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How to add Startup.cs in existing project .net5

I have an .net5 project and in .csproj file I have this:
<PropertyGroup>
<TargetFramework>net5.0</TargetFramework>
</PropertyGroup>
I added Microsoft.EntityFrameworkCore package to my prject.furturemore I created Dbcontext file like below:
using Domian;
using Microsoft.EntityFrameworkCore;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
namespace Mc2.CrudTest.Presentation.Front.Infrastructure
{
public class DataContext : DbContext
{
protected readonly IConfiguration Configuration;
public DataContext(IConfiguration configuration)
{
Configuration = configuration;
}
protected override void OnConfiguring(DbContextOptionsBuilder options)
{
// connect to sql server with connection string from app settings
options.UseSqlServer(Configuration.GetConnectionString("SqlServerConnection"));
}
public DbSet<Customer> Customers { get; set; }
}
}
since there wasn't any startup.cs file in my project ,I created one this way:
the namespaces of IApplicationBuilder and IWebHostEnvironment coudn't find.
I dont know whether I can use startup.cs file like.net core.3.1 or I shouldn't use startup.cs file in .net5 anymore.
And my program.cs file was formed this way:
using System;
using System.Net.Http;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Components.WebAssembly.Hosting;
using Microsoft.Extensions.DependencyInjection;
namespace Mc2.CrudTest.Presentation.Front
{
public class Program
{
public static async Task Main(string[] args)
{
WebAssemblyHostBuilder builder = WebAssemblyHostBuilder.CreateDefault(args);
builder.RootComponents.Add<App>("#app");
builder.Services.AddScoped(_ => new HttpClient { BaseAddress = new Uri(builder.HostEnvironment.BaseAddress) });
await builder.Build().RunAsync();
builder.Services.AddDbContext(options => options
}
}
}
In addtion my project is BlazorWebAssembly

First of all, don't use .NET 5. It reached End-of-Life on May 2022. That's almost a year ago. EOL means no support at all, for anything, from either Microsoft or NuGet authors. Not even security patches.
It was known from the start this would be a single-year or "Standard-Term" Support version (STS), supported only for 18 months. The Long-Term-Support version is .NET 6, supported until November 2024. LTS versions are supported for 3 years since release.
Second, you don't need Startup.cs in .NET 6 (or .NET 5). The methods found in Startup.cs were merged into Program.cs. You can write :
builder.Services.AddDbContext(options=>options
.UseSqlServer(builder.Configuration.GetConnectionString("SqlServerConnection")));
This is shown in all ASP.NET Core and EF Core tutorials, eg this Web API tutorial. In this tutorial, Program.cs contains :
using Microsoft.EntityFrameworkCore;
using TodoApi.Models;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllers();
builder.Services.AddDbContext<TodoContext>(opt =>
opt.UseInMemoryDatabase("TodoList"));
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
var app = builder.Build();
if (app.Environment.IsDevelopment())
{
app.UseSwagger();
app.UseSwaggerUI();
}
app.UseHttpsRedirection();
app.UseAuthorization();
app.MapControllers();
app.Run();
Notice that even Program.Main is missing. That's the entire file. This is possible through a few new C# features: top-level statements and implied usings.
If you don't like this style you can use --use-program-main to generate a Program.cs and Main method

First off, of course you should update to .NET6 or .NET7 if you can[1]. But if that's not practical for whatever reason, then of course you can use startup.cs. In fact I prefer to as well, out of habit (you can use it in .NET6 too; not sure about 7 but I assume so).
You can define startup.cs more or less the way you do, but you do need the right using's:
using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.Hosting;
Less obviously, in your program.cs you need
using Microsoft.AspNetCore;
...
public static async Task Main(string[] args)
{
...
WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>()
.Build();
...
}
Edit - After discussing with Amir in comments below it seems the scope of this problem is pretty different from what was originally asked. I suggest you spend some time in an example Blazor solution with a separate hosting project from the webassembly SPA project. Things will make a lot more sense after that.
[1] Microsoft IMO has done the world a disservice with its post-Framework policy of introducing breaking changes into each ASP.NET version so liberally. It's not always just a matter of retargeting. And that's especially true of Blazor which is still so immature. Certainly if security is a concern for this application you should be doing everything you can to upgrade, but in the real world isn't always that simple.

you should add blazerServerApp project which consist of program.cs and startup.cs which you looking for as shown below.

