Cannot resolve symbol GetConnectionstring

Question

I have a .NET Core 3.0 class library. It is my first time working with .NET Core

I want to connect to a database.

https://learn.microsoft.com/en-us/ef/core/miscellaneous/connection-strings shows exactly how to do it.

https://learn.microsoft.com/en-us/dotnet/api/microsoft.extensions.configuration.configurationextensions.getconnectionstring?view=dotnet-plat-ext-3.1 shows the method which exists in the Microsoft.Extensions.Configuration namespace

I can't access it.

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;  //no underlines and imported via Nuget

namespace Core.Cms.DAL
{
    public class Entities : DbContext
    {
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {  optionsBuilder.UseSqlServer(Microsoft.Extensions.Configuration.GetConnectionString(ConnectionString.SqlServerExpress));

        }
    }
}

Screenshot

Why do I not have the Microsoft.Extensions.Configuration.GetConnectionString() method available?

edit

Restarted rider - same issue

Entities.cs(17, 45): [CS0234] The type or namespace name 'GetConnectionString' does not exist in the namespace 'Microsoft.Extensions.Configuration' (are you missing an assembly reference?)

Answer 1

In .NET 6 you now use builder.Configuration.GetConnectionString like this

builder.Services.AddDbContext<ApplicationDBContext>(options => 
options.UseSqlServer(
builder.Configuration.GetConnectionString("DefaultConnection")
));

Answer 2

You should use the IConfiguration interface. you can access to configuration form DI like this

private readonly IConfiguration _configuration;
public Entities(IConfiguration configuration)
{
    _configuration = configuration
}

then use the _configuration.GetConnectionString(ConnectionString.SqlServerExpress) instead of Microsoft.Extensions.Configuration.GetConnectionString()

optionsBuilder.UseSqlServer(_configuration.GetConnectionString(ConnectionString.SqlServerExpress));

if you are using the Asp.Net Core Web Application, This is a better way to config DbContext in startup class

public Startup(IConfiguration configuration)
{
    Configuration = configuration;
}
public IConfiguration Configuration { get; set; }

services.AddDbContext<Entities>(options =>
{
    options.UseSqlServer(Configuration.GetConnectionString(ConnectionString.SqlServerExpress));
});

Update

if you don't use the DI you can access to IConfiguration manually.

first you must install this packages

• Microsoft.Extensions.Configuration.Json

• Microsoft.Extensions.Configuration.FileExtensions

then build the IConfiguration

IConfiguration configuration = new ConfigurationBuilder()
   .AddJsonFile("appsettings.json", true,true)
   .Build();
optionsBuilder.UseSqlServer(configuration.GetConnectionString(ConnectionString.SqlServerExpress));