To give you some context I have been trying to learn more about .NET and the EF Core ORM. But it seems like the more I try the less I understand.

As of right now I still can't reliable create a boilerplate for a simple application. Sometimes It breaks sometimes It works sometimes I just don't know what to do.

The problem I most encounter most frequently is this one:

Unable to create a 'DbContext' of type 'RuntimeType'. The exception 'Unable to resolve service for type 'Microsoft.EntityFrameworkCore.DbContextOptions`1[MVC___FreeCodeCamp.Data.MyAppContext]' while attempting to activate 'MVC___FreeCodeCamp.Data.MyAppContext'.' was thrown while attempting to create an instance. For the different patterns supported at design time, see /?linkid=851728

Now the first few times I get it. Hell I even "fixed" it. But thing is.. I don't understand it. Why does it come out? What does it even mean when it tells me I am using a different design pattern.

It probably means I am doing it wrong. And I get that. But I am currently copying a tutorial I saw.

I am not sure if the design pattern is really the problem here.

These are the relevant parts of my code:

The DbContext:

using Microsoft.EntityFrameworkCore;
using MVC___FreeCodeCamp.Models;

namespace MVC___FreeCodeCamp.Data;
    
public class MyAppContext : DbContext
{
    public MyAppContext(DbContextOptions<MyAppContext> options) :base(options) { }
    
    public DbSet<Item> Items { get; set; }
}

The program.cs relevant code:

builder.Services.AddDbContext<MyAppContext>(options => options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultString")));

The connection string:

"ConnectionStrings": {
    "DefaultString": "Server=localhost,1433;Database=FreeCodeCampMvc;User ID=sa;Password=<YourPassword>;Trusted_Connection=False;Encrypt=False;"  
}

Also the simple model in case it's necessary:

namespace MVC___FreeCodeCamp.Models;

public class Item
{
    public int Id { get; set; }
    public string Name { get; set; }
}

As you can see is as bare bone as it gets. Yet it doesn't work. Now to be fair I am currently running this app in .NET 9, Ubuntu 24.04 on JetBrains and I have the SQL Server running locally on a docker container. Hence the port in the connection string.

But it has worked in the past! I have all EF Core relevant nugets installed. I just don't understand. Why?

To give you some context I have been trying to learn more about .NET and the EF Core ORM. But it seems like the more I try the less I understand.

As of right now I still can't reliable create a boilerplate for a simple application. Sometimes It breaks sometimes It works sometimes I just don't know what to do.

The problem I most encounter most frequently is this one:

Unable to create a 'DbContext' of type 'RuntimeType'. The exception 'Unable to resolve service for type 'Microsoft.EntityFrameworkCore.DbContextOptions`1[MVC___FreeCodeCamp.Data.MyAppContext]' while attempting to activate 'MVC___FreeCodeCamp.Data.MyAppContext'.' was thrown while attempting to create an instance. For the different patterns supported at design time, see https://go.microsoft/fwlink/?linkid=851728

Now the first few times I get it. Hell I even "fixed" it. But thing is.. I don't understand it. Why does it come out? What does it even mean when it tells me I am using a different design pattern.

It probably means I am doing it wrong. And I get that. But I am currently copying a tutorial I saw.

I am not sure if the design pattern is really the problem here.

These are the relevant parts of my code:

The DbContext:

using Microsoft.EntityFrameworkCore;
using MVC___FreeCodeCamp.Models;

namespace MVC___FreeCodeCamp.Data;
    
public class MyAppContext : DbContext
{
    public MyAppContext(DbContextOptions<MyAppContext> options) :base(options) { }
    
    public DbSet<Item> Items { get; set; }
}

The program.cs relevant code:

builder.Services.AddDbContext<MyAppContext>(options => options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultString")));

The connection string:

"ConnectionStrings": {
    "DefaultString": "Server=localhost,1433;Database=FreeCodeCampMvc;User ID=sa;Password=<YourPassword>;Trusted_Connection=False;Encrypt=False;"  
}

Also the simple model in case it's necessary:

namespace MVC___FreeCodeCamp.Models;

public class Item
{
    public int Id { get; set; }
    public string Name { get; set; }
}

As you can see is as bare bone as it gets. Yet it doesn't work. Now to be fair I am currently running this app in .NET 9, Ubuntu 24.04 on JetBrains and I have the SQL Server running locally on a docker container. Hence the port in the connection string.

But it has worked in the past! I have all EF Core relevant nugets installed. I just don't understand. Why?

• c#
• asp-core
• -core
• entity-framework-core
• asp-core-mvc

1 Answer 1

The error indicates when the Dependency injection system try to create an instance of MyAppContext it requires DbContextOptions<MyAppContext> options for you defined the constructor of the DbContext as :

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

However,it cound't find DbContextOptions<MyAppContext> in DI container.

For you've injected the options with the codes:

builder.Services.AddDbContext<MyAppContext>(options => options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultString")));

You could check if you configured the wrong project(which project contains the DbContext class) &startup project (the project you injected dbcontext with builder.Services.AddDbContext) which caused the DI system failed to find required options when you add migration.

You may check this issue related