What is wrong with this code. Why can't I use SqlConnection?

I am 100% newbie to SQl and wanted to make a ConsoleApp with the use of database. I read some about it and tried. When I needed to make SqlConnection, my VS 2019 Preview showed me this

Severity Code Description Project File Line Suppression State Error CS1069 The type name 'SqlConnection' could not be found in the namespace 'System.Data.SqlClient'. This type has been forwarded to assembly 'System.Data.SqlClient, Version=0.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' Consider adding a reference to that assembly. ConsoleApp1 C:\Users\User\Desktop\Bald Code\ConsoleApp1\ConsoleApp1\Program.cs 12 Active

i don't get why it doesn't work

Here's my code

using System;

using System.Data;

using System.Data.SqlClient;

namespace ConsoleApp1

{

    class Program
    {
        static void Main(string[] args)
        {
            string connectionString;
            SqlConnection cnn;
        }
    }
}

If you just updated EntityFrameworkCore from version 2.x to 3.x and you're running into this, change your using statement to Microsoft.Data.SqlClient instead of System.Data.SqlClient.

If you're using EntityFrameworkCore.SqlServer it already has that as a dependency, so you shouldn't need to install it explicitly.

This Microsoft blog explains the change.

Assuming that you're using .NET Core - just add NuGet package: System.Data.SqlClient

Your .csproj might look similar to:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp2.1</TargetFramework>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="System.Data.SqlClient" Version="4.5.1" />
  </ItemGroup>
</Project>

Most likely the System.Data.SqlClient.DLL in not in the Bin folder, and you have not set reference to the DLL in the project. You have missed the database choice when You install visual studio. And now You just manually add references named "System.Data.SqlClient".

1.right click you project name and choose nuget package options.

2.search "System.Data.SqlClient" and install it.

Hope this is fix Your Error

The specific way to fix this from within VS Code is to

1. Open a terminal by going to Terminal -> New Terminal

2. Run dotnet add package System.Data.SqlClient

3. Run dotnet restore

That last command might not be necessary, but doing this made it work for me. It seems that console app templates don't come prepared for a reference to SqlClient.

Update

I think moving forward projects should use Microsoft.Data.SqlClient and not System.Data.SqlClient: https://devblogs.microsoft.com/dotnet/introducing-the-new-microsoftdatasqlclient/.

As @Mmm mentioned in the comments if you are using .NET Core and have already installed the System.Data.SqlClient package, closing and reopening the project resolved the issue for me too.