在 httpContextAccessor.HttpContext 返回空值

Question

我们覆盖 SaveChangesAsync() 以自动更新 DateCreated、CreatedBy、LastDateModified 和 LastModifiedBy。使用 CreatedBy 和 LastModifiedBt，我们需要 Identity 的 User Id。

在 ApplicationDbContext 的构造函数中，我们添加了如下内容：

_userName = httpContextAccessor.HttpContext.User.Identity.Name; //_userID = userManager.GetUserId(httpContext.HttpContext.User);

.. 并始终在此 httpContextAccessor.HttpContext 中得到 null。有任何想法吗？我们在下面包含了来源。

环境：

.NET 核心 2.1

SQL 服务器

ApplicationDBContext.cs:

using System;
using System.Collections.Generic;
using System.Text;
using Microsoft.AspNetCore.Identity.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore;
using AthlosifyWebArchery.Models;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Linq.Expressions;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Identity;

namespace AthlosifyWebArchery.Data
{
    public class ApplicationDbContext : IdentityDbContext<ApplicationUser, ApplicationRole, string>
    {
        private readonly string _userID;
        private readonly string _userName;


        public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options,
                IHttpContextAccessor httpContextAccessor
                )
        : base(options)
        {
            _userName = httpContextAccessor.HttpContext.User.Identity.Name;

            //_userID = userManager.GetUserId(httpContext.HttpContext.User);

        }

        public DbSet<AthlosifyWebArchery.Models.TournamentBatchItem> TournamentBatchItem { get; set; }
        public DbSet<AthlosifyWebArchery.Models.TournamentBatch> TournamentBatch { get; set; }

        public virtual DbSet<AthlosifyWebArchery.Models.Host> Host { get; set; }

        public DbSet<AthlosifyWebArchery.Models.HostApplicationUser> HostApplicationUser { get; set; }

        protected override void OnModelCreating(ModelBuilder builder)
        {
            base.OnModelCreating(builder);

            foreach (var entityType in builder.Model.GetEntityTypes())
            {
                // 1. Add the IsDeleted property
                entityType.GetOrAddProperty("IsDeleted", typeof(bool));

                // 2. Create the query filter

                var parameter = Expression.Parameter(entityType.ClrType);

                // EF.Property<bool>(post, "IsDeleted")
                var propertyMethodInfo = typeof(EF).GetMethod("Property").MakeGenericMethod(typeof(bool));
                var isDeletedProperty = Expression.Call(propertyMethodInfo, parameter, Expression.Constant("IsDeleted"));

                // EF.Property<bool>(post, "IsDeleted") == false
                BinaryExpression compareExpression = Expression.MakeBinary(ExpressionType.Equal, isDeletedProperty, Expression.Constant(false));

                // post => EF.Property<bool>(post, "IsDeleted") == false
                var lambda = Expression.Lambda(compareExpression, parameter);

                builder.Entity(entityType.ClrType).HasQueryFilter(lambda);
            }


            // Many to Many relationship

            builder.Entity<HostApplicationUser>()
                .HasKey(bc => new { bc.HostID, bc.Id });


            builder.Entity<HostApplicationUser>()
                .HasOne(bc => bc.Host)
                .WithMany(b => b.HostApplicationUsers)
                .HasForeignKey(bc => bc.HostID);

            builder.Entity<HostApplicationUser>()
                .HasOne(bc => bc.ApplicationUser)
                .WithMany(c => c.HostApplicationUsers)
                .HasForeignKey(bc => bc.Id);

        }

        public override int SaveChanges(bool acceptAllChangesOnSuccess)
        {
            OnBeforeSaving();
            return base.SaveChanges(acceptAllChangesOnSuccess);
        }

        public override Task<int> SaveChangesAsync(bool acceptAllChangesOnSuccess, CancellationToken cancellationToken = default(CancellationToken))
        {
            OnBeforeSaving();
            return base.SaveChangesAsync(acceptAllChangesOnSuccess, cancellationToken);
        }

        private void OnBeforeSaving()
        {
            // Added
            var added = ChangeTracker.Entries().Where(v => v.State == EntityState.Added && typeof(IBaseEntity).IsAssignableFrom(v.Entity.GetType())).ToList();

            added.ForEach(entry =>
            {
                ((IBaseEntity)entry.Entity).DateCreated = DateTime.UtcNow;
                ((IBaseEntity)entry.Entity).CreatedBy = _userID;
                ((IBaseEntity)entry.Entity).LastDateModified = DateTime.UtcNow;
                ((IBaseEntity)entry.Entity).LastModifiedBy = _userID;
            });

            // Modified
            var modified = ChangeTracker.Entries().Where(v => v.State == EntityState.Modified && 
            typeof(IBaseEntity).IsAssignableFrom(v.Entity.GetType())).ToList();

            modified.ForEach(entry =>
            {
                ((IBaseEntity)entry.Entity).LastDateModified = DateTime.UtcNow;
                ((IBaseEntity)entry.Entity).LastModifiedBy = _userID;
            });