.NET 6 Single-File ASP.NET template with Entity Framework Core

I am using the Visual Studio 2022/.NET 6 Razor pages template. It uses a top-level C# 10 program file. Program.cs looks something like this:
using Microsoft.EntityFrameworkCore;
using Data;
using Services;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddMemoryCache();
builder.Services.AddRazorPages();
var settings = builder.Configuration.Get<AppSettings>();
builder.Services
.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));
var app = builder.Build();
app.UseHttpsRedirection();
app.UseRouting();
app.MapRazorPages();
app.Run();
My DBContext looks like this
public class ApplicationDbContext: DbContext
{
public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : base(options) { }
internal DbSet<MyModel> MyModels { get; set; }
protected override void OnModelCreating(ModelBuilder builder){ /* ... */ }
}
When I run dotnet ef migrations add InitialMigration -v, I get the following error:
Finding DbContext classes...
Finding IDesignTimeDbContextFactory implementations...
Finding application service provider in assembly 'Data'...
Finding Microsoft.Extensions.Hosting service provider...
No static method 'CreateHostBuilder(string[])' was found on class 'Program'.
No application service provider was found.
Finding DbContext classes in the project...
Found DbContext 'ApplicationDbContext'.
Microsoft.EntityFrameworkCore.Design.OperationException: Unable to create an object of type 'ApplicationDbContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728
---> System.InvalidOperationException: Unable to resolve service for type 'Microsoft.EntityFrameworkCore.DbContextOptions`1[Data.DatabaseContext.ApplicationDbContext]' while attempting to activate 'Data.DatabaseContext.ApplicationDbContext'.
Visual Studio Add-Migration also fails to build, but provides no stack trace.
The provided link indicated that I might be able to add an implementation of IDesignTimeDbContextFactory to contain some startup code that might work.
I created this class, but it also seems to do nothing.
public class ApplicationContext: IDesignTimeDbContextFactory<ApplicationDbContext>
{
ApplicationDbContext IDesignTimeDbContextFactory<SanDiegoContext>.CreateDbContext(string[] args)
{
IConfigurationRoot configuration = MyStaticConfigurationBuilder.GetConfig();
var optionsBuilder = new DbContextOptionsBuilder<ApplicationDbContext>();
optionsBuilder.UseSqlServer(connectionString: configuration.GetConnectionString("DefaultConnection"));
return new ApplicationDbContext(optionsBuilder.Options);
}
}
Is it possible to use EF Core in .NET 6 without building a GetHostBuilder(string[]) method and a Startup class? If so, what am I doing wrong?

I made it work with the following steps:
Rebuild the project.
Make sure I was using Visual Studio Command Line Tools with the right project
Install Microsoft.EntityFrameworkCore.Design to my Web project
Make sure my project builds on its own with a standard CTRL-B or dotnet build
Then my startup looks like this:
using Microsoft.EntityFrameworkCore;
using Data;
using Services;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddMemoryCache();
builder.Services.AddRazorPages();
var settings = builder.Configuration.Get<AppSettings>();
builder.Services
.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));
var app = builder.Build();
app.UseHttpsRedirection();
app.UseRouting();
app.MapRazorPages();
app.Run();
and the migration attempts to scaffold as usual

How to exclude a .NET 6 Minimal API from code coverage?

