"Parameter count mismatch" error during adding Entity Framework migration under .NET Core 2.0

Question

After migration of my project to .NET Core 2.0, fresh install of Visual Studio 15.5 and .NET CORE sdk 2.1.2, I am having an error when trying to add a migration using EF Core.

C:\Projects\SQLwallet\SQLwallet>dotnet ef migrations add IdentityServer.
An error occurred while calling method 'BuildWebHost' on class 'Program'.
Continuing without the application service provider. Error: Parameter count mismatch.


Done. To undo this action, use 'ef migrations remove'

As a result an empty migration class is created, with empty Up() and Down() methods.

The program.cs looks like:

public class Program
{

    public static IWebHost BuildWebHost(string[] args, string environmentName)
    {...}

    public static void Main(string[] args)
    {


        IWebHost host;
        host = BuildWebHost(args, "Development");

Please advise. The migration worked fine while on Core 1.0. I have a IDesignTimeDbContextFactory implemented, and my DBContext class has a parameterless constructor, so it could not be the reason.

You can safely ignore the message. It will go away when issue #9076 is resolved. — bricelam
– bricelam, Commented Dec 8, 2017 at 0:10
The problem is that the migration is not generating properly, it is empty. — Glebby
– Glebby, Commented Dec 8, 2017 at 7:50

ddagsan · Accepted Answer · 2019-05-21 10:51:45Z

10

My solution is to pass Array to HasData function, not generic List. If you use List, try to convert array with ToArray function.

Here is an example:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
      var users = new List<User>();
      var user1 = new User() { Id = 1, Username = "user_1" };
      var user2 = new User() { Id = 2, Username = "user_2" };

      users = new List<User>() { user1, user2 };
      modelBuilder.Entity<User>().HasData(users.ToArray());
}

edited May 21, 2019 at 10:51

answered Nov 20, 2018 at 6:06

ddagsan

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1 Comment

Tohid Over a year ago

It worked for me, thank you. Any idea why it doesn't work with generic lists?

Connell.O'Donnell · Accepted Answer · 2018-09-27 11:49:26Z

2

Take a look at the OnModelCreating method in your DbContext. Make sure it calls base.OnModelCreating(builder). It should look something like:

protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);            

        builder.Entity<T>().HasData(...);
    }

If you are using builder.Entity<T>().HasData(...) to seed your data, make sure you pass it a T[] and not an IEnumerable.

answered Sep 27, 2018 at 11:49

Connell.O'Donnell

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1 Comment

JuanK Over a year ago

Very helpful: "If you are using builder.Entity<T>().HasData(...) to seed your data, make sure you pass it a T[] and not an IEnumerable"

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