升级到 ASP.NET Core 2.0 后无法创建迁移

Question

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();
}

Answer 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

Answer 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'.

Answer 3

Solution 1: (Find the problem in 99% of cases)

Set Web Application project as Startup Project

Run the following commands with -verbose option.

Add-Migration Init -Verbose

-verbose option helps to actually uncover the real problem, It contains detailed errors.

Solution 2:

Rename BuildWebHost() to CreateWebHostBuilder() , because Entity Framework Core tools expect to find a CreateHostBuilder method that configures the host without running the app.

.NET Core 2.2

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

    public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .UseStartup<Startup>();
} 

.NET Core 3.1

Rename BuildWebHost() to CreateHostBuilder()

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

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });
}

Solution 3:

Make sure you added Dbcontext to dependency injection: AddDbContext<TContext> will make both your DbContext type, TContext , and the corresponding DbContextOptions<TContext> available for injection from the service container. This requires adding a constructor argument to your DbContext type that accepts DbContextOptions<TContext> .

Example: In Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<AppDbContext>(options => options.UseSqlServer(connectionString));
}

AppDbContext code:

public class AppDbContext: DbContext
{
    public AppDbContext(DbContextOptions<AppDbContext> options)
      :base(options)
    { }

}

Answer 4

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

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

Just rename BuildWebHost() to CreateWebHostBuilder() , because migrations use this method by default.

Answer 5

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.

Answer 6

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.

Answer 7

请确认您有参考

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

Answer 8

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();
}

Answer 9

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."

Answer 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);
        }
    }

Answer 11

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

Answer 12

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.

Answer 13

I was facing the 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."

This is how my problem was solved. Run the below command while you are in your solution directory

 dotnet ef migrations add InitialMigration --project "Blog.Infrastructure" --startup-project "Blog.Appication"

Here Application is my startup project containing the Startup.cs class & Infrastructure is my project containing the DbContext class.

then run update using the same structure.

dotnet ef database update --project "Blog.Infrastructure" --startup-project "Blog.Application"

Answer 14

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(); }

Answer 15

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/

Answer 16

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.

Answer 17

I ran into same problem. I have two projects in the solution. which

1. API
2. Services and repo, which hold context models

Initially, API project was set as Startup project.

I changed the Startup project to the one which holds context classes. if you are using Visual Studio you can set a project as Startup project by:

open solution explorer >> right-click on context project >> select Set as Startup project

Answer 18

First of all make sure you have configured your database in Startup.cs In my case, i was getting this error since i didn't specify the below in Startup.cs

    services.AddDbContext<ApplicationDbContext>(options =>
        options.UseSqlServer(
            Configuration.GetConnectionString("DefaultConnection"), x => x.MigrationsAssembly("<Your Project Assembly name where DBContext class resides>")));

Answer 19

Using ASP.NET Core 3.1 and EntityFrameWorkCore 3.1.0. Overriding the OnConfiguring of the context class with a parameterless constructor only

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    if (!optionsBuilder.IsConfigured)
    {
        IConfigurationRoot configuration = new ConfigurationBuilder()
           .SetBasePath(Directory.GetCurrentDirectory())
           .AddJsonFile("appsettings.json")
           .Build();
        var connectionString = configuration.GetConnectionString("LibraryConnection");
        optionsBuilder.UseSqlServer(connectionString);
    }
}

Answer 20

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

Answer 21

在主项目的 appsettings.json 文件中，我将“复制到输出目录”设置为“始终复制”并且它有效。

Answer 22

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);
        }
    }
}

Answer 23

You also can use in the startup class constructor to add json file (where the connection string lies) to the configuration. Example:

    IConfigurationRoot _config;
    public Startup(IHostingEnvironment env)
    {
        var builder = new ConfigurationBuilder()
            .SetBasePath(env.ContentRootPath)
            .AddJsonFile("appsettings.json");

        _config = builder.Build();
    }

Answer 24

For me it was because I changed the Output Type of my startup project from Console Application to Class Library .

Reverting to Console Application did the trick.

Answer 25

I had this issue in a solution that has:

• a .NET Core 2.2 MVC project
• a .NET Core 3.0 Blazor project
• The DB Context in a .NET Standard 2.0 class library project

I get the "unable to create an object..." message when the Blazor project is set as the start up project, but not if the MVC project is set as the startup project.

That puzzles me, because in the Package Manager Console (which is where I'm creating the migration) I have the Default project set to a the C# class library that actually contains the DB Context, and I'm also specifying the DB context in my call to add-migration add-migration MigrationName -context ContextName , so it seems strange that Visual Studio cares what startup project is currently set.

I'm guessing the reason is that when the Blazor project is the startup project the PMC is determining the version of .NET to be Core 3.0 from the startup project and then trying to use that to run the migrations on the .NET Standard 2.0 class library and hitting a conflict of some sort.

Whatever the cause, changing the startup project to the MVC project that targets Core 2.2, rather than the Blazor project, fixed the issue

Answer 26

For me the problem was that I was running the migration commands inside the wrong project. Running the commands inside the project that contained the Startup.cs rather than the project that contained the DbContext allowed me to move past this particular problem.

Answer 27

In my case setting the StartUp project in init helps. You can do this by executing

dotnet ef migrations add init -s ../StartUpProjectName

Answer 28

Manzur Alahi is right ! I'm trying to learn Rider by JetBrains and I had the same error when I was trying to use dotnet-ef migrations add ... in Cmd, PowerShell, etc. but when I used Visual Studio IDE I didn't have problem.

I fixed the error with:

dotnet ef migrations add InitialMigration --project "Domain.Entities" --startup-project "WebApi"

and this to update the database

dotnet ef database update --project "Domain.Entities" --startup-project "WebApi"

just like Manzur Alahi said.

Answer 29

如果上下文类在另一个类库项目中并且出现此错误，请将命令行默认项目更改为上下文项目并将解决方案启动项目设置为主API / ASP.net核心项目（您的DI容器在那里），然后重新-run 命令似乎 ef 核心工具包在https://github.com/dotnet/efcore/issues/23957和https://github.com/dotnet/efcore/issues/23853中报告了此错误

Answer 30

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