            // Deleted
            //var deleted = ChangeTracker.Entries().Where(v => v.State == EntityState.Deleted &&
            //typeof(IBaseEntity).IsAssignableFrom(v.Entity.GetType())).ToList();

            var deleted = ChangeTracker.Entries().Where(v => v.State == EntityState.Deleted).ToList();

            deleted.ForEach(entry =>
            {
                ((IBaseEntity)entry.Entity).DateDeleted = DateTime.UtcNow;
                ((IBaseEntity)entry.Entity).DeletedBy = _userID;
            });

            foreach (var entry in ChangeTracker.Entries()
                                    .Where(e => e.State == EntityState.Deleted &&
                                    e.Metadata.GetProperties().Any(x => x.Name == "IsDeleted")))
            {
                switch (entry.State)
                {
                    case EntityState.Added:
                        entry.CurrentValues["IsDeleted"] = false;
                        break;

                    case EntityState.Deleted:
                        entry.State = EntityState.Modified;
                        entry.CurrentValues["IsDeleted"] = true;
                        break;
                }
            }
        }
    }



}

Startup.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using AthlosifyWebArchery.Data;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using AthlosifyWebArchery.Models;
using DinkToPdf.Contracts;
using DinkToPdf;

namespace AthlosifyWebArchery
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            //services.AddHttpContextAccessor();

            services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
            services.AddSingleton(typeof(IConverter), new SynchronizedConverter(new PdfTools()));

            services.Configure<CookiePolicyOptions>(options =>
            {
                // This lambda determines whether user consent for non-essential cookies is needed for a given request.
                options.CheckConsentNeeded = context => true;
                options.MinimumSameSitePolicy = SameSiteMode.None;
            });

            services.AddDbContext<ApplicationDbContext>(options =>
                options.UseSqlServer(
                    Configuration.GetConnectionString("DefaultConnection")));

            // Extended Application User from IdentityUser 
            // and ApplicationRole from IdentityRole

            services.AddIdentity<ApplicationUser, ApplicationRole>(
                options => options.Stores.MaxLengthForKeys = 128)
                .AddEntityFrameworkStores<ApplicationDbContext>()
                .AddDefaultUI()
                .AddDefaultTokenProviders();

            services.AddMvc()
                .AddRazorPagesOptions(options =>
                {
                    options.Conventions.AuthorizeFolder("/Tournaments");
                    options.Conventions.AuthorizeFolder("/TournamentAtheletes");
                    options.Conventions.AuthorizeFolder("/TournamentBatches");
                    options.Conventions.AuthorizeFolder("/TournamentContingents");
                    options.Conventions.AuthorizeFolder("/Admin");
                    //options.Conventions.AuthorizeFolder("/Private");
                    //options.Conventions.AllowAnonymousToPage("/Private/PublicPage");
                    //options.Conventions.AllowAnonymousToFolder("/Private/PublicPages");
                })
                .SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env, 
                                ApplicationDbContext context,
                                RoleManager<ApplicationRole> roleManager,
                                UserManager<ApplicationUser> userManager)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
                app.UseDatabaseErrorPage();
            }
            else
            {
                app.UseExceptionHandler("/Error");
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseStaticFiles();
            app.UseCookiePolicy();

            app.UseAuthentication();

            app.UseMvc();

            //UserManagerInitialData.Initialize(context, userManager, roleManager).Wait();

        }


    }
}

Answer 1

HttpContext 只在请求期间有效。当 .NET Core 为调用 Configure 创建 ApplicationDbContext class 时，没有有效的上下文。

您需要在 DbContext 构造函数中存储对 IHttpContextAccessor 的引用，然后您可以使用该变量访问 HttpContext 属性 18=]方法。

例如：

public class ApplicationDbContext : IdentityDbContext<ApplicationUser, ApplicationRole, string>
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options,
            IHttpContextAccessor httpContextAccessor
            )
    : base(options)
    {
        _httpContextAccessor = httpContextAccessor;
    }

   ....
}

然后，在您的 OnBeforeSaving() 方法中：

private void OnBeforeSaving()
{
    var userName = _httpContextAccessor.HttpContext.User.Identity.Name;

    ...
}

将 HttpContext 视为电话phone。如果你在没有人打电话时拿起 phone 那么就没有 context 即它是空的。当有人打电话时，您就有了一个有效的 context。这与网络调用的原理相同。 Startup 中的 Configure 方法不是网络调用，因此没有 HttpContext.

来自另一个站点：

HttpContext object will hold information about the current http request. In detail, HttpContext object will be constructed newly for every request given to an ASP.Net application and this object will hold current request specific informations like Request, Response, Server, Session, Cache, User and etc. For every request, a new HttpContext object will be created which the ASP.Net runtime will use during the request processing. A new HttpContext object will be created at the beginning of a request and destroyed when the request is completed.

Answer 2

上面的答案解释得很好，但我想强调另一种情况，它也可能为空。例如：

public class SomeClass
{
   SomeClass(IHttpContextAccessor accessor) {}
   IActionResult SomeMethod()
   {
      _ = Task.Run(() =>
          {
             // use accessorHere
          }
   return Ok();
  }
}

有可能在 Thread 可以访问 IHttpContextAccessor 之前返回 Api 调用并且 IHttpConextAccessor.HttpContext 有可能为空。

因此，如果我们可以从 ex: userclaims 的 HttpContext 中获取所需的值，并将它们作为单独的对象传递给所需的函数，那就更好了。

在 httpContextAccessor.HttpContext 返回空值

Returning null on httpContextAccessor.HttpContext

.net-core

asp.net-core

asp.net-core-2.0