memoryCache, SeedService seedService) : base(memoryCache)
{
SeedService = seedService;
}
[HttpGet]
public async Task<IActionResult> Seed()
{
var controllerName = ControllerContext.RouteData.Values["controller"].ToString();
return await GetSeed(controllerName);
}
private async Task<IActionResult> GetSeed(string controllerName)
{
switch (controllerName)
{
case "lists":
return await MemoryCache.GetOrCreateAsync(CacheKeys.Entry, async entry =>
{
entry.SlidingExpiration = TimeSpan.FromSeconds(3);
return Json(await SeedService.GetAllFilterLists());
});
case "languages":
return await MemoryCache.GetOrCreateAsync(CacheKeys.Entry, async entry =>
{
entry.SlidingExpiration = TimeSpan.FromSeconds(3);
return Json(await SeedService.GetAllLanguages());
});
...
default:
return await Task.FromResult(NotFound());
}
}
}
Here are the service methods that these actions call:
public class SeedService
{
private readonly FilterListsDbContext filterListsDbContext;
public SeedService(FilterListsDbContext filterListsDbContext)
{
this.filterListsDbContext = filterListsDbContext;
}
public async Task<IEnumerable<FilterListSeedDto>> GetAllFilterLists()
{
return await filterListsDbContext.Set<FilterList>().ProjectTo<FilterListSeedDto>().ToListAsync();
}
public async Task<IEnumerable<LanguageSeedDto>> GetAllLanguages()
{
return await filterListsDbContext.Set<Language>().ProjectTo<LanguageSeedDto>().ToListAsync();
}
...
}
How can I use generics (or alternative) to reduce this copy/paste duplication? I tried using something like a Dictionary<string, Type> to lookup the Type dynamically from the controller name, but I am not sure how the resulting GetAll<T>() method in SeedService would look? Below doesn't work because the method depends on the types of both the entity and DTO models for the AutoMapper projection.
public async Task<IEnumerable<T>> GetAll<T>()
{
return await filterListsDbContext.Set<T>().ProjectTo<T>().ToListAsync();
}
You could easily remove all that boilerplate code into a single generic method:
public async Task<IEnumerable<TResult>> GetAll<TEntry, TResult>() where TEntry : class
{
return await filterListsDbContext.Set<TEntry>()
.ProjectTo<TResult>()
.ToListAsync();
}
Since you are returning an IEnumerable, you may want to change to .ToArrayAsync(). Also, since you are projecting to non-entities, and hence changes won't be picked up by the context, you could go further and add .AsNoTracking() to avoid adding the entities to the context:
public async Task<IEnumerable<TResult>> GetAll<TEntry, TResult>() where TEntry : class
{
return await filterListsDbContext.Set<TEntry>()
.AsNoTracking()
.ProjectTo<TResult>()
.ToArrayAsync();
}
As I mentioned in the comments, you could put that in a base controller and do something like this:
public class BaseController<TEntity, TViewModel>
{
public async Task<IEnumerable<TViewModel>> GetAll()
{
return await filterListsDbContext.Set<TEntity>()
.AsNoTracking()
.ProjectTo<TViewModel>()
.ToArrayAsync();
}
}
public class LanguageController : BaseController<Language, LanguageSeedDto>
{
(in some action)
var data = await GetAll();
}
I have a WebApi controller which calls a third party API in asynchronous mode.
All works ok and now I want to sort the result in a separate action method.
Now, when I call the API, the callback with the result never happens after running "await client.GetAsycn(...)" in the DAL. What am I missing?
This is my API controller:
// GET api/lookup
[ResponseType(typeof(RestaurantModel))]
public async Task<IHttpActionResult> Get(string outcode)
{
if (string.IsNullOrEmpty(outcode)) throw new ArgumentNullException(nameof(outcode));
var result = await _repository.GetRestaurantsByOutcode(outcode);
return Ok(new RestaurantModel()
{
Result = result
});
}
// GET api/sorted
[System.Web.Http.Route("~/api/sorted")]
public List<Restaurant> GetSorted(string outcode)
{
if (string.IsNullOrEmpty(outcode)) throw new ArgumentNullException(nameof(outcode));
return _repository.GetSortedRestaurantsByOutcode(outcode);
}
This is my repository with a new method to sort the result:
public class RestaurantRepository : IRestaurantRepository
{
private readonly IContext _context;
public RestaurantRepository(IContext context)
{
_context = context;
}
public Task<ApiResult> GetRestaurantsByOutcode(string outcode)
{
return _context.GetRestaurantsByOutcode(outcode);
}
public List<Restaurant> GetSortedRestaurantsByOutcode(string outcode)
{
return _context.GetRestaurantsByOutcode(outcode).Result.Restaurants
.OrderBy(x => x.Name).ToList();
}
}
This is my DAL to call the third party API:
public async Task<ApiResult> GetRestaurantsByOutcode(string outcode)
{
using (var client = new HttpClient())
{
ConfigureHttpClient(client);
var response = await client.GetAsync(
$"restaurants?q={WebUtility.UrlEncode(outcode)}");
return response.IsSuccessStatusCode
? await response.Content.ReadAsAsync<ApiResult>()
: null;
}
}
You have a mix-match of sometimes you use async/await and other times you don't. Async / await (can and does by default) ensures that the call resumes on the calling thread so the context is resulted. You need to allign your code so you make use of the async/await in the whole stack. Otherwise you are creating a deadlock for your self.
