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(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.