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

Question

I have the following class in NET Core2.0 App.

// required when local database does not exist or was deleted public class ToDoContextFactory : IDesignTimeDbContextFactory<AppContext> {     public AppContext CreateDbContext(string[] args)     {         var builder = new DbContextOptionsBuilder<AppContext>();         builder.UseSqlServer("Server=localhost;Database=DbName;Trusted_Connection=True;MultipleActiveResultSets=true");         return new AppContext(builder.Options);     } } 

This is required in Core 2.0 with migration when Database does not exist and has to be created when you run update-database.
Unable to create migrations after upgrading to ASP.NET Core 2.0

I would like not having ConnectionString in 2 places(here and in appsettings.json) but only in .json so I have tried to replace

"Server=localhost;Database=DbName;Trusted_Connection=True;MultipleActiveResultSets=true" 

with

ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString 

but it's not working, I'm getting null value.

UPDATE 1:
Just to note that adding explicitly .json is not necessery in Core 2 so the problem is not with the file.
https://andrewlock.net/exploring-program-and-startup-in-asp-net-core-2-preview1-2/

UPDATE 2:
Also I am already using Configuration for sending ConnectionString from .json to Context:

public class Startup {     public Startup(IConfiguration configuration)     {         Configuration = configuration;     }      public IConfiguration Configuration { get; }      public void ConfigureServices(IServiceCollection services)     {         services.AddDbContext<AppContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));     } } 

But I can not use this for ToDoContextFactory because it does not have Configuration, and ToDoContextFactory is used by migrations so the App is not running at all.

SOLUTION: Based on answer from @JRB I made it work like this:

public AppContext CreateDbContext(string[] args) {     string projectPath = AppDomain.CurrentDomain.BaseDirectory.Split(new String[] { @"bin\" }, StringSplitOptions.None)[0];     IConfigurationRoot configuration = new ConfigurationBuilder()         .SetBasePath(projectPath)         .AddJsonFile("appsettings.json")         .Build();     string connectionString = configuration.GetConnectionString("DefaultConnection");      var builder = new DbContextOptionsBuilder<AppContext>();     builder.UseSqlServer(connectionString);      return new AppContext(builder.Options); } 

Answer 1

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.

Answer 2

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