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

Answer 1

I had the same problem and what it is the I had to make sure that the name of the connection matches:

      services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
        services.AddDbContext<MyContext>(options => options.UseSqlServer(Configuration["ConnectionStrings:DefaultConnection"]));

which ****ConnectionStrings:DefaultConnection*** it was where I had the whole problem. Make sure that is the same in Startup.cs and appsettings.json(appsettings.Development.json in Vs 2019)

After I fixed this, everything was fine.

Answer 2

I had a similar issue. I had a typo in my appsettings.json. Changing ConnectionsStrings to ConnectionStrings did it for me!

Answer 3

This worked flawlessly for me:

public IConfiguration Configuration;
public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<ApplicationDbContext.ApplicationDbContext>(options => 
            //options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
            options.UseSqlServer("Server=serverAddress; Database=dbName; user=username; password=pswd"));
}

The commented part is just as reference where to replace.

Answer 4

I had had a similar issue because of the following reasons:

• appsettings.json was not included in the project
• I was running the project from the path which did not contain appsettings.json

Answer 5

I had a similar problem after trying to use new created project for ASP.NET Core 2.0 Web Api. As far as I found, the cause of the problem was that application settings specified for development environment were not added. I fixed it by updating startup file to the following:

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

In my case program class looks like the following:

public class Program
{
    public static void Main(string[] args)
    {
        BuildWebHost(args).Run();
    }

    public static IWebHost BuildWebHost(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .UseStartup<Startup>()
            .Build();
}

Answer 6

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.