How to use program.cs from startup.cs in .NET 6/7?

I try to follow a tutorial online how to integrate Flutter with an ASP.NET Core Web API, the problem is the tutorial is outdated and requires me to create an ASP.NET Core 6 instead of 5.

This is code from startup.cs that been deprecated in .NET 6:

using System;
using AutoMapper;
using fixit.Data;
using fixit.Models;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

using System.Text;

// using Pomelo.EntityFrameworkCore.MySql;
// using fixit.Service;

namespace fixit
{   
    public class Startup
    {   
        readonly string AllowedOrigin = "allowedOrigin";

        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<DataContext>(opt => opt.UseSqlServer(Configuration.GetConnectionString("fixItConnection")));
            services.AddAutoMapper(AppDomain.CurrentDomain.GetAssemblies());

           services.AddCors(option =>
            {
                option.AddPolicy("allowedOrigin",
                    builder => builder.AllowAnyOrigin().AllowAnyMethod().AllowAnyHeader()
                    );
            });

            services.AddControllers();

            services.AddScoped<IRepository<Service>, ServiceRepository>();
        }

        // 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.UseCors(AllowedOrigin);
            app.UseHttpsRedirection();

            app.UseRouting();

            app.UseAuthentication();
            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }
    }
}

And this is program.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace fixit
{
    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>();
                });
    }
}

I tried to write program.cs in .NET 6, but the app can't be built.

This is my program.cs:

using fixit.Data;
using fixit.Models;
using Microsoft.Data.SqlClient;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddControllers();
builder.Services.AddScoped<IRepository<Service>, ServiceRepository>();

builder.Services.AddCors(option =>
  {
      option.AddPolicy("allowedOrigin",
          builder => builder.AllowAnyOrigin().AllowAnyMethod().AllowAnyHeader()
          );
  });

var app = builder.Build();

// For production scenarios, consider keeping Swagger configurations behind the environment check
// if (app.Environment.IsDevelopment())
// {
    app.UseSwagger();
    app.UseSwaggerUI();
// }

app.UseHttpsRedirection();

string connectionString = app.Configuration.GetConnectionString("AZURE_SQL_CONNECTIONSTRING")!;

try
{
    // Table would be created ahead of time in production
    using var conn = new SqlConnection(connectionString);
    conn.Open();

    var command = new SqlCommand(
        "CREATE TABLE Service (ID int NOT NULL PRIMARY KEY IDENTITY, servicename varchar(255), description varchar(255), category varchar(255), initialprice );",
        conn);
    using SqlDataReader reader = command.ExecuteReader();
}
catch (Exception e)
{
    // Table may already exist
    Console.WriteLine(e.Message);
}

app.MapGet("/Service", () => {
    var rows = new List<string>();

    using var conn = new SqlConnection(connectionString);
    conn.Open();

    var command = new SqlCommand("SELECT * FROM Service", conn);
    using SqlDataReader reader = command.ExecuteReader();

    if (reader.HasRows)
    {
        while (reader.Read())
        {
            rows.Add($"{reader.GetInt32(0)}, {reader.GetString(1)}, {reader.GetString(2)}");
        }
    }

    return rows;
})
.WithName("GetPersons")
.WithOpenApi();

app.MapPost("/Service", (Service person) => {
    using var conn = new SqlConnection(connectionString);
    conn.Open();

    var command = new SqlCommand(
        $"INSERT INTO Service (serviceid, servicename, description, category,initialprice,intermediateprice,advanceprice) VALUES ('{person.ServiceId}', '{person.ServiceName}','{person.Description}','{person.Category}','{person.InitialPrice}','{person.IntermediatePrice}','{person.AdvancedPrice}')",
        conn);

    using SqlDataReader reader = command.ExecuteReader();
})
.WithName("CreatePerson")
.WithOpenApi();

app.Run();

How to solve this?

Refer to this Docs, If you wanna use .WithOpenApi() in minimal API, You need to use .Net 7 instead of .Net6.

From your code, You seem to wanna use Minimal api instead of controller Api, So when you create Web Api project with template, You can uncheck this option to create a minimal api:

Here I modified some of your code to make it executable demo, Hope it can give you some help.

Model

public class Service
{
public string ServiceName { get; set; }
public string Description { get; set; }
public string Category { get; set; }
public int InitialPrice { get; set; }
public int IntermediatePrice { get; set; }
public int AdvancedPrice { get; set; }
}

Program.cs

using Microsoft.Data.SqlClient;
namespace MinmalApi
{
public class Program
{
public static void Main(string[] args)
{
var MyAllowSpecificOrigins = "_myAllowSpecificOrigins";
var builder = WebApplication.CreateBuilder(args);
// Add services to the container.
builder.Services.AddAuthorization();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddCors(option =>
{
option.AddPolicy("MyAllowSpecificOrigins",
builder => builder.AllowAnyOrigin().AllowAnyMethod().AllowAnyHeader()
);
});
//register other service.
var app = builder.Build();
// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
app.UseSwagger();
app.UseSwaggerUI();
}
app.UseHttpsRedirection();
app.UseCors(MyAllowSpecificOrigins);
string connectionString = app.Configuration.GetConnectionString("default")!;
try
{
// Table would be created ahead of time in production
using var conn = new SqlConnection(connectionString);
conn.Open();
var command = new SqlCommand(
"CREATE TABLE Service (ID int NOT NULL PRIMARY KEY IDENTITY, servicename varchar(255), description varchar(255), category varchar(255), initialprice int,IntermediatePrice int,AdvancedPrice int);",
conn);
using SqlDataReader reader = command.ExecuteReader();
}
catch (Exception e)
{
// Table may already exist
Console.WriteLine(e.Message);
}
app.MapGet("/Service", () =>
{
var rows = new List<string>();
using var conn = new SqlConnection(connectionString);
conn.Open();
var command = new SqlCommand("SELECT * FROM Service", conn);
using SqlDataReader reader = command.ExecuteReader();
if (reader.HasRows)
{
while (reader.Read())
{
rows.Add($"{reader.GetInt32(0)}, {reader.GetString(1)}, {reader.GetString(2)}");
}
}
return rows;
})
.WithName("GetPersons");
app.MapPost("/Service", (Service person) =>
{
using var conn = new SqlConnection(connectionString);
conn.Open();
var command = new SqlCommand(
$"INSERT INTO Service ( servicename, description, category,initialprice,IntermediatePrice,AdvancedPrice) VALUES ('{person.ServiceName}','{person.Description}','{person.Category}','{person.InitialPrice}','{person.IntermediatePrice}','{person.AdvancedPrice}')",
conn);
using SqlDataReader reader = command.ExecuteReader();
})
.WithName("CreatePerson");
app.Run();
}
}
}

Gif Demo

From the gif demo you can see that all endpoints are working fine.