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 such issue when load tesing the service (I recommend it to all) and had ~3/1000 requests with errors, so I changed

services.AddDbContextPool<AppDbContext>(options =>
options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

to

string connectionString = Configuration.GetConnectionString("DefaultConnection");
services.AddDbContextPool<AppDbContext>(options =>
options.UseSqlServer(connectionString));

So it reads connections string 1 time and doesn't use Configuration on every request. And now 100% requests are successful. But it seems to be a bug in .Net Core

Answer 2

If you are using an IDesignTimeDbContextFactory, you will need to add a default constructor to it with no parameters. Try something like this:

public DbContextFactory()
{
    IConfigurationRoot configuration = new ConfigurationBuilder()
        .SetBasePath(Directory.GetCurrentDirectory())
        .AddEnvironmentVariables()
        .AddJsonFile("appsettings.json", false, true)
        .Build();

    _connectionString = configuration.GetConnectionString("ConnectionStringName");
}

Answer 3

I had this problem due to a difference in connectionstring of appsetting.json file, and the GetConnectionString(connectionstrings) parameter in startup.cs. Once I removed extra s in startup.cs, the problem disappeared.

Answer 4

This problem occurred when the connectionstring can't be found.

Probably you have following codes 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 5

I had the same problem, because I was using the default value in Startup.cs. I just edited Configuration property from:

public IConfiguration Configuration { get; }

to:

public IConfiguration Configuration;

and it worked! If someone say why would be appreciated.

Answer 6

My problem was when I was trying to run App.dll within netcoreapp2.1 folder, but the right folder is netcoreapp2.1\publish\