I maintain a class library which contains several reference implementations to demonstrate how the library should be used. I have reference implementations for .Net Framework, core, .NET 5 and now I have added a reference implementation for .NET 6 using minimal APIs.
For all of my other reference implementations I have added the ExcludeFromCodeCoverage attribute using System.Diagnostics.CodeAnalysis to all of their containing classes. How would I do something similar for a .NET 6 minimal API?
My program.cs looks like this:
using Microsoft.AspNetCore.Mvc;
using SharedDataLayer.Repositories;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddSingleton<PaymentRepository>();
var app = builder.Build();
app.MapGet("/Payments", ([FromServices] PaymentRepository repo) =>
{
return repo.GetPayments();
});
app.Run();

Your Program.cs shoud look like this:
using Microsoft.AspNetCore.Mvc;
using SharedDataLayer.Repositories;
using System.Diagnostics.CodeAnalysis;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddSingleton<PaymentRepository>();
var app = builder.Build();
app.MapGet("/Payments", ([FromServices] PaymentRepository repo) =>
{
return repo.GetPayments();
});
app.Run();`
[ExcludeFromCodeCoverage]
public partial class Program { }

I've tested out the suggestions from #PanagiotisKanavos and #Tolvic in the comments on the initial question and can confirm that adding the following to the top of your program.cs does work and the file is excluded from code coverage.
using System.Diagnostics.CodeAnalysis;
[assembly: ExcludeFromCodeCoverage]

using System.Diagnostics.CodeAnalysis;
[assembly: ExcludeFromCodeCoverage]
worked for me

Having trouble with UseInMemoryDatabase ASP.NET Core 3.1

I was using this tutorial: Create a web API with ASP.NET Core but I get an error in Startup.cs after installing Microsoft.EntityFrameworkCore.SqlServer from Nuget.
The error message is:
Error CS1061 'DbContextOptionsBuilder' does not contain a definition for 'UseInMemoryDatabase' and no accessible extension method 'UseInMemoryDatabase' accepting a first argument of type 'DbContextOptionsBuilder' could be found (are you missing a using directive or an assembly reference?)
This instruction refers to this point in the project "Register the database context".
Here is the code for startup.cs:
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;
using TodoApi.Models;
namespace TodoApi
{
public class Startup
{
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<TodoContext>(opt =>
opt.UseInMemoryDatabase("TodoList"));
services.AddControllers();
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
app.UseHttpsRedirection();
app.UseRouting();
app.UseAuthorization();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllers();
});
}
}
}
I looked online but couldn't find any fix for this problem, I have to say I installed Microsoft.EntityFrameworkCore.SqlServer version 5.0, and in the tutorial is version 3.0 but I don't think this is the issue.
The error I get occurs here:
services.AddDbContext<TodoContext>(opt =>
opt.UseInMemoryDatabase("TodoList"));

The article you used explains that you need to add the Microsoft.EntityFrameworkCore.InMemory package in the section Add a Database Context, in the Add NuGet packages box :
Use the preceding instructions to add the Microsoft.EntityFrameworkCore.InMemory NuGet package
This package adds the provider and the UseInMemoryDatabase extension method

Try adding the package: Microsoft.EntityFrameworkCore.InMemory

Asp.Net Core How to Configure Migrations type to assembly

Hello everyone my name is Taniguchi and i learning asp.net core and I managed to create a migration but when I used the Update-Database command show me the following error: "
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
No migrations configuration type was found in the assembly 'WebApplication1'. (In Visual Studio you can use the Enable-Migrations command from Package Manager Console to add a migrations configuration).
my database:
public class MimicContext : DbContext
{
public MimicContext(DbContextOptions<MimicContext> options) : base(options)
{
}
public DbSet<Palavra> Palavras { get; set; }
}
my startup:
public class Startup
{
// This method gets called by the runtime. Use this method to add services to the container.
// For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<MimicContext>(opt =>
{
opt.UseSqlite("Data Source=Database\\Mimic.db");
});
services.AddMvc(options => options.EnableEndpointRouting = false);
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
app.UseMvc();
}
}
How can i configure a migration to the assembly ?

Have you enabled migrations in your project? If you didn't than use Enable-Migrations. I think that it could be the problem.

Before running the update command in PMC first enable it. For more details view this link here

Small mistake, but good learning for me after spending more than one day painful effort. I hope this will be the good learning for others too.
I have added two NuGet packages of: EntityFramework, and Microsoft.EntityFrameworkCore which is my mistake.
Just adding NuGet package for Microsoft.EntityFrameworkCore will do all the required work.