Unable to create migrations after upgrading to ASP

问题:

After upgrading to ASP.NET Core 2.0, I can't seem to create migrations anymore.

I'm getting

"An error occurred while calling method 'BuildWebHost' on class 'Program'. Continuing without the application service provider. Error: One or more errors occurred. (Cannot open database "..." requested by the login. The login failed. Login failed for user '...'"

and

"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."

The command I previously ran was $ dotnet ef migrations add InitialCreate --startup-project "..\Web" (from the project/folder with the DBContext).

Connection string: "Server=(localdb)\\mssqllocaldb;Database=database;Trusted_Connection=True;MultipleActiveResultSets=true"

This is 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();
}

回答1:

You can add a class that implements IDesignTimeDbContextFactory inside of your Web project.

Here is the sample code:

public class DesignTimeDbContextFactory : IDesignTimeDbContextFactory<CodingBlastDbContext>
{
    public CodingBlastDbContext CreateDbContext(string[] args)
    {
        IConfigurationRoot configuration = new ConfigurationBuilder()
            .SetBasePath(Directory.GetCurrentDirectory())
            .AddJsonFile("appsettings.json")
            .Build();
        var builder = new DbContextOptionsBuilder<CodingBlastDbContext>();
        var connectionString = configuration.GetConnectionString("DefaultConnection");
        builder.UseSqlServer(connectionString);
        return new CodingBlastDbContext(builder.Options);
    }
}

Then, navigate to your Database project and run the following from command line:

dotnet ef migrations add InitialMigration -s ../Web/

dotnet ef database update -s ../Web/

-s stands for startup project and ../Web/ is the location of my web/startup project.

resource

回答2:

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'.

回答3:

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.

回答4:

please verify that you have the reference

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

回答5:

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();
}

回答6:

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."

回答7:

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.

回答8:

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/

回答9:

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.

回答10:

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);
        }
    }

回答11:

If you want to avoid those IDesignTimeDbContextFactory thing: Just make sure that you don't use any Seed method in your startup. I was using a static seed method in my startup and it was causing this error for me.

回答12:

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();
}

回答13:

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();

回答14:

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

回答15:

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

回答16:

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

回答17:

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);
        }
    }
}

回答18:

I had same problem. Just changed the ap.jason to application.jason and it fixed the issue

回答19:

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));