Throw better exception when app might be using old ASP.NET pattern

[shawnwildermuth]

Describe what is not working as expected.

I expected that the startup registration would allow me to use the EF Tools without implementing a IDbConnectionFactory. I do not have an empty constructor on my context class, but by isn't the tooling using DI to create an instance? Here is my DbContext class:

  public class VacationContext : DbContext
  {
    private IConfiguration _config;

    public VacationContext(IConfiguration config, DbContextOptions builder): base(builder)
    {
      _config = config;
    }

    public DbSet<VacationRequest> VacationRequests { get; set; }
    public DbSet<Employee> Employees { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
      base.OnConfiguring(optionsBuilder);

      optionsBuilder.UseSqlServer(_config["Data:MainConnection"]);
    }
  }

If you are seeing an exception, include the full exceptions details (message and stack trace).

d:\courses\PS\aspnetcore2\Examples\Exemplar\VacationPicker>dotnet ef database drop

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:05.15
No parameterless constructor was found on 'VacationContext'. Either add a parameterless constructor to 'VacationContext' or add an implementation of 'IDbContextFactory<VacationContext>' in the same assembly as 'VacationContext'.

Steps to reproduce

Include a complete code listing (or project/solution) that we can run to reproduce the issue.

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<code listing>

Further technical details

EF Core version: (found in .csproj file)

 <PackageReference Include="Microsoft.AspNetCore.All" Version="2.0.0-preview1-final" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="2.0.0-preview1-final" />
    <DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" Version="2.0.0-preview1-final" />

Database Provider: Microsoft.EntityFrameworkCore.SqlServer Operating system: Win10 IDE: VS2017 Preview 1

[bricelam]

Dupe of #8164. This will be fixed in 2.0.0-preview2-final.

[ajcvickers]

ASP.NET Core changed the default pattern for applications in 2.0. Instead of having a ConfigureServices call, there is now a Main method with a BuildWebHost method split out. It was explicitly stated by @DamianEdwards that EF does not need to try to keep supporting the old pattern and instead old applications should:

• Update their code to the new pattern
• or implement an IDbContextFactory

However, our exception message only suggests the latter, which means that people will not be aware that updating their app to the new pattern is a solution. We should update the message with a fwlink (@divega) to documentation on how to update 1.x ASP.NET Core app to the 2.0 pattern.

[divega]

I have created https://go.microsoft.com/fwlink/?linkid=851728. Currently it points to one of the ASP.NET Core walkthroughs, but we should update it as part of https://github.com/aspnet/EntityFramework.Docs/issues/409.

[shawnwildermuth]

I don't quite get this, does this mean that for separate data projects, we no longer need a startup class to support EF Tooling? Instead we should do what in Main to support it without needing to implement the IDbContextFactory? I'm seeing this is a new 2.0 project, not a converted 1.x project.

This is the program.cs:

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

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

[divega]

@shawnwildermuth AFAIR, in 2.0-preview1 we were in an intermediary state in which we didn't support the Program.BuildWebHost method so you had to have an IDbContextFactory. The change to support Program.BuildWebHost is in preview2.