[System.Web.Http.Route("~/api/sorted")]
// missing async in signature (not good if you are calling it with await in your controller)
public async Task<List<Restaurant>> GetSorted(string outcode)
{
if (string.IsNullOrEmpty(outcode)) throw new ArgumentNullException(nameof(outcode));
// added await in call
return await _repository.GetSortedRestaurantsByOutcode(outcode);
}
DAL
public class RestaurantRepository : IRestaurantRepository
{
private readonly IContext _context;
public RestaurantRepository(IContext context)
{
_context = context;
}
// added async and await
public async Task<ApiResult> GetRestaurantsByOutcode(string outcode)
{
return await _context.GetRestaurantsByOutcode(outcode);
}
// added async and await
public async Task<List<Restaurant>> GetSortedRestaurantsByOutcode(string outcode)
{
// here you were not using await but then using result even though you were calling into a method marked as async which in turn used an await. this is where you deadlocked but this the fix.
return (await _context.GetRestaurantsByOutcode(outcode)).Restaurants
.OrderBy(x => x.Name).ToList();
}
}
I have a WebApi controller that has services injected by AutoFac in the OWIN Startup class
builder.Register(c => new MyEntities()).InstancePerRequest();
I have also tried
builder.Register(c => new MyEntities()).InstancePerLifetimeScope();
In a controller action I call a service method to create a new record, pass the id created to an external api through HttpClient to get some more data, then update the new record with some return data.
[HttpPost, Route("")]
public async Task<IHttpActionResult> MyControllerAction(MyModel model)
{
var id = await _MyService.CreateNewThing(model.SomeId);
var externalData = await CallExternalApiThroughHttpClient(id);
await _MyService.UpdateNewThing(id, externalData);
return Ok();
}
service code
public class MyService : IMyService
{
private MyEntities _context;
public MyService(MyEntities context)
{
_context = context;
}
public async Task<int> CreateNewThing(int someId)
{
var thing = new Thing
{
SomeId = someId
};
_context.Things.Add(thing);
await _context.SaveChangesAsync();
return thing.Id;
}
public async Task UpdateNewThing(int id, string externalDataField)
{
var thing = await _context.Things.SingleOrDefaultAsync(o => o.Id == id);
if (thing == null)
{
throw new ServiceNotFoundException("Thing " + transactionId + " not found");
}
thing.ExternalDataField= externalDataField;
await _context.SaveChangesAsync();
}
}
But I get an InvalidOperationException in UpdateNewThing var thing = await _context.Things.SingleOrDefaultAsync(o => o.Id == id);
System.InvalidOperationException: The connection was not closed. The connection's current state is connecting.
It seems like I have to give up either injecting the context, async/await or use something like a contextfactory; unless anyone can spot something simple I have missed that would let me continue with this design.
Your code looks fine in a single-threaded context. However, DbContext is not thread safe, and I suspect what is happening is you're executing CreateNewThing() on one thread, and the task scheduler is in this case executing UpdateNewThing() on a different thread.
Either way, a better metaphor is to use a context factory, which you inject into your IMyService in this case, and then for every IMyService method you create a new MyEntities context in a using() block.
DbContext's are cheap to create and this is how they are intended to be used; long-lived contexts are almost always incorrect usage.
Edit 1 - example context factory as requested. I tend to implement a generic factory that can create multiple contexts, but that's probably moving outside the scope of this question.
public interface IMyEntitiesFactory
{
MyEntities Create();
}
public class MyEntitiesFactory : IMyEntitiesFactory
{
MyEntities IMyEntitiesFactory.Create()
{
return new MyEntities();
}
}
// For use with unit tests; e.g. pass a mock object to the constructor.
public class TestMyEntitiesFactory : IMyEntitiesFactory
{
private readonly MyEntities _value;
public TestMyEntitiesFactory(MyEntities value)
{
_value = value;
}
MyEntities IMyEntitiesFactory.Create()
{
return _value;
}
}