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How to make migrations from another project on a console application using .net6?

I am trying to execute the command add-migration with a console application which I made a context in a project apart from the console application, but when I Try to run it, it gives me the error, I am using .NET 6:
Unable to resolve service for type 'Microsoft.EntityFrameworkCore.Migrations.IMigrator'. This is often because 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<TContext> object in its constructor and passes it to the base constructor for DbContext.
Thats my context:
public class SchoolContext : DbContext
{
public DbSet<Student> Students { get; set; }
public DbSet<Course> Courses { get; set; }
public SchoolContext(DbContextOptions options) : base(options)
{
}
}
That's my main
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Persistencia;
var builder = new HostBuilder()
.ConfigureServices((hostContext, services) =>
{
services.AddLogging(configure => configure.AddConsole())
.AddDbContext<SchoolContext>(options =>
{
options.UseInMemoryDatabase( "testedb");
});
}).UseConsoleLifetime();
var host = builder.Build();
Project Structure
Project Structure

The in-memory concept in meant to simulate your database in your memory (RAM). Migrations are used to generate/update your database schema to the connected database. The in-memory database doesn't need migrations. You can directly start your application and start using your DBContext without trying to add migrations.
But
If you need to migrate with SqlServer , you can follow this tutorial.
1 - Install this package on console app
Microsoft.EntityFrameworkCore.SqlServer
2 - change your AddDbContext like *"Shop.Console" is console project name.
more connection string options.
services.AddDbContext<ShopDbContext>(options =>
{
options
.UseSqlServer("Server=[server];Database=[name]; User ID = [if have]; Password = [if have];Trusted_Connection=false;MultipleActiveResultSets=true",
sqlServerOptionsAction: o => o.MigrationsAssembly("Shop.Console"));
});
3 - open Package Manager Console and run these commands
a- dotnet ef migrations add InitialContext -p "Shop.Console"
b- dotnet ef database update -p "Shop.Console"

Can't add controller with scaffold c# .net

When I try to add new controller with scaffold visual studio prompt a error message:
There was an error running the selected code generator:
Unable to resolve service for type
1Microsoft.EntityFramework.DbContextOptions1
I have already check other question about the same problem but the answer didn't applied to my case cause already is a reference in my DbContext class to DbContext
public class HospitalDbContext : DbContext
{
public HospitalDbContext(DbContextOptions<HospitalDbContext> options)
: base(options)
{
}
public virtual DbSet<Product> Products { get; set; } = null!;
}
And Program.cs is
var builder = WebApplication.CreateBuilder(args);
builder.Configuration.AddJsonFile("appsettings.json");
builder.Services.AddControllersWithViews();
var conf = builder.Configuration;
builder.Services.AddDbContext<HospitalDbContext>(options => options.UseSqlServer(
conf.GetConnectionString("Default")
)
);
var app = builder.Build();
This is the project link on github under branch "stackoverflow": https://github.com/heitorgiacominibrasil/Hospital-Management-System-ASPNETCORE/tree/stackoverflow

I have had something similar happend once. I am not sure if this will apply to this issue but when I had this error, I just kept on pressing the "Add" button. After a couple of tries it just added the controller.
Not really sure if it will fix it but everytime I do this it works.

Solved by creating a new asp.net core mvc project, added an folder with the models/classes I needed, added the dbcontext and generated the scaffold process again. After the scaffold finished I coppied the controllers and views to my original project. This problem seems to happens when are multiple projects, and scaffold can't handle.

