Myujth

In the AppContext.cs besides AppContext class add another class:

// required when local database deleted
public class ToDoContextFactory : IDesignTimeDbContextFactory<AppContext>

 public AppContext CreateDbContext(string args)
 
 var builder = new DbContextOptionsBuilder<AppContext>();
 builder.UseSqlServer("Server=localhost;Database=DbName;Trusted_Connection=True;MultipleActiveResultSets=true");
 return new AppContext(builder.Options);
 

This will solve your second problem:

"Unable to create an object of type 'MyContext'. Add an implementation of 'IDesignTimeDbContextFactory' to the project,

After that you will be able to add-migration Initial and execute it by running update-database command.
However if running these commands when there is no DataBase yet in your local SqlServer you will get the warning like your first error: "An error

occurred while calling method 'BuildWebHost' on class 'Program'... The
login failed. Login failed for user '...'"

But it is not error because migration will be created and it can be executed.
So just ignore this error for the first time, and latter since Db will exist it won't happen again.

No need for IDesignTimeDbContextFactory.

Run

add-migration initial -verbose

that will reveal the details under

An error occurred while accessing the IWebHost on class 'Program'. Continuing without the application service provider.

warning, which is the root cause of the problem.

In my case, problem was, having ApplicationRole : IdentityRole<int> and invoking services.AddIdentity<ApplicationUser, IdentityRole>() which was causing below error

System.ArgumentException: GenericArguments[1], 'Microsoft.AspNetCore.Identity.IdentityRole', 
on 'Microsoft.AspNetCore.Identity.EntityFrameworkCore.UserStore`9[TUser,TRole,TContext,
TKey,TUserClaim,TUserRole,TUserLogin,TUserToken,TRoleClaim]' violates the constraint of type 'TRole'.
---> System.TypeLoadException: GenericArguments[1], 'Microsoft.AspNetCore.Identity.IdentityRole', 
on 'Microsoft.AspNetCore.Identity.UserStoreBase`8[TUser,TRole,TKey,TUserClaim,
TUserRole,TUserLogin,TUserToken,TRoleClaim]' violates the constraint of type parameter 'TRole'.

please verify that you have the reference

<PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="2.0.0" />

You can try this solution from this discussion, which was inspired by this post.

public static IWebHost MigrateDatabase(this IWebHost webHost)

 using (var scope = webHost.Services.CreateScope())
 
 var services = scope.ServiceProvider;

 try
 
 var db = services.GetRequiredService<MyContext>();
 db.Database.Migrate();
 
 catch (Exception ex)
 
 var logger = services.GetRequiredService<ILogger<Program>>();
 logger.LogError(ex, "An error occurred while migrating the database.");
 
 

 return webHost;

public static void Main(string args)

 BuildWebHost(args)
 .MigrateDatabase()
 .Run();

Something that really helped me was this article: https://elanderson.net/2017/09/unable-to-create-an-object-of-type-applicationdbcontext-add-an-implementation-of-idesigntimedbcontextfactory/

The basic idea is that in the change over from .net core 1 to 2 all db initialization should be moved out of the StartUp.cs and into the Program.cs. Otherwise the EF tasks try and run your DB inits when doing tasks.

"There is a nice section in the official migration docs (https://docs.microsoft.com/en-us/ef/core/miscellaneous/1x-2x-upgrade) titled “Move database initialization code” which I seemed to have missed. So before you head down any rabbit holes like I did make sure this isn’t what is causing your need to add an implementation of IdesignTimeDbContextFactory."

In my case, the cause of the problem was multiple startup projects. I have three projects in my solution: Mvc, Api, and Dal. DbContext and Migrations in the Dal project.

I had configured multiple startup projects. Both Mvc and Api projects were running when I clicked Start. But in this case I was getting this error.

"Unable to create an object of type 'MyContext'. Add an implementation
of 'IDesignTimeDbContextFactory' to the project, or see
https://go.microsoft.com/fwlink/?linkid=851728 for additional patterns
supported at design time."

I could successfully add migration after setting Mvc as the only startup project and selecting Dal in the Package Manager Console.

