.NET Core Web API project and Entity Framework 6 null exception

Question

I am fairly new to both EF and .NET Core, but using a working project I was able to build a Core 2.0 Web API solution. The only issue is I am unable to get Entity Framework to instantiate on startup. I am receiving an error stating:

System.ArgumentNullException: Value cannot be null. Parameter name: connectionString

My Startup.cs file:

 public class Startup
{
    public Startup(IConfiguration configuration)
    {

        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

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

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.UseMvc();
    }
}

My validated JSON file:

  {
  "Logging": {
    "IncludeScopes": false,
    "Debug": {
      "LogLevel": {
        "Default": "Warning"
      }
    },
    "ConnectionStrings": {
      "dbc": "Server=cc;Initial Catalog=dd;Trusted_Connection=True;MultipleActiveResultSets=true"
    },
    "Console": {
      "LogLevel": {
        "Default": "Warning"
      }
    }
  }
}

UPDATE My Program.Cs

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

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

How is the configuration variable (that I'm assuming you are injecting into the Startup function) being created? Is your Configuration property being set? — mcbowes
– mcbowes, Commented Sep 14, 2017 at 17:12
public IConfiguration Configuration { get; } in the startup.cs file — Chris Lombardi
– Chris Lombardi, Commented Sep 14, 2017 at 17:22
just posted an answer, I not sure how your Configuration knows about your appSettings.json — mcbowes
– mcbowes, Commented Sep 14, 2017 at 17:24

mcbowes · Accepted Answer · 2017-09-14 17:24:16Z

1

Try changing your Startup function to

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

to instantiate your configuration and use the appsettings.json file.

answered Sep 14, 2017 at 17:24

mcbowes

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2 Comments

Chris Lombardi Over a year ago

Same error which is being thrown in ConfigureServices()

davidfowl Over a year ago

This isn't the right answer. The default config when you use the 2.0 templates.

JFT · Accepted Answer · 2017-09-14 17:15:05Z

0

The ConnectionString must be stored in the file name appsettings.json. Please try to move the Connection string part to the appsettings.json file and try. For e.g.: appsettings.json File

"Data": {
  "dbc": {
      "ConnectionString": "Server=cc;Initial Catalog=dd;Trusted_Connection=True;MultipleActiveResultSets=true"
    },
}

Startup.cs File

services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(Configuration["Data:dbc:ConnectionString"]));

answered Sep 14, 2017 at 17:15

JFT

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1 Comment

Chris Lombardi Over a year ago

My JSON is in the appsettings.json file. As a test I used your format and still received the same error.

Chris Lombardi · Accepted Answer · 2017-09-14 17:39:37Z

0

Oddly enough, moving ConnectionStrings to the top of the apsettings.json file did the trick. Thank you all for your help.

 {
      "ConnectionStrings": {
        "dbc": "Server=cc;Initial Catalog=dd;Trusted_Connection=True;MultipleActiveResultSets=true"
      },
      "Logging": {
        "IncludeScopes": false,
        "Debug": {
          "LogLevel": {
            "Default": "Warning"
          }
        },
        "Console": {
          "LogLevel": {
            "Default": "Warning"
          }
        }
      }
    }

answered Sep 14, 2017 at 17:39

Chris Lombardi

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3 Comments

mcbowes Over a year ago

did that work with your original startup code? Also, your json looks off for the Logging section which I think is why it works to move the ConnectionStrings section up.

Chris Lombardi Over a year ago

The logging section was definitely off which was the root cause. Oddly enough both variations validated using JSONlint. I fixed the syntax and now I can move the connectionstrings section around.

mcbowes Over a year ago

Yep, I guess structurally it was valid JSON, it just didn't make sense. Glad it's working for you now.

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