EF Core Migration error: "Unable to create an object of type 'ApplicationContext'" - asp.net-core

Question

I'm trying to do the migration with EF Core but I get an error - how can I fix this error?
PM> add-migration ini
Unable to create an object of type 'ApplicationContext'. Add an
implementation of 'IDesignTimeDbContextFactory' to
the project, or see https://go.microsoft.com/fwlink/?linkid=851728 for
additional patterns supported at design time.

Answer 1

This will also happen if you have multiple start-up projects - when migrating, just select one (in VS right click Solution and Set StartUp Projects...)

Answer 2

I had the same issue with asp.net core 3.1.
For me, it was pretty straight forward, adding an implementation of IDesignTimeDbContextFactory to the main web project fixed the issue.
A basic implementation looks something like this:
public class DesignTimeDbContextFactory : IDesignTimeDbContextFactory<YourDbContext>
{
public YourDbContext CreateDbContext(string[] args)
{
IConfigurationRoot configuration = new ConfigurationBuilder()
.SetBasePath(Directory.GetCurrentDirectory())
.AddJsonFile("appsettings.json")
.Build();
var builder = new DbContextOptionsBuilder<YourDbContext >();
var connectionString = configuration.GetConnectionString("DefaultConnection");
builder.UseSqlServer(connectionString);
return new YourDbContext(builder.Options);
}
}
Please refer to this blog post on the subject.

Answer 3

It is highly probably because of your default startup project:
Open Package manager console and write this command:
PM> Add-Migration -StartupProject[YourProjectPath(just press a tab all the.csproj paths will come up, and then choose your DataBaseLayer project to execute a migration for)] migrationName
In this way you don't need to again go to solution and set startup
project with your webProject whenever you finished adding a new migration.

Answer 4

1.Modify your code in ConfigureService with :
options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"),
x => x.MigrationsAssembly("WebApplication")));
In command line which includes WebApplication.csproj:
dotnet ef migrations add Init

Answer 5

I got this error when creating a migration. In my code in the ApplicationContext constructor, I used the Database.EnsureCreated() method. Typically this method is used for small applications where you need to check for the existence of a database and create it once. When creating an application with a database that will change with new versions and using migrations, you should not use this method.

Answer 6

In my case, this error existed because I was applying migrations at runtime. After removing Database.Migrate(); in my code, I was able to add the new migration without errors.
By the way, I used EF Core .NET command-line interface (CLI) tools, not the Package Manager Console (I run into problems I couldn't solve when I was using the Package Manager Console, so I went for the CLI alternative, and it was worth the change).
Also, make sure you use the appropriate options to select your startup project and your target project.

Answer 7

I got this error when the Primary Key for the table was not set manually (with attributes or with FluentAPI) and was not determined automatically (not "Id" kayword and not "TableName" + "Id")
Stack: ASP.NET Core EF + Postgres (Npgsql)