Reputation: 1295

Unable to create an object of type 'DbContext'

When I try to run

dotnet ef migration add Init

I get error

Unable to create an object of type 'IdentityContext'.

I know what caused the problem. I wanted to learn using message bus and added it to my project, so I run for some course and implemented it. Ofc bus working perfectly. But the problem is that I can no longer migrate via EF.

My Startup.cs before was.

public class Program
{
    public static void Main(string[] args)
    {
        CreateWebHostBuilder(args).Build().Run();
    }

    public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .UseStartup<Startup>();
}

Now it looks like this.

public static void Main(string[] args)
{
  ServiceHost.Create<Startup>(args)
    .UseRabbitMq()
    .Build()
    .Run();
}

And ServiceHost class

public void Run() => _webHost.Run();

public static HostBuilder Create<TStartup>(string[] args) where TStartup : class
{
  Console.Title = typeof(TStartup).Namespace;
  var config = new ConfigurationBuilder()
    .AddEnvironmentVariables()
    .AddCommandLine(args)
    .Build();
  var webHostBuilder = WebHost.CreateDefaultBuilder()
    .UseConfiguration(config)
    .UseStartup<TStartup>();

  return new HostBuilder(webHostBuilder.Build());
}

So anyone would give advice why migration stopped to work? For me it looks like it should work, but it isn't so I guess I'm wrong.

And ofc I have in my Startup.cs

services.AddEntityFrameworkNpgsql().AddDbContext<IdentityContext>(options =>
    options.UseNpgsql(Configuration.GetConnectionString("IdentityConnection")));

EDIT IdentityContext class:

  public class IdentityContext : DbContext
  {
    public IdentityContext(DbContextOptions<IdentityContext> options) : base(options)
    {
      while (!Debugger.IsAttached)
      {
        Thread.Sleep(100);
      }
    }
    public DbSet<User> Users { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
      modelBuilder.Entity<User>().HasIndex(user => user.Email).IsUnique();
      modelBuilder.Entity<User>().HasIndex(user => user.Username).IsUnique();
    }
  }

EDIT2. Verbose migration

Using project '/home/msek/Projects/inz/CrossX/src/CrossX.Identity/CrossX.Identity.csproj'.
Using startup project '/home/msek/Projects/inz/CrossX/src/CrossX.Identity/CrossX.Identity.csproj'.
Writing '/home/msek/Projects/inz/CrossX/src/CrossX.Identity/obj/CrossX.Identity.csproj.EntityFrameworkCore.targets'...
dotnet msbuild /target:GetEFProjectMetadata /property:EFProjectMetadataFile=/tmp/tmpCq3PQa.tmp /verbosity:quiet /nologo /home/msek/Projects/inz/CrossX/src/CrossX.Identity/CrossX.Identity.csproj
Writing '/home/msek/Projects/inz/CrossX/src/CrossX.Identity/obj/CrossX.Identity.csproj.EntityFrameworkCore.targets'...
dotnet msbuild /target:GetEFProjectMetadata /property:EFProjectMetadataFile=/tmp/tmpR48yu8.tmp /verbosity:quiet /nologo /home/msek/Projects/inz/CrossX/src/CrossX.Identity/CrossX.Identity.csproj
dotnet build /home/msek/Projects/inz/CrossX/src/CrossX.Identity/CrossX.Identity.csproj /verbosity:quiet /nologo

