.NET 6 - WebAPI with EFCore - error generating migrations

Question

To demonstrate this issue I've created a small project using the webapi template in .NET 6.

The issue when trying to add my first migration, I get the following error (running with the verbose option);

No static method 'CreateHostBuilder(string[])' was found on class 'Program'. No application service provider was found. Finding DbContext classes in the project... Found DbContext 'BloggingContext'. Microsoft.EntityFrameworkCore.Design.OperationException: Unable to create an object of type 'BloggingContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728

As the new .NET 6 template does not have CreateHostBuilder in the startup, the EF tools are trying to create an instance of the context class, but because I'm using DI in the constructor to obtain the configuration this error arises.

My demo project;

  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="5.0.11">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="5.0.11" />
    <PackageReference Include="Swashbuckle.AspNetCore" Version="6.1.5" />
  </ItemGroup>

</Project>

Created a models class to hold the db context and entities.

using Microsoft.EntityFrameworkCore;

namespace dotnet6apiefcore;

public class BloggingContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }
    public IConfiguration _configuration { get; }
    public BloggingContext(IConfiguration configuration)
    {
        this._configuration = configuration;
    }
    protected override void OnConfiguring(DbContextOptionsBuilder options) {
        var connectString = _configuration.GetValue<string>("ConnectionString");
        options.UseSqlServer(connectString);
    }        
}

public class Blog
{
    public int BlogId { get; set; }
    public string Url { get; set; }

}

In the program.cs I register the BloggingContext.

using dotnet6apiefcore;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.

builder.Services.AddControllers();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddDbContext<BloggingContext>();
var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

app.Run();

Answer 1

I was running into a similar error and just was able to successfully complete my migrations.

Verify the NuGet packages for all your projects are using the same version, and since you're using .NET 6, you need to update your EF Core packages to the latest pre-release.

In the NuGet Package Manager for your projects go to the 'Updates' tab and make sure to select 'Include prerelease'. This should show some results that you're able to update to.

Once I did this, I was able to run my same migrations command and successfully complete migrations.

NOTE: This will only be accurate until the Production Release of .NET 6. After .NET 6 is released, you will need to make sure your packages are running the current release (or the corresponding version with your projects and ef core dotnet tools).