AddDbContext not available in IServiceCollection in .NET Core

Question

I have .NET Core 2 project in Visual Studio 2017. I am trying to add (Postgresql) database connection. Here is a code:

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext(options =>
        options.UseNpgsql(Configuration.GetConnectionString("DefaultConnection")));

    // Add framework services.
    services.AddMvc();
}

But compiler complains with this message:

IServiceCollection does not contain a definition for 'AddDbContext' and no extension method 'AddDbContext' accepting a first argument of type 'IServiceCollection' could be found (are you missing a using directive or an assembly reference?)

I installed NuGet package Npgsql. I also tried to install NuGet package EntityFramework, but I'm receiving error:

Package restore failed. Rolling back package changes for 'MyProject'.

Is this the root of my problem? Should I install some other library?

On this question procedures AddEntityFramework() and AddEntityFrameworkNpgsql() are used, but those two are also not recognized by compiler in my project.

Answer 1

Make sure you installed related NuGet packages with the right version for example

Microsoft.EntityFrameworkCore v3

and are using the right namespace such as

using Microsoft.EntityFrameworkCore;

using Microsoft.Extensions.DependencyInjection;

Answer 2

I installed Npgsql.EntityFrameworkCore.PostgreSQL and that resolved my issue. I also used Danijel's suggestion:

services.AddDbContext<ClassDbContextName>(options =>
            options.UseNpgsql(Configuration.GetConnectionString("DefaultConnection")));

Answer 3

Adding using Microsoft.Extensions.DependencyInjection fixed this issue for me.