Add identity into an ASP.NET Core 2.1 MVC project and maintain full control of the Identity UI

To maintain full control over the Identity UI in an ASP.NET Core 2.1 MVC project, scaffold the identity using the Windows version of Visual Studio 2017.

Scaffold the Identity

  1. Right click the web application project and select Add, New Scaffolded Item
  2. On the left side of the Add Scaffold dialog select Identity, and click the Add button
  3. Select your existing Layout page, so the scaffolding will not overwrite it
  4. Select the Identity functions (files) you want to override, and click the down arrow to select your existing data context class
  5. The MY_SOLUTION\MY_WEBAPP\ScaffoldingReadme.txt file contains tasks to do to set up the Identity UI. Based on that
    1. Add the following lines to the Configure method of the Startup.cs file in this order. If a line is already in the file, make sure the order is correct.
    2. Add to the ConfigureServices method of the Startup.cs file, if the line is not there.
  6. The Aeras, Identity, Pages, Account folder contains the .cshtml files you can modify.
  7. The code is in the .cshtml.cs file

Use your own SMTP server

To configure Identity to use you own SMTP server to send the Forgot my password and email verification emails, register a custom email sender.

  1. Add to the ConfigureServices method of the Startup.cs file
    // using Microsoft.AspNetCore.Identity.UI.Services;
    services.AddSingleton<IEmailSender, EmailSender>();
  2. Create the EmailSender class in the web application project
    // using Microsoft.AspNetCore.Identity.UI.Services;
    // using System.Threading.Tasks;
    public class EmailSender : IEmailSender
        public Task SendEmailAsync(string sTo, string sSubject, string sMessage)
            MyMessagingClass messaging = new MyMessagingClass();
            // Send an email message with SMTP
            messaging.MySendEmailMethod(sTo, sSubject, sMessage);
            return Task.CompletedTask;

For more information see



Add jQuery DataTables grid to an ASP.NET Core MVC web application

ASP.NET does not provide sortable, searchable tables. jQuery DataTables is a popular way to display user-friendly data in an ASP.NET Core MVC web application.

Set up the environment

  1. Add the System.Linq.Dynamic.Core NuGet package to the web application
  2. Add the JsonOptions to the Startup.cs file
     using Newtonsoft.Json.Serialization;
  3. Add the AddJsonOptions to the services.AddMvc() section in the ConfigureServices() method of the Startup.cs file
     .AddJsonOptions(options => options.SerializerSettings.ContractResolver = new DefaultContractResolver());

Add the jQuery DataTables grid to the view

  1. Add the script and css references to the bottom of the view
    @section Scripts {
    	<!-- For the DataTables grid -->
    	<link rel="stylesheet" type="text/css" href="">
    	<script type="text/javascript" src=""></script>
    	<!-- Page-specific script -->
    	<script src="~/js/MY-CONTROLLER_MY-PAGE.js" asp-append-version="true"></script>
  2. Add to the page-specific MY-CONTROLLER_MY-PAGE.js file to the wwwroot\js directory
    $(document).ready(function () {
      // Set up the DataTable grid
  3. Create a table with the same id referenced in the script
    @if (null != Model.ServerList) {
      <table id="serverTable" class="table table-striped table-bordered dt-responsive nowrap" width="100%">
          @foreach (ServerInstance instance in Model.ServerList) {
              <td><input type="checkbox" asp-for="@instance.Selected" /></td>


Error unprotecting the session cookie in an ASP.NET Core MVC application.

The new ASP.NET Core MVC framework automatically displays a message for the user to accept the application’s privacy policy. The default message is “Use this space to summarize your privacy and cookie use policy.” No cookies are saved in the user’s browser until they click the Accept button.

Even after accepting the terms, if the browser contains old, stale cookies the application may not be able to save cookies. The log contains

warn: Microsoft.AspNetCore.Session.SessionMiddleware[7]
Error unprotecting the session cookie.
System.Security.Cryptography.CryptographicException: The key … was not found in the key ring.

If the web application works in a new incognito window, clear the old cookies in your browser.

In Google Chrome

  1. In the Chrome menu select Clear Browsing Data
  2. On the Clear browsing data page select All time, and Cookies and other site data



Set the environment for an ASP.NET Core MVC web application

When the ASP.NET Core MVC web application starts, reads the name of the environment for an environment variable of the host computer. The compiled application contains the configuration for all supported environments, making possible to build and deploy the same artifact in every environment.

If the ASPNETCORE_ENVIRONMENT environment variable is not defined, the Production environment settings are loaded.

In Visual Studio the web application project sets the value on the Debug tab.

To set the environment on the server


To set the value globally that is preserved after restart

Command prompt

  1. Open the command prompt window and execute
    setx ASPNETCORE_ENVIRONMENT Development /M


  1. Open a PowerShell window and execute
    [Environment]::SetEnvironmentVariable("ASPNETCORE_ENVIRONMENT", "Development", "Machine")


  1. Add to the .bashrc or .bash_profile file
    export ASPNETCORE_ENVIRONMENT=Development


Configure the ASP.NET Core MVC web application

Create the environment-specific appsettings.json files

  1. In the web application project click the arrow next to the appsettings.json file to reveal the Development configuration file
  2. Right-click the appsettings.Development.json file and select Copy

  3. Right click the web application project and select Paste

  4. Rename the appsettings – Copy.Development.json file to appsettings.Production.json

  5. The file will automatically move under the appsettings.json file

Edit the configuration files

  1. Open the appsettings.Production.json file and add the connection string
        "ConnectionStrings": {
            "DefaultConnection": "Server=MY_DATABASE_URL;Database=MY_DATABASE_NAME;Username=MY_USERNAME;Password=MY_PASSWORD"


Return values to the controller in the model from the ASP.NET MVC view

When we create an ASP.NET MVC web application, the model (an object) is the easiest way to return values from the view to the controller.

For the view to be able to return the values in the model, make sure the model contains properties, not fields, for every value with { get; set; }

public class MyViewModel
    public string ID { get; set; }

Add the model to the view at the top of the .cshtml file

IMPORTANT!!! To return values for properties that do not have controls on the page, like IDs that are not displayed, add a hidden field to the view.

@model MyViewModel
<form  asp-action="Index" asp-controller="My">
    <input asp-for=@Model.ID type="hidden" >

Send the data in the model to the view from the get method in the controller

public class MyController : Controller
    public IActionResult Index()
         MyViewModel model = new MyViewModel();
         model.ID = "MY_ID";
         return View(model);

Read the value from the model in the post method of the controller and send the model back

public class MyController : Controller
    [HttpPost, ValidateAntiForgeryToken]
    public IActionResult Index(MyViewModel model)
        string ID = model.ID;
        return View(model);


Reverse engineer a database with AspNetCore in Visual Studio

For some reason the .NETCore designers did not think, that developers want to follow best practices by separating the data layer from the presentation layer.

The Entity framework out of the box only works if the database is accessed from the main application project.

When we try to reverse engineer a PostgreSQL database from a class library with the command:

dotnet ef dbcontext scaffold "Host=localhost;Database=MY_DATABASE_NAME;Username=MY_USERNAME;Password=MY_PASSWORD" Npgsql.EntityFrameworkCore.PostgreSQL

we get the error message:

The specified framework version ‘2.1’ could not be parsed
The specified framework ‘Microsoft.NETCore.App’, version ‘2.1’ was not found.
– Check application dependencies and target a framework version installed at:
– Installing .NET Core prerequisites might help resolve this problem:
– The .NET Core framework and SDK can be installed from:
– The following versions are installed:
2.0.0 at [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
2.1.2 at [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
2.1.3 at [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

The problem is, that the …runtimeconfig.json files are only automatically generated in the bin/netcoreapp2.1 directory of the main application project, those are missing from all class libraries.

To enable the automatic generation of the …runtimeconfig.json files, add a line to the <PropertyGroup> section of the data layer class library project (.csproj) file.



The given assembly name or codebase was invalid. (Exception from HRESULT: 0x80131047)

When I made changes to the web.config file of an ASP.Net C# application, I have accidentally deleted a comma, and I started to get the runtime error message:

The given assembly name or codebase was invalid. (Exception from HRESULT: 0x80131047)

Make sure all necessary commas are there in the config files, Visual Studio does not check the format of those lines. In my case, the error was in

<provider invariantName="MySql.Data.MySqlClient" type="MySql.Data.MySqlClient.MySqlProviderServices, MySql.Data.Entity.EF6, Version=, Culture=neutral, PublicKeyToken=c5687fc88969c44d" />

{“error”:”Entity type ‘AspNetUserRoles’ has composite primary key defined with data annotations. To set composite primary key, use fluent API.”}

When a database table has composite keys (multiple columns are in the key) you cannot use the usual key definition

[Display(Name = “UserId”)]
public string UserId { get; set; }

[Display(Name = “RoleId”)]
public string RoleId { get; set; }

When you run the application you get the error message:

{“error”:”Entity type ‘AspNetUserRoles’ has composite primary key defined with data annotations. To