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

Time Elapsed 00:00:01.17
dotnet exec --depsfile /home/msek/Projects/inz/CrossX/src/CrossX.Identity/bin/Debug/netcoreapp2.2/CrossX.Identity.deps.json --additionalprobingpath /home/msek/.nuget/packages --runtimeconfig /home/msek/Projects/inz/CrossX/src/CrossX.Identity/bin/Debug/netcoreapp2.2/CrossX.Identity.runtimeconfig.json /home/msek/.dotnet/tools/.store/dotnet-ef/2.2.2/dotnet-ef/2.2.2/tools/netcoreapp2.2/any/tools/netcoreapp2.0/any/ef.dll migrations add Init --assembly /home/msek/Projects/inz/CrossX/src/CrossX.Identity/bin/Debug/netcoreapp2.2/CrossX.Identity.dll --startup-assembly /home/msek/Projects/inz/CrossX/src/CrossX.Identity/bin/Debug/netcoreapp2.2/CrossX.Identity.dll --project-dir /home/msek/Projects/inz/CrossX/src/CrossX.Identity/ --language C# --working-dir /home/msek/Projects/inz/CrossX/src/CrossX.Identity --verbose --root-namespace CrossX.Identity
Using assembly 'CrossX.Identity'.
Using startup assembly 'CrossX.Identity'.
Using application base '/home/msek/Projects/inz/CrossX/src/CrossX.Identity/bin/Debug/netcoreapp2.2'.
Using working directory '/home/msek/Projects/inz/CrossX/src/CrossX.Identity'.
Using root namespace 'CrossX.Identity'.
Using project directory '/home/msek/Projects/inz/CrossX/src/CrossX.Identity/'.
Finding DbContext classes...
Finding IDesignTimeDbContextFactory implementations...
Finding application service provider...
Finding IWebHost accessor...
No CreateWebHostBuilder(string[]) method was found on type 'CrossX.Identity.Program'.
No application service provider was found.
Finding DbContext classes in the project...
Found DbContext 'IdentityContext'.
Microsoft.EntityFrameworkCore.Design.OperationException: Unable to create an object of type 'IdentityContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728 ---> System.MissingMethodException: No parameterless constructor defined for this object.
   at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean wrapExceptions, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor)
   at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean wrapExceptions, Boolean skipCheckThis, Boolean fillCache)
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass12_3.<FindContextTypes>b__13()
   --- End of inner exception stack trace ---
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass12_3.<FindContextTypes>b__13()
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(Func`1 factory)
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(String contextType)
   at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
Unable to create an object of type 'IdentityContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728

Upvotes: 80

Answers (25)

KamilStachera

Reputation: 21

For anyone whos having this issue as .net 9.0 came out: If you are using postgresSql (version 8.0.10) make sure that you don't upgrade EF Core to 9.0, If you update to 9.0 you can get this error:

The exception 'Cannot resolve scoped service 'System.Collections.Generic.IEnumerable`1[Microsoft.EntityFrameworkCore.Infrastructure.IDbContextOptionsConfiguration`1[DbContext]]' from root provider.' was thrown while attempting to find 'DbContext' types. For the different patterns supported at design time

To downgrade EF Core version simply run (from 9.x to 8.x):

dotnet add package Microsoft.EntityFrameworkCore --version 8.0.10

Upvotes: 1

sorin alexandru

Reputation: 1

Make sure that YourContext_DbContext is Concrete: Change YourContext_DbContext from an abstract class to a concrete class. You need to remove the abstract keyword and ensure it has a valid constructor. It worked for me to connect to postgress.

using Microsoft.EntityFrameworkCore;

namespace **YourNamespace**
{
    public class **YourContext**_DbContext : DbContext 
    //public ***abstract*** class **YourContext**_DbContext : DbContext - **not OK** ,delete **abstract** if it exists by mystake.
    {
        public **YourContext**_DbContext(DbContextOptions<**YourContext**_DbContext> options) : base(options)
        {
        }

        public virtual DbSet<**YourModelClass**> **YourModelClas**{ get; set; }
       //insert all your model classes.

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
            // Add any model configurations here
        }

        public static void InitialSeedDatabase(ModelBuilder modelBuilder)
        {
            // Seed data if needed
        }
    }
}

Upvotes: 0

Dib

Reputation: 2083

Also check that your appsettings.json or appsettings.<environmnet>.json does not have a corrupted structure. We spotted a build had failed due to this error. It turned out to be a missing comma in the staging environment appsettings file. We clearly need to "lint" our .json files going forward!

Upvotes: 0

pekaaw

Reputation: 2597

Even with a IDesignTimeDbContextFactory implementation you might run into problems with dotnet ef migration add. If you use Visual Studio, using Add-Migration instead might solve your problem.