EF Core migration seems to ignore context option

Whilst adding Identity to my project I am doing so via a second context.
However, when running the following command
dotnet ef migrations add IdentityInitial -p .\DOH.Data -s .\DOH.API
-c AppIdentityDbContext -o DOH.Data\Identity\Migrations --verbose
I get the following output
Using assembly 'DOH.Data'.
Using startup assembly 'DOH.API'.
Using application base 'C:\Users\vic\Documents\projects\BugTracker\DOH\DOH.API\bin\Debug\netcoreapp3.1'.
Using working directory 'C:\Users\vic\Documents\projects\BugTracker\DOH\DOH.API'.
Using root namespace 'DOH.Data'.
Using project directory 'C:\Users\vic\Documents\projects\BugTracker\DOH\DOH.Data\'.
Remaining arguments: .
The Entity Framework tools version '5.0.1' is older than that of the runtime '5.0.5'. Update the tools for the latest features and bug fixes.
Finding DbContext classes...
Finding IDesignTimeDbContextFactory implementations...
Finding application service provider in assembly 'DOH.API'...
Finding Microsoft.Extensions.Hosting service provider...
Using environment 'Development'.
Using application service provider from Microsoft.Extensions.Hosting.
Found DbContext 'ApplicationContext'.
Found DbContext 'AppIdentityDbContext'.
Finding DbContext classes in the project...
Using context 'AppIdentityDbContext'.
System.InvalidOperationException: The entity type 'PersonApplicationRole' requires a primary key to be defined. If you intended to use a keyless entity type, call 'HasNoKey' in 'OnModelCreating'. For more information on keyless entity types, see https://go.microsoft.com/fwlink/?linkid=2141943.
The entity PersonApplicationRole is an existing entity that is referenced in the ApplicationContext.
This entity has already been set up in the database via a previous migration using a composite key, so I know that part works
If I change the entity definition to cope with the error just to get through the Identity migration, I end up with a migration that has all of the original entities referenced from ApplicationContext as well as the tables that need would be created as part of the Identity set up.
So this feels like the -c option is being ignored.
This is the definition of ApplicationContext:
public class DesignTimeDbContextFactory : IDesignTimeDbContextFactory<ApplicationContext>
{
public ApplicationContext CreateDbContext(string[] args)
{
IConfigurationRoot configuration = new ConfigurationBuilder()
.SetBasePath(Directory.GetCurrentDirectory())
.AddJsonFile(#Directory.GetCurrentDirectory() + "/../DOH.API/appsettings.Development.json").Build();
var builder = new DbContextOptionsBuilder<ApplicationContext>();
var connectionString = configuration.GetConnectionString("doh.dev");
builder.UseNpgsql(connectionString);
return new ApplicationContext(builder.Options);
}
}
public class ApplicationContext : DbContext
{
public ApplicationContext(DbContextOptions<ApplicationContext> options) : base(options)
{ }
}
This is the current AppIdentityDbContext:
public class AppIdentityDbContext : IdentityDbContext<AppUser>
{
public AppIdentityDbContext(DbContextOptions<AppIdentityDbContext> options) : base(options)
{
}
protected override void OnModelCreating(ModelBuilder builder)
{
base.OnModelCreating(builder);
}
}
These are the two connection strings
"ConnectionStrings": {
"doh.dev": "Host=x.x.x.x;Port=5432;Username=dohdbsvc;Password=******;Database=dohdb;",
"doh.dev.identity": "Host=x.x.x.x;Port=5432;Username=dohdbsvc;Password=******;Database=doh.identitydb;"
},
And here are the two contexts as included in my startup
services.AddDbContext<ApplicationContext>(options =>
{
options.EnableDetailedErrors();
options.UseNpgsql(
Configuration.GetConnectionString("doh.dev"));
});
services.AddDbContext<AppIdentityDbContext>(options =>
{
options.EnableDetailedErrors();
options.UseNpgsql(
Configuration.GetConnectionString("doh.dev.identity"));
});
For reference, this is a .net core 3.1 project using the following packages
Microsoft.AspNetCore.Identity.EntityFrameworkCore 5.0.5
Microsoft.AspNetCore.Identity 2.2.0
Microsoft.EntityFrameworkCore 5.0.5
Microsoft.EntityFrameworkCore.Design 5.0.5
Npgsql.EntityFrameworkCore.PostgreSQL 5.0.2
Microsoft.EntityFrameworkCore.Tools 5.0.5
I have been through the docs and countless examples others have posted on various blogs and forums and I appear to be following recommended practice, so if anyone can see why this is happening, please share your thoughts.

dotnet core database first using NetTopologySuite

I recently upgraded to the newest version of EntityFrameworkCore.PostgreSQL but the spacial data didn't seem to work, because they now use NetTopologySuite see here
To set up the NetTopologySuite plugin, add the
Npgsql.EntityFrameworkCore.PostgreSQL.NetTopologySuite nuget to your
project. Then, make the following modification to your UseNpgsql()
line:
I use the dotnet ef dbcontext scaffold command
dotnet ef dbcontext scaffold "MyConnectionString" Npgsql.EntityFrameworkCore.PostgreSQL
however, the scaffold command doesn't seem to use the NetTopologySuite mapping. I still get the following error
Could not find type mapping for column 'public.behaviour.coord' with data type 'geometry(Point)'. Skipping column.
How can I scaffold my database using NetTopologySuite

I had a similar problem, after updating the postgre library, I had to delete migration files and regenerate new ones

public class EFDesignTimeService : IDesignTimeServices
{
public void ConfigureDesignTimeServices(IServiceCollection services)
{
new EntityFrameworkRelationalServicesBuilder(services).TryAddProviderSpecificServices(x =>
{
x.TryAddSingleton<INpgsqlOptions, NpgsqlOptions>(p =>
{
var dbOption = new DbContextOptionsBuilder()
.UseNpgsql("connection string",
ob => ob.UseNodaTime().UseNetTopologySuite()).Options;
var npgOptions = new NpgsqlOptions();
npgOptions.Initialize(dbOption);
return npgOptions;
});
});
}
}

I was using the geometry(Point, 4326) type
and I had to change the type to geometry
ALTER COLUMN coord TYPE geometry;

Unable to create migrations after upgrading to ASP.NET Core 2.0

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();
}

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

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'.

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)
{ }
}

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.

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.

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.

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();
}

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://learn.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."

Please verify that you have the reference
<PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="2.0.0" />

From
https://learn.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);
}
}

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

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.

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"

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();
}

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/

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.

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

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>")));

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);
}
}

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

In main project's appsettings.json file, I had set 'Copy to Output directory' to "Copy always" and it worked.

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);
}
}
}

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();
}

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.

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

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.

In my case setting the StartUp project in init helps. You can do this by executing
dotnet ef migrations add init -s ../StartUpProjectName

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.

If context class is in another class library project and this error is occurred, change command line default project to the context project and set solution startup project to the main API / ASP.net core project (that your DI container is there), then re-run command
It seems ef core tools package has this bug a reported in
https://github.com/dotnet/efcore/issues/23957 and https://github.com/dotnet/efcore/issues/23853

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