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 lt AppContext gt        public AppContext CreateDbContext string   args                var builder   new DbContextOptionsBuilder lt AppContext gt             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 lt AppContext gt  options   gt  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 lt AppContext gt         builder UseSqlServer connectionString        return new AppContext builder Options

User · Answer

There is actually a default pattern that you can employ to achieve this result without having to implement IDesignTimeDbContextFactory and do any config file copying.

It is detailed in this doc, which also discusses the other ways in which the framework will attempt to instantiate your DbContext at design time.

Specifically, you leverage a new hook, in this case a static method of the form public static IWebHost BuildWebHost(string[] args). The documentation implies otherwise, but this method can live in whichever class houses your entry point (see src). Implementing this is part of the guidance in the 1.x to 2.x migration document and what's not completely obvious looking at the code is that the call to WebHost.CreateDefaultBuilder(args) is, among other things, connecting your configuration in the default pattern that new projects start with. That's all you need to get the configuration to be used by the design time services like migrations.

Here's more detail on what's going on deep down in there:

While adding a migration, when the framework attempts to create your DbContext, it first adds any IDesignTimeDbContextFactory implementations it finds to a collection of factory methods that can be used to create your context, then it gets your configured services via the static hook discussed earlier and looks for any context types registered with a DbContextOptions (which happens in your Startup.ConfigureServices when you use AddDbContext or AddDbContextPool) and adds those factories. Finally, it looks through the assembly for any DbContext derived classes and creates a factory method that just calls Activator.CreateInstance as a final hail mary.

The order of precedence that the framework uses is the same as above. Thus, if you have IDesignTimeDbContextFactory implemented, it will override the hook mentioned above. For most common scenarios though, you won't need IDesignTimeDbContextFactory.

User · Answer

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

User · Answer

In ASPNET Core you do it in Startup cs  public void ConfigureServices IServiceCollection services        services AddDbContext lt BloggingContext gt  options   gt          options UseSqlServer Configuration GetConnectionString  BloggingDatabase          where your connection is defined in appsettings json       ConnectionStrings          BloggingDatabase                  Example from MS docs

User · Answer

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

User · Answer

You can also do this in ASP NET Core 2 by defining the connection string in your appSettings json file  Then in your Startup cs you specify which connection string to use     appSettings json         connectionStrings              YourDBConnectionString    Server  localdb   mssqllocaldb Database YourDB Trusted Connection True            Startup cs  public static IConfiguration Configuration   get  private set    public Startup IConfiguration configuration        Configuration   configuration    var connectionString   Configuration  connectionStrings YourDBConnectionString    services AddDbContext lt YourDbContext gt  x   gt  x UseSqlServer connectionString

User · Answer

How about passing it as dp injection into that class  in ConfigureServices   services Configure lt MyOptions gt  Configuration     create class to hold json strings   public class MyOptions       public MyOptions                    public string Option1   get  set        public string Option2   get  set            Add strings to json file    option1    somestring    option2    someothersecretstring    In classes that need these strings  pass in as constructor   public class SomeClass    private readonly MyOptions  options       public SomeClass IOptions lt MyOptions gt  options                 options   options Value                         public void UseStrings         var option1    options Option1      var option2    options Option2     code

User · Answer

If you need in different Layer    Create a Static Class and expose all config properties on that layer as below     x000D   x000D  using Microsoft Extensions Configuration  x000D  using System IO  x000D   x000D  namespace Core DAL x000D    x000D      public static class ConfigSettings x000D        x000D          public static string conStr1   get     x000D          static ConfigSettings   x000D            x000D              var configurationBuilder   new ConfigurationBuilder    x000D              string path   Path Combine Directory GetCurrentDirectory     appsettings json    x000D              configurationBuilder AddJsonFile path  false   x000D              conStr1   configurationBuilder Build   GetSection  ConnectionStrings ConStr1   Value  x000D            x000D        x000D    x000D   x000D   x000D

User · Answer

Add the following code into startup cs file   public void ConfigureServices IServiceCollection services        string con   Configuration GetConnectionString  DBConnection        services AddMvc        GlobalProperties DBConnection   con   DBConnection is a user defined static property of GlobalProperties class    Use GlobalProperties DBConnection property in Context class   protected override void OnConfiguring DbContextOptionsBuilder optionsBuilder        if   optionsBuilder IsConfigured                    optionsBuilder UseSqlServer GlobalProperties DBConnection

User · Answer

There are a couple things missing  both from the solutions above and also from the Microsoft documentation   If you follow the link to the GitHub repository linked from the documentation above  you ll find the real solution   I think the confusion lies with the fact that the default templates that many people are using do not contain the default constructor for Startup  so people don t necessarily know where the injected Configuration is coming from   So  in Startup cs  add    public IConfiguration Configuration   get     public Startup IConfiguration configuration           Configuration   configuration       and then in ConfigureServices method add what other people have said     services AddDbContext lt ChromeContext gt  options   gt                          options UseSqlServer Configuration GetConnectionString  DatabaseConnection        you also have to ensure that you ve got your appsettings json file created and have a connection strings section similar to this       ConnectionStrings          DatabaseConnection    Server MyServer Database MyDatabase Persist Security Info True User ID SA Password PASSWORD MultipleActiveResultSets True           Of course  you will have to edit that to reflect your configuration   Things to keep in mind   This was tested using Entity Framework Core 3 in a  Net Standard 2 1 project  I needed to add the nuget packages for  Microsoft EntityFrameworkCore 3 0 0 Microsoft EntityFrameworkCore SqlServer 3 0 0 because that s what I m using  and that s what is required to get access to the UseSqlServer

User · Answer

It s not fancy I known but you could use a callback class  create a hostbuilder and set the configuration to a static property   For asp core 2 2   using Microsoft AspNetCore  using Microsoft AspNetCore Builder  using Microsoft AspNetCore Hosting  using Microsoft Extensions Configuration  using System   namespace Project       sealed class Program                region Variables              lt summary gt              Last loaded configuration              lt  summary gt          private static IConfiguration  Configuration           endregion           region Properties              lt summary gt              Default application configuration              lt  summary gt          internal static IConfiguration Configuration                       get                                  None configuration yet                  if  Program  Configuration    null                                           Create the builder using a callback class                     IWebHostBuilder builder   WebHost CreateDefaultBuilder   UseStartup lt CallBackConfiguration gt                             Build everything but do not initialize it                     builder Build                                          Current configuration                 return Program  Configuration                                Update configuration             set   gt  Program  Configuration   value                     endregion           region Public              lt summary gt              Start the webapp              lt  summary gt          public static void Main string   args                           Create the builder using the default Startup class             IWebHostBuilder builder   WebHost CreateDefaultBuilder args  UseStartup lt Startup gt                     Build everything and run it             using  IWebHost host   builder Build                    host Run                       endregion            region CallBackConfiguration              lt summary gt              Aux class to callback configuration              lt  summary gt          private class CallBackConfiguration                            lt summary gt                  Callback with configuration                  lt  summary gt              public CallBackConfiguration IConfiguration configuration                                   Update the last configuration                 Program Configuration   configuration                                  lt summary gt                  Do nothing  just for compatibility                  lt  summary gt              public void Configure IApplicationBuilder app  IHostingEnvironment env                                                                    endregion           So now on you just use the static Program Configuration at any other class you need it

[c#] Get ConnectionString from appsettings.json instead of being hardcoded in .NET Core 2.0 App

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