asp.net core 2.0 - Value cannot be null. Parameter name: connectionString

Question

I had the following error in package manager console when Add-Migration

Value cannot be null. Parameter name: connectionString

This is my startup:

namespace MyProject {     public class Startup     {         public IConfiguration Configuration { get; set; }         public Startup(IConfiguration config)         {             Configuration = config;         }          public void ConfigureServices(IServiceCollection services)         {             services.AddDbContextPool<AppDbContext>(options =>                              options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));             services.AddTransient<IDevRepo, DevRepo>();             services.AddMvc();             services.AddMemoryCache();             services.AddSession();         }          public void Configure(IApplicationBuilder app, IHostingEnvironment env)         {             if (env.IsDevelopment())             {                 app.UseDeveloperExceptionPage();             }             app.UseStatusCodePages();             app.UseStaticFiles();             app.UseMvcWithDefaultRoute();             app.Run(async (context) =>             {                 await context.Response.WriteAsync(Configuration["Message"]);             });         }     } } 

program class:

public class Program {     public static void Main(string[] args)     {         BuildWebHost(args).Run();     }      public static IWebHost BuildWebHost(string[] args) =>         WebHost.CreateDefaultBuilder(args)             .ConfigureAppConfiguration((context, builder) => builder.SetBasePath(context.HostingEnvironment.ContentRootPath)                        .AddJsonFile("appsettings.json")                        .Build())              .UseStartup<Startup>()             .Build(); } 

appsettings.json:

{   "Message": "Hello World",   "ConnectionStrings": {     "DefaultConnection": "Server=(localdb)\\MSSQLLocalDB;Database=NotMyFault;Trusted_Connection=True;MultipleActiveResultSets=true"   } } 

Interestingly if I run the app, it displays "Hello World", but when add migration it cannot find connectionString. Can someone please shed some lights here? Thanks.

Answer 1

This problem occurred when the connection string can't be found.

Probably you have the following code in Startup class:

public void ConfigureServices(IServiceCollection services)     {         services.AddDbContext<BenchmarkContext>(options =>             options.UseSqlServer(Configuration.GetConnectionString("yourConnectionString name from appsettings.json")));     } 

These methods solve your problem:

1- Instead of Configuration.GetConnectionString("yourConnectionString name from appsettings.json") just put your connectionstring.

public void ConfigureServices(IServiceCollection services)     {         services.AddDbContext<BenchmarkContext>(options =>   options.UseSqlServer("Data Source=.;Initial Catalog=Benchmark;Persist Security Info=True;User ID=****;Password=****"));     } 

2- If you are going to use the Configuration file add these codes to Startup class:

public Startup(IConfiguration configuration)     {         Configuration = configuration;     } public IConfiguration Configuration;  public void ConfigureServices(IServiceCollection services)     {         services.AddDbContext<BenchmarkContext>(options =>             options.UseSqlServer(Configuration.GetConnectionString("TestConnection")));     } 

Appsetting.json file:

{   "ConnectionStrings": {     "TestConnection": "Data Source=.;Initial Catalog=Benchmark;Persist Security Info=True;User ID=****;Password=****"   } } 

After that execute 'add-migration name' command in Package Manager Console

Answer 2

I had the same issue, but my solution was a lot simpler. All I did was to change the order of the appsettings.json from:

{   "Message": "Hello World",   "ConnectionStrings": {     "DefaultConnection": "Server=(localdb)\\MSSQLLocalDB;Database=NotMyFault;Trusted_Connection=True;MultipleActiveResultSets=true"   } } 

to:

{    "ConnectionStrings": {     "DefaultConnection": "Server=(localdb)\\MSSQLLocalDB;Database=NotMyFault;Trusted_Connection=True;MultipleActiveResultSets=true"   },   "Message": "Hello World" } 

I have a suspicion that there is a sequence/order of parameters in the appsettings.json file.