There's a problem with ef seeding db from Startup.Configure in 2.0 ... you can still do it with this work around. Tested and worked fine

https://garywoodfine.com/how-to-seed-your-ef-core-database/

In my case I got the problem because I had a method named SeedData.EnsurePopulated() being called on my Startup.cs file.

public class Startup

 public Startup(IConfiguration configuration) => Configuration = configuration;
 public IConfiguration Configuration get; 

 public void ConfigureServices(IServiceCollection services)
 
 //
 

 public void Configure(IApplicationBuilder app, IHostingEnvironment env)
 
 app.UseDeveloperExceptionPage();
 app.UseStatusCodePages();
 app.UseStaticFiles();
 app.UseSession();
 app.UseMvc(routes =>
 
 //
 );

 SeedData.EnsurePopulated(app);
 

The work of SeedData class is to add initial data to the database table. It's code is:

public static void EnsurePopulated(IApplicationBuilder app)
 
 ApplicationDbContext context = app.ApplicationServices.GetRequiredService<ApplicationDbContext>();
 context.Database.Migrate();
 if (!context.Products.Any())
 
 context.Products.AddRange(
 new Product
 
 Name = "Kayak",
 Description = "A boat for one person",
 Category = "Watersports",
 Price = 275
 ,
 ....
 );
 context.SaveChanges();
 
 

SOLUTION

Before doing migration simply comment out the calling of SeedData class in the Startup.cs file.

// SeedData.EnsurePopulated(app);

That solved my problem and hope your problem is also solved in the same way.

From

https://docs.microsoft.com/en-us/ef/core/miscellaneous/cli/dbcontext-creation

When you create a new ASP.NET Core 2.0 application, this hook is
included by default. In previous versions of EF Core and ASP.NET Core,
the tools try to invoke Startup.ConfigureServices directly in order to
obtain the application's service provider, but this pattern no longer
works correctly in ASP.NET Core 2.0 applications. If you are upgrading
an ASP.NET Core 1.x application to 2.0, you can modify your Program
class to follow the new pattern.

Add Factory in .Net Core 2.x

public class BloggingContextFactory : IDesignTimeDbContextFactory<BloggingContext>
 
 public BloggingContext CreateDbContext(string args)
 
 var optionsBuilder = new DbContextOptionsBuilder<BloggingContext>();
 optionsBuilder.UseSqlite("Data Source=blog.db");

 return new BloggingContext(optionsBuilder.Options);
 
 

Previously, you configured the seed data in the Configure method in Startup.cs. It is now recommended that you use the Configure method only to set up the request pipeline. Application startup code belongs in the Main method.

The refactored Main method. Add the following references to the Program.cs:

using Microsoft.Extensions.DependencyInjection;

using MyProject.MyDbContextFolder;

public static void Main(string args)

 var host = BuildWebHost(args);

 using (var scope = host.Services.CreateScope())
 
 var services = scope.ServiceProvider;
 try
 
 var context = services.GetRequiredService<MyDbConext>();
 DbInitializer.Initialize(context);
 
 catch (Exception ex)
 
 var logger = services.GetRequiredService<ILogger<Program>>();
 logger.LogError(ex, "An error occurred while seeding the database.");
 
 

 host.Run();

A better solution :

If your startup project is an ASP.NET Core app, the tools try to obtain the DbContext object from the application's service provider.

The tool first try to obtain the service provider by invoking Program.BuildWebHost() and accessing the IWebHost.Services property.

add this method after Main Method in Program.cs

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

I got the same issue since I was referring old- Microsoft.EntityFrameworkCore.Tools.DotNet

<DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" Version="1.0.0" />

After upgrading to the newer version it got resolved

In main project's appsettings.json file, I had set 'Copy to Output directory' to "Copy always" and it worked.

Sample DB context class for .net core console applications

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Design;
using Microsoft.Extensions.Configuration;
using System.IO;

namespace EmailServerConsole.Data

 public class EmailDBContext : DbContext
 
 public EmailDBContext(DbContextOptions<EmailDBContext> options) : base(options) 
 public DbSet<EmailQueue> EmailsQueue get; set; 
 

 public class ApplicationContextDbFactory : IDesignTimeDbContextFactory<EmailDBContext>
 
 EmailDBContext IDesignTimeDbContextFactory<EmailDBContext>.CreateDbContext(string args)
 
 IConfigurationRoot configuration = new ConfigurationBuilder()
 .SetBasePath(Directory.GetCurrentDirectory())
 .AddJsonFile("appsettings.json")
 .Build();
 var builder = new DbContextOptionsBuilder<EmailDBContext>();
 var connectionString = configuration.GetConnectionString("connection_string");
 builder.UseSqlServer(connectionString);
 return new EmailDBContext(builder.Options);
 
 

I had this problem and this solved By Set -> Web Application(Included Program.cs) Project to -> "Set as Startup Project"

Then run -> add-migration initial -verbose

in Package Manager Console

Set as Startup Project

In my case this error occurred due to I remove MyDbContext from ConfigureServices because of some Design Patterns. Check that. In Startup.cs => ConfigureServices add these lines:

var connectionString = "Application Connection String!!!";
services.AddDbContext<MyDbContext>(c => c.UseSqlServer(connectionString));