I got this error when I used the Package Manager Console in VS2022:

PM> dotnet ef migrations add MigrationName --project .\DataAccess\DataAccess.csproj --startup-project .\DataAccess\DataAccess.csproj
Build started...
Build succeeded.
Unable to create a 'DbContext' of type 'AppDbContext'. The exception 'Object reference not set to an instance of an object.' was thrown while attempting to create an instance. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728
PM>

My setup:

Visual Studio 2022
dotnet-ef v8.0.7 (installed with dotnet tool install --global dotnet-ef
Project DataAccess that implements repositories defined in the business layer
DataAccess.AppDbContext that implements DbContext
DataAccess.AppDbContextFactory that implements IDesignTimeDbContextFactory<AppDbContext>

I'm not sure why the CLI command fails, but Add-Migration from Package Manager Console in Visual Studio worked.

Upvotes: 0

z zandi

Reputation: 21

I wrote this command in Package Manager Console and the problem was solved

dotnet-ef migrations add migrationName --context DBContext --project=MyProject.Data --startup-project=MyProject.Web -o Persistence\Migrations

'migrationName' is your migration name.
'MyProject.Data' is the layer that DBContext is in it.
'MyProject.Web' is your web project.

Upvotes: 0

ORION

Reputation: 2401

This can be caused by not being signed into your Microsoft account in Visual Studio. I've seen it many times. As soon as you re-enter your credentials, EF migrations will work fine. Also, make sure your startup project is set correctly.

Upvotes: 0

Rasitha Gamage

Reputation: 61

I was having the same error. but I was trying to do different operation. posting my experience hoping it will help someone.

initially got

dotnet ef migrations bundle
Build started...
Build succeeded.
Unable to create an object of type 'Di2Context'. For the different patterns `supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728`

then I ran dotnet ef migrations bundle --verbose to see fully detailed error.

In my solution there were several projects like Api, Domain, Infrastructure, Persistent etc.I was running this command inside Persistant project because it has the migration.cs files.

When I moved inside Api project (which was my startup project) and ran

dotnet ef migrations bundle --self-contained -r linux-x64

created the migration efbundle.exe without problem.

Upvotes: 1

greenoldman

Reputation: 21052

Another check is to make sure the program runs in the first place. For unknown reasons if the program crashes EF migration builder won't notify you about it. So run the program on side to check if won't throw an exception right on the start.

Upvotes: 0

screamin

Reputation: 1241

If you are using the CLI,

When you have a solution with 2 projects API/WebApp and a DataAcess project you can pass in the options on the command line.

My_Solution
       |DataAccess_Project
       |-- DbContext.cs
       |WebApp_Project
       |-- Startup.cs

Change into the solution directory

CD My_Solution

dotnet ef migrations add InitialCreate --project DataAccess_Project --startup-project WebApp_Project

dotnet ef database update --project DataAccess_Project --startup-project WebApp_Project

Upvotes: 111

Mohsen Alizadeh

Reputation: 111

Just move your dbcontext config before builder.Build()

builder.Services.AddDbContext(options => options.UseSqlite(builder.Configuration.GetConnectionString("Default")));

var app = builder.Build();

Upvotes: 5

canariJaune

Reputation: 41

In Program.cs, I called builder.Build() before builder.Services.AddDbContext Just called builder.Build() at the end end it solved the problem

Upvotes: 1

Morteza Giti

Reputation: 19

I got the same error.

The Entity Framework tools version '6.0.1' is older than that of the runtime '6.0.6'. Update the tools for the latest features and bug fixes.

I updated the package and it worked.

Upvotes: -1

John

Reputation: 11

Just to add current info in case it helps someone on .Net 6.
In my case using .Net 6, and dotnet-ef version '6.0.4' the single key thing that made it work was ensuring the no-params constructor was present and public as in:

public TestContext()
{
}

My problem was that VS Code had created a protected constructor for me.
Some things that I tried that made NO difference:-

if your console app uses top-level statements or not,
NO need to have a TestContext(options) constructor.

Upvotes: 1

Ahmet Firat Keler

Reputation: 3996

Improving screamin's answer

I have a project structure like below

Solution

X.Api
...
...
X.Repository

My migrations are under X.Repository and my startup project is X.Api. After setting everything decently, without any code errors, I could not run my migrations using the command below

dotnet ef migrations add CreateABCTable

Applying the solution screamin suggested, I could run my migrations. I have used the command below

dotnet ef migrations add CreateABCTable --project X.Repository.csproj --startup-project ../X.Api/X.Api.csproj

Upvotes: 6

Nikolai Guryanov

Reputation: 83

in my case the reason of issue was the incorrect path to the dbsettings.json file. This path is should be written in the Startup.cs file.

 public Startup(Microsoft.AspNetCore.Hosting.IHostingEnvironment hostEnv)
    {
        _confString = new ConfigurationBuilder().SetBasePath(hostEnv.ContentRootPath).AddJsonFile("dbsettings.json").Build();
    
    }

Upvotes: 2

niek tuytel

Reputation: 1179

In your classes using DbContext set the constructor like:

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

Resource:
https://learn.microsoft.com/en-us/ef/core/dbcontext-configuration/

Upvotes: 1

mtdev

Reputation: 33

it's probably giving to you this problem, because you are using layered architecture. so you must factory desing pattern .for examlpe your context class must be like this below ;

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

       public class DesignTimeDbContextFactory : IDesignTimeDbContextFactory<ModelContext>
    {

                DbContextOptionsBuilder<ModelContext> builder = new DbContextOptionsBuilder<ModelContext>();               
                IConfiguration config = new ConfigurationBuilder()
                .SetBasePath(Path.Combine(Directory.GetCurrentDirectory(),"C:/Users/mücteba/source/repos/market/Market.API")) 
                       
                .AddJsonFile("appsettings.json")
                .Build();
           builder.UseSqlServer(config.GetConnectionString("SQLProvider"));
            return new ModelContext(builder.Options);
     }
  }
      DbSet<Personel> personels { get; set; }

this class is required if you use layered architecture!!!!

Upvotes: 3

James H

Reputation: 2401

Adding this variant of a solution in case it helps someone. I needed to create a migration in a simple console app and had to add an empty default .ctor to the DbContext class.

public TestContext()
{
}

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

Upvotes: 3

Julio Pereira

Reputation: 90

In my case, the problem was that Startup was not being detected in the way it was set in program:

public static IWebHostBuilder CreateWebHostBuilder(string[] args, Type startup)
{
   return WebHost.CreateDefaultBuilder(args).UseStartup(startup);
}

passing the type directly solved the problem:

.UseStartup<Startup>()

Upvotes: 0

Ivan Yurchenko

Reputation: 3871

EF needs to be able to get an instance of DbContext.

From an answer here:

Make sure you set the default startup project to the WebApplication.
Then in the Package Manager Console set the Default Project to the Data project. This will use the WebApplication configuration and add migrations to the Data project.

If you're running update-database command then you'll need to set the default project to your WebAPI project where the Startup.cs file is located.

Upvotes: 1

Volodymyr Neborachko

Reputation: 471

Make sure you have default constructor of IdentityContext without parameters. It should work.

Upvotes: 36

Salih Kavaf

Reputation: 1145

If you're using the new .NET 5 top-level code feature, then it is definitely why the migration is breaking. Using top-level statements in the Program class makes it impossible for the EF Tools to access it as it includes neither a namespace nor a class name.

Top-level statements:

Console.WriteLine("Hello, World!");

Classic Program class:

namespace MyApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("Hello, World!");
        }
    }
}

If this is the case, then just go back to the classic pattern.

Upvotes: 8

Fagun

Reputation: 79

Create a method in the Program class named CreateWebHostBuilder. Move your main method body to that class and call that class from the Main method. New implementation would be:

public static void Main(string[] args)
{
    CreateWebHostBuilder(args).Build().Run();
}

public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
    ServiceHost.Create<Startup>(args)
                .UseRabbitMq()
                .Build()
                .Run();

ef tool looks around CreateWebHostBuilder method and returns error when failed to find any.

Upvotes: 6

C. Gabriel

Reputation: 641

My problem was that I didn't set my api project from the solution as Startup Project so it wouldn't find any Startup.cs or sth like that.

Upvotes: 39

JcMey3r

Reputation: 181

Seems like you implemented IdentityContext but somewhere in your app its still trying to reference DbContext. Make sure Identitycontext is extending DbContext.

https://learn.microsoft.com/en-us/ef/core/miscellaneous/configuring-dbcontext

EDIT: Implemented IDesignTimeDbContextFactory as stated in https://learn.microsoft.com/en-gb/ef/core/miscellaneous/cli/dbcontext-creation

Upvotes: 8

Unable to create an object of type &#39;DbContext&#39;

Answers (25)

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Unable to create an object of type 'DbContext'