How to get all columns in SQL Server

How to check if a column exists in a SQL Server database using VB.NET. This code uses ADO.NET to execute a query that checks for the existence of a column in a specified table.

To return the list of column names that exist in a SQL table, you can use the following SQL query along with a VB.NET implementation. Here’s a complete example to achieve that.

SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'YourTableName';

 

Example in VB.NET

Here’s how to implement this in VB.NET, retrieving the column names for a specific table:

 

Imports System.Data.SqlClient  Module Module1     Sub Main()         Dim connectionString As String = "YourConnectionStringHere"         Dim tableName As String = "YourTableName" ' Replace with your actual table name          Using connection As New SqlConnection(connectionString)             connection.Open()             Dim query As String = "SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS " & _                                   "WHERE TABLE_NAME = @TableName"              Using command As New SqlCommand(query, connection)                 command.Parameters.AddWithValue("@TableName", tableName)                  Using reader As SqlDataReader = command.ExecuteReader()                     If reader.HasRows Then                         Console.WriteLine("Columns in table '" & tableName & "':")                         While reader.Read()                             Console.WriteLine(reader("COLUMN_NAME").ToString())                         End While                     Else                         Console.WriteLine("No columns found in the specified table.")                     End If                 End Using             End Using         End Using     End Sub End Module

 

Explanation

1. Connection String: Replace "YourConnectionStringHere" with your actual connection string.
2. Table Name: Set tableName to the name of the table you want to check (replace YourTableName).
3. SQL Query: The query retrieves the column names from the INFORMATION_SCHEMA.COLUMNS view.
4. Parameters: Uses a parameter to safely pass the table name.
5. Data Reader: Executes the query and reads the results. If columns are found, it prints each column name.

This code will output the list of column names for the specified table.

Role of Kestrel server in .Net Core

Kestrel is a cross-platform web server built into ASP.NET Core and is used to handle HTTP requests. It is the default web server that comes with .NET Core applications. Here’s a breakdown of Kestrel's role and importance in .NET Core applications:

1. Default Web Server for ASP.NET Core:

• When you create and run an ASP.NET Core application, Kestrel is the underlying server that processes HTTP requests.

• It is designed to be lightweight and fast, suitable for high-performance scenarios.

2. Cross-Platform Compatibility:

• Kestrel is cross-platform, meaning it runs on Windows, Linux, and macOS.

• This aligns with the overall .NET Core philosophy of being cross-platform.

3. High Performance:

• Kestrel is optimized for speed and can handle a large number of concurrent connections, making it a great option for microservices or APIs.

• It leverages asynchronous I/O and is built on top of libuv (originally), a high-performance library that provides event-driven asynchronous I/O. In newer versions, Kestrel uses managed sockets.

4. Designed for Both Internal and External Requests:

• Kestrel can be used as an internet-facing server (directly handling requests from clients over the web) or as a reverse proxy server behind other servers (like IIS or Nginx).

• In production, Kestrel is often used behind a reverse proxy (like IIS, Nginx, or Apache) for additional security features like request filtering, SSL termination, and load balancing.

5. Configurable:

• Kestrel allows you to configure various options like port binding, SSL, request size limits, and logging.

• For example, you can bind Kestrel to specific IP addresses and ports by configuring it in the Program.cs or appsettings.json file.

6. Security:

• While Kestrel is fast and lightweight, it lacks some of the advanced security features found in traditional web servers (such as IIS or Nginx). Therefore, it’s often recommended to use it in conjunction with a reverse proxy in production environments.

Summary of Use Cases:

• Development and Testing: Kestrel can be used standalone during development for fast iteration.

• Production: In production environments, Kestrel is often paired with a reverse proxy for handling external traffic.

Example of Kestrel in ASP.NET Core:

In the Program.cs file of an ASP.NET Core application, Kestrel is typically configured like this:

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.UseKestrel();  // This configures Kestrel as the web server              webBuilder.UseStartup<Startup>();          }); }

In summary, Kestrel is an integral part of .NET Core applications, offering high performance, flexibility, and cross-platform support as a web server. It is suitable for both development and production environments (especially when used with a reverse proxy for the latter).

(image taken from wiki)

How does dependency injection work in .NET Core?

 Dependency Injection (DI) is a design pattern in which an object receives its dependencies from external sources rather than creating them itself. This pattern promotes loose coupling between components and increases testability.

In .NET Core, DI is built-in, making it easy to implement. It allows you to register services (interfaces and their implementations) with a built-in IoC (Inversion of Control) container, and the container automatically injects the services where needed.

How Dependency Injection Works in .NET Core

1. Service Registration: You register the services (interfaces and their implementations) in the Startup.cs file in the ConfigureServices method.

2. Service Resolution: The framework resolves dependencies and injects them into constructors, methods, or properties where needed.

3. Service Lifetime: .NET Core provides three main lifetimes for services:

• Transient: A new instance is created every time the service is requested.

• Scoped: A new instance is created per request (or per scope).

• Singleton: A single instance is created and shared throughout the application lifetime.

Example of Setting Up Dependency Injection in a .NET Core Application

Here’s a simple example demonstrating how to set up DI in a .NET Core application.

1. Define a Service Interface and Its Implementation

// Services/IMyService.cs public interface IMyService { string GetMessage(); } // Services/MyService.cs public class MyService : IMyService { public string GetMessage() {      return "Hello from MyService!"; } }

2. Register the Service in Startup.cs

In .NET Core, you register services in the ConfigureServices method inside Startup.cs

// Startup.cs public class Startup { public void ConfigureServices(IServiceCollection services) {      // Register the service with a transient lifetime      services.AddTransient<IMyService, MyService>();            // Other services like MVC can be added here as well      services.AddControllersWithViews(); } public void Configure(IApplicationBuilder app, IWebHostEnvironment env) {      // Usual configuration for middleware      if (env.IsDevelopment())      {          app.UseDeveloperExceptionPage();      }      else      {          app.UseExceptionHandler("/Home/Error");          app.UseHsts();      }      app.UseHttpsRedirection();      app.UseStaticFiles();      app.UseRouting();      app.UseAuthorization();      app.UseEndpoints(endpoints =>      {          endpoints.MapControllerRoute(              name: "default",              pattern: "{controller=Home}/{action=Index}/{id?}");      }); } }

3. Inject the Service in a Controller

Once the service is registered, you can inject it into a controller or any other class by simply adding it to the constructor.

// Controllers/HomeController.cs public class HomeController : Controller { private readonly IMyService _myService; // Constructor injection public HomeController(IMyService myService) {      _myService = myService; } public IActionResult Index() {      // Use the service      var message = _myService.GetMessage();      ViewBag.Message = message;      return View(); } }

4. Use the Service in the View

<!-- Views/Home/Index.cshtml --> @{ ViewBag.Title = "Home Page"; } <h2>@ViewBag.Message</h2>

Service Lifetimes in DI

• Transient (AddTransient<TService, TImplementation>()): A new instance of the service is created each time it is requested.

• Scoped (AddScoped<TService, TImplementation>()): A new instance is created once per request.

• Singleton (AddSingleton<TService, TImplementation>()): A single instance is shared across the entire application.

Benefits of Using DI

• Loose Coupling: Classes are decoupled from the concrete implementations of their dependencies.

• Testability: Dependencies can be mocked or replaced for testing.

• Maintainability: Centralized service configuration makes it easier to manage dependencies.

(image taken from wiki)