InvalidOperationException：沒有為此DbContext配置數據庫提供程序

Question

context = new ApplicationDbContext();
context.Clients.Add(item);

InvalidOperationException：沒有為此DbContext配置數據庫提供程序。 可以通過重寫DbContext.OnConfiguring方法或在應用程序服務提供程序上使用AddDbContext來配置提供程序。 如果使用AddDbContext，則還應確保DbContext類型在其構造函數中接受DbContextOptions對象，並將其傳遞給DbContext的基本構造函數。

public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
    {
        public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
            : base(options)
        {

        }

        public ApplicationDbContext()
        {

        }

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

        }

        public DbSet<Client> Clients { get; set; }

啟動

public class Startup
    {
        public Startup(IHostingEnvironment env)
        {
            var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
                .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true);

            if (env.IsDevelopment())
            {
                // For more details on using the user secret store see https://go.microsoft.com/fwlink/?LinkID=532709
                builder.AddUserSecrets<Startup>();
            }

            builder.AddEnvironmentVariables();
            Configuration = builder.Build();
        }

        public IConfigurationRoot Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            // Add framework services.
            services.AddDbContext<ApplicationDbContext>(options =>
                options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

            services.AddIdentity<ApplicationUser, IdentityRole>()
                .AddEntityFrameworkStores<ApplicationDbContext>()
                .AddDefaultTokenProviders();

            services.AddMvc();

            // Add application services.
            services.AddTransient<IEmailSender, AuthMessageSender>();
            services.AddTransient<ISmsSender, AuthMessageSender>();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            loggerFactory.AddConsole(Configuration.GetSection("Logging"));
            loggerFactory.AddDebug();

            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
                app.UseDatabaseErrorPage();
                app.UseBrowserLink();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
            }

            app.UseStaticFiles();

            app.UseIdentity();

            // Add external authentication middleware below. To configure them please see https://go.microsoft.com/fwlink/?LinkID=532715

            app.UseMvc(routes =>
            {
                routes.MapRoute(
                    name: "default",
                    template: "{controller=Home}/{action=Index}/{id?}");
            });
        }
    }

更新

我加了

// Startup.ConfigureServices
public void ConfigureServices(IServiceCollection services)
    {
        // Add framework services.
        services.AddDbContext<ApplicationDbContext>(options =>
            options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

        //////my=>
        services.AddDbContext<DbContext>(config =>
        {
            config.UseSqlServer(Configuration.GetConnectionString("Default"));
        });

並在您的appsettings.json中進行配置

    {
  "ConnectionStrings": {
    "DefaultConnection": "Server=(localdb)\\mssqllocaldb;Database=aspnet-WebApplicationCore-42a4ac05-477c-4ea7-b286-87423170b48a;Trusted_Connection=True;MultipleActiveResultSets=true",
    "Default": "Server=(localdb)\\mssqllocaldb;Database=aspnet-WebApplicationCore-42a4ac05-477c-4ea7-b286-87423170b48a;"
  },
  "Logging": {
    "IncludeScopes": false,
    "LogLevel": {
      "Default": "Warning"
    }
  }
}

我單擊了appsettings.json文件，並將屬性窗口中的屬性更改為“ Build Action：Content”和“ CopyToOutputDirectory：Copy Always”

<ItemGroup>
  <Content Update="appsettings.json">
    <CopyToOutputDirectory>Always</CopyToOutputDirectory>
  </Content>
</ItemGroup>

錯誤未解決

新錯誤：

var result = await _userManager.CreateAsync(user, model.Password);

處理請求時發生未處理的異常。 SqlException：建立與SQL Server的連接時發生與網絡相關或特定於實例的錯誤。 服務器未找到或無法訪問。 驗證實例名稱正確，並且已將SQL Server配置為允許遠程連接。 （提供程序：SQL網絡接口，錯誤：50-發生本地數據庫運行時錯誤。ВовремязапускаэкземпляраLocalDB版本：SQL Server。）

System.Data.SqlClient.SqlInternalConnectionTds..ctor（DbConnectionPoolIdentity身份，SqlConnectionString connectionOptions，對象providerInfo，bool redirectedUserInstance，SqlConnectionString userConnectionOptions，SessionData reconnectSessionData，bool applyTransientFaultHandling）

Answer 1

沒有參數化構造函數或對OnConfiguring的覆蓋，您無法實例化OnConfiguring 。

您有兩種選擇：

1. 通過DI將DbContextOptions<ApplicationDbContext>傳遞給您的ApplicationDbContext 。 這是通過在startup.cs中配置ApplicationDbContext並解決它（不使用new關鍵字！！！）來完成的。

    // Startup.ConfigureServices services.AddDbContext<DbContext>(config => { config.UseSqlServer(Configuration.GetConnectionString("Default")); }); 

   並在您的appsettings.json中進行配置

    { "ConnectionStrings": { "Default": "YourSQLConnectionStringHere" } } 

2. 不建議使用，因為它需要對連接字符串進行硬編碼，因此方法是在DbContext中配置它

    public class ApplicationDbContext { public ApplicationDbContext(DbContextOptions options) : base(options) { } // The call of the base constructor via ": base()" is still required public ApplicationDbContext(DbContextOptions options) : base() { } protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) { optionsBuilder.UseSqlServer(Configuration.GetConnectionString("connectionStringHere")); base.OnConfiguring(optionsBuilder); } } 

更新

為了回應評論，您需要添加

<ItemGroup>
  <Content Update="appsettings.json">
    <CopyToOutputDirectory>Always</CopyToOutputDirectory>
  </Content>
</ItemGroup>

為了將appsettings.json復制到輸出目錄。 或者，只需單擊appsettings.json文件，然后將屬性窗口中的屬性更改為“ Build Action：Content”和“ CopyToOutputDirectory：Copy Always”