Get ConnectionString from appsettings.json instead of being hardcoded in .NET Core 2.0 App

STEP 1: Include the following in OnConfiguring()

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        IConfigurationRoot configuration = new ConfigurationBuilder()
            .SetBasePath(AppDomain.CurrentDomain.BaseDirectory)
            .AddJsonFile("appsettings.json")
            .Build();
        optionsBuilder.UseSqlServer(configuration.GetConnectionString("DefaultConnection"));
    }

STEP 2: Create appsettings.json:

  {
    "ConnectionStrings": {       
      "DefaultConnection": "Server=YOURSERVERNAME; Database=YOURDATABASENAME; Trusted_Connection=True; MultipleActiveResultSets=true"        
    } 
  }

STEP 3: Hard copy appsettings.json to the correct directory

  Hard copy appsettings.json.config to the directory specified in the AppDomain.CurrentDomain.BaseDirectory directory. 
  Use your debugger to find out which directory that is.        

Assumption: you have already included package Microsoft.Extensions.Configuration.Json (get it from Nuget) in your project.

In ASPNET Core you do it in Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<BloggingContext>(options =>
        options.UseSqlServer(Configuration.GetConnectionString("BloggingDatabase")));
}

where your connection is defined in appsettings.json

{
  "ConnectionStrings": {
    "BloggingDatabase": "..."
  },
}

Example from MS docs

I understand this has been marked as answered but I ran into a bit of a problem when I was working on a project where I have my EF Core Data Access Layer in a .DLL Project separated from the rest of my project, API, Auth and Web and mostly will like my other projects to reference this Data project. And I don't want to want to come into the Data project to change connection strings everytime.

STEP 1: Include this in the OnConfiguring Method

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
      {
           var envName = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");
           IConfigurationRoot configuration = new ConfigurationBuilder()
                **.SetBasePath(Path.Combine(Directory.GetCurrentDirectory()))**
                .AddJsonFile("appsettings.json", optional: false)
                .AddJsonFile($"appsettings.{envName}.json", optional: false)
                .Build();
           optionsBuilder.UseSqlServer(configuration.GetConnectionString("DefaultConnection"));
      }

NOTE: .SetBasePath(Path.Combine(Directory.GetCurrentDirectory())) This will negate or invalidate the need to copy the file to a directory as ASP.NET CORE is smart enough to pick the the right file. Also the environment specified will pick right file when the building for Release or Production, assuming the Prod environment file is selected.

STEP 2: Create appsettings.json

{
"ConnectionStrings": {       
  "DefaultConnection": "Server=YOURSERVERNAME; Database=YOURDATABASENAME; Trusted_Connection=True; MultipleActiveResultSets=true"        
} 

}

PLEASE: Referece: Microsoft.Extensions.Configuration