Error while Add-Migration ef core 2 preview 1

Question

I'm trying to do a sample on ef core 2 but I'm getting the following when I try to add migrations

PM> Add-Migration InitialCreate
No parameterless constructor was found on 'ToDoContext'. Either add a parameterless constructor to 'ToDoContext' or add an implementation of 'IDbContextFactory<ToDoContext>' in the same assembly as 'ToDoContext'.

I followed this tutorial https://learn.microsoft.com/en-us/ef/core/get-started/aspnetcore/new-db Here is my code.

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        var connection = @"Server=(localdb)\mssqllocaldb;Database=EFGetStarted.AspNetCore.NewDb;Trusted_Connection=True;";
        services.AddDbContext<ToDoContext>(options => options.UseSqlServer(connection));
        services.AddMvc();
    }
}

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

    }
    public DbSet<ToDo> ToDos { get; set; }
}

public class ToDo
{
    public int Id { get; set; }
    public string Title { get; set; }
    public bool Completed { get; set; }
}

bricelam · Accepted Answer · 2017-06-22T15:31:35.527

2

I recommend implementing IDbContextFactory. Here is an example.

class ToDoContextFactory : IDbContextFactory<ToDoContext>
{
    public ToDoContext Create(DbContextFactoryOptions options)
    {
        var serviceCollection = new ServiceCollection()
            .AddLogging();
        new Startup().ConfigureServices(serviceCollection);

        var serviceProvider = serviceCollection.BuildServiceProvider();

        return serviceProvider.GetRequiredService<ToDoContext>();
    }
}

In 2.0, the ASP.NET Core team updated the recommended pattern for building apps. This broke the way the EF Core tools accessed the application's service provider. This lead us to remove the way we invoked Startup.ConfigureService and update it to invoke Program.BuildWebHost instead. This means that any apps upgrading from 1.x to 2.0 will either need to update to the new pattern or implement IDbContextFactory before they can use the 2.0 tools.

edited Jun 22 '17 at 15:31

answered Jun 21 '17 at 15:48

bricelam

28,825
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Thanks Its working. Can you please provide any link or explanation – mahindar Jun 21 '17 at 18:12
No docs yet, but here's a year-old issue to write some :-) https://github.com/aspnet/EntityFramework.Docs/issues/204 – bricelam Jun 22 '17 at 15:26
(Added some explanation to the answer.) – bricelam Jun 22 '17 at 15:31

Steve · Answer 2 · 2017-06-20T18:20:29.057

0

change the TDoContext class constructor to:

public ToDoContext()
    : base("PUT_WEB_CONFIG_CONNECTION_STRING_NAME_HERE")
{

}

Where PUT_WEB_CONFIG_CONNECTION_STRING_NAME_HERE, is the name part in your web.config of your conection string, that portion of your web.config shold like something like:

 <connectionStrings>
    <add name="DefaultConnection" ... />
  </connectionStrings>

so you would use "DefaultConnection"

edited Jun 20 '17 at 18:20

answered Jun 20 '17 at 18:18

Steve

502
3
12

EF Core does not have a constructor that supports a string parameter – Camilo Terevinto Jun 20 '17 at 18:19
yep, sorry, I missed "core", so ill take your word for it – Steve Jun 20 '17 at 18:21

score 0 · Answer 3 · answered Jun 20 '17 at 18:20

0

Well, the problem is very clear:

No parameterless constructor was found

So, you need this:

public class ToDoContext : DbContext
{

    public ToDoContext() // this is a parameterless (with no parameters) constructor 
    { }

    public ToDoContext(DbContextOptions<ToDoContext> options) : base(options)
    { }

    public DbSet<ToDo> ToDos { get; set; }
}

answered Jun 20 '17 at 18:20

Camilo Terevinto

31,141
6
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Adding parameter less constructor giving a new error `System.InvalidOperationException: No database provider has been configured for this DbContext. A provider can be configured by overriding the DbContext.OnConfiguring method or by using AddDbContext on the application service provider. If AddDbContext is used, then also ensure that your DbContext type accepts a DbContextOptions object in its constructor and passes it to the base constructor for DbContext. at Microsoft.EntityFrameworkCore.Internal.DbContextServices` ` – mahindar Jun 21 '17 at 18:17

Error while Add-Migration ef core 2 preview 1

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