标签:asp-net-web-api2 dependency-injection unity-container c
我在使用依赖注入方面还很陌生,我认为我必须忽略一些非常简单的事情.
我有一个Web API项目,在这里注册通用存储库.存储库在其构造函数中将dbContext作为参数.
我发现很奇怪的行为是,我可以对服务进行一次成功调用,但是随后的任何调用都告诉我dbcontext已被处置.我确实有一个using语句,但这应该不是问题,因为DI应该为每个Web请求创建依赖项的新实例(尽管我可能错了).
这是我的通用存储库:
public class GenericRepository<T> : IGenericRepository<T> where T : class
{
internal DbContext _context;
internal DbSet<T> _dbSet;
private bool disposed;
public GenericRepository(DbContext context)
{
_context = context;
_dbSet = _context.Set<T>();
}
/// <summary>
/// This constructor will set the database of the repository
/// to the one indicated by the "database" parameter
/// </summary>
/// <param name="context"></param>
/// <param name="database"></param>
public GenericRepository(string database = null)
{
SetDatabase(database);
}
public void SetDatabase(string database)
{
var dbConnection = _context.Database.Connection;
if (string.IsNullOrEmpty(database) || dbConnection.Database == database)
return;
if (dbConnection.State == ConnectionState.Closed)
dbConnection.Open();
_context.Database.Connection.ChangeDatabase(database);
}
public virtual IQueryable<T> Get()
{
return _dbSet;
}
public virtual T GetById(object id)
{
return _dbSet.Find(id);
}
public virtual void Insert(T entity)
{
_dbSet.Add(entity);
}
public virtual void Delete(object id)
{
T entityToDelete = _dbSet.Find(id);
Delete(entityToDelete);
}
public virtual void Delete(T entityToDelete)
{
if (_context.Entry(entityToDelete).State == EntityState.Detached)
{
_dbSet.Attach(entityToDelete);
}
_dbSet.Remove(entityToDelete);
}
public virtual void Update(T entityToUpdate)
{
_dbSet.Attach(entityToUpdate);
_context.Entry(entityToUpdate).State = EntityState.Modified;
}
public virtual void Save()
{
_context.SaveChanges();
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (disposed)
return;
if (disposing)
{
//free managed objects here
_context.Dispose();
}
//free any unmanaged objects here
disposed = true;
}
~GenericRepository()
{
Dispose(false);
}
}
这是我的通用存储库接口:
public interface IGenericRepository<T> : IDisposable where T : class
{
void SetDatabase(string database);
IQueryable<T> Get();
T GetById(object id);
void Insert(T entity);
void Delete(object id);
void Delete(T entityToDelete);
void Update(T entityToUpdate);
void Save();
}
这是我的WebApiConfig:
public static class WebApiConfig
{
public static void Register(HttpConfiguration config)
{
// Web API configuration and services
var container = new UnityContainer();
container.RegisterType<IGenericRepository<Cat>, GenericRepository<Cat>>(new HierarchicalLifetimeManager(), new InjectionConstructor(new AnimalEntities()));
container.RegisterType<IGenericRepository<Dog>, GenericRepository<Dog>>(new HierarchicalLifetimeManager(), new InjectionConstructor(new AnimalEntities()));
config.DependencyResolver = new UnityResolver(container);
config.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));
// Web API routes
config.MapHttpAttributeRoutes();
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);
}
}
这是我的DependencyResolver(非常标准):
public class UnityResolver : IDependencyResolver
{
protected IUnityContainer container;
public UnityResolver(IUnityContainer container)
{
this.container = container ?? throw new ArgumentNullException(nameof(container));
}
public object GetService(Type serviceType)
{
try
{
return container.Resolve(serviceType);
}
catch (ResolutionFailedException)
{
return null;
}
}
public IEnumerable<object> GetServices(Type serviceType)
{
try
{
return container.ResolveAll(serviceType);
}
catch (ResolutionFailedException)
{
return new List<object>();
}
}
public IDependencyScope BeginScope()
{
var child = container.CreateChildContainer();
return new UnityResolver(child);
}
public void Dispose()
{
Dispose(true);
}
protected virtual void Dispose(bool disposing)
{
container.Dispose();
}
}
最后,这是给我带来麻烦的控制器的一部分:
public class AnimalController : ApiController
{
private readonly IGenericRepository<Cat> _catRepo;
private readonly IGenericRepository<Dog> _dogPackRepo;
public AnimalController(IGenericRepository<Cat> catRepository,
IGenericRepository<Dog> dogRepository)
{
_catRepo = catRepository;
_dogRepo = dogRepository;
}
[HttpGet]
public AnimalDetails GetAnimalDetails(int tagId)
{
var animalDetails = new animalDetails();
try
{
var dbName = getAnimalName(tagId);
if (dbName == null)
{
animalDetails.ErrorMessage = $"Could not find animal name for tag Id {tagId}";
return animalDetails;
}
}
catch (Exception ex)
{
//todo: add logging
Console.WriteLine(ex.Message);
animalDetails.ErrorMessage = ex.Message;
return animalDetails;
}
return animalDetails;
}
private string getAnimalName(int tagId)
{
try
{
//todo: fix DI so dbcontext is created on each call to the controller
using (_catRepo)
{
return _catRepo.Get().Where(s => s.TagId == tagId.ToString()).SingleOrDefault();
}
}
catch (Exception e)
{
//todo: add logging
Console.WriteLine(e);
throw;
}
}
}
_catRepo对象周围的using语句行为不符合预期.在我进行第一个服务调用后,_catRepo被处理掉了.在随后的调用中,我希望实例化一个新的_catRepo.但是,情况并非如此,因为我遇到的错误是关于dbcontext被处置的.
我试图将LifeTimeManager更改为其他可用的功能,但这无济于事.
我也开始沿着另一条路线走,通用存储库将采用第二个通用类,并从中实例化其自己的dbcontext.但是,当我这样做时,Unity找不到控制器的单参数构造函数.
我想,根据下面的评论,我真正需要的是一种基于每个请求实例化DbContext的方法.我不知道该怎么做.
任何提示将不胜感激.
解决方法:
让我们来看看您的注册:
container.RegisterType<IGenericRepository<Cat>, GenericRepository<Cat>>(
new HierarchicalLifetimeManager(),
new InjectionConstructor(new AnimalEntities()));
container.RegisterType<IGenericRepository<Dog>, GenericRepository<Dog>>(
new HierarchicalLifetimeManager(),
new InjectionConstructor(new AnimalEntities()));
您将在启动时创建两个AnimalEntities实例,但是这些实例在整个应用程序期间将被重用.这是一个terrible idea.您可能打算拥有one DbContext per request,但是InjectionConstructor包装的实例是一个常量.
您应该将配置更改为以下内容:
container.RegisterType<IGenericRepository<Cat>, GenericRepository<Cat>>(
new HierarchicalLifetimeManager());
container.RegisterType<IGenericRepository<Dog>, GenericRepository<Dog>>(
new HierarchicalLifetimeManager());
// Separate 'scoped' registration for AnimalEntities.
container.Register<AnimalEntities>(
new HierarchicalLifetimeManager()
new InjectionFactory(c => new AnimalEntities()));
这要简单得多,现在AnimalEntities也已注册为“作用域”.
这样做的好处是,一旦作用域(Web请求)结束,Unity现在将处置AnimalEntities.这样可以避免您必须对AnimalEntities的使用者实施IDisposable,如here和here所述.
标签:asp-net-web-api2,dependency-injection,unity-container,c 来源: https://codeday.me/bug/20191025/1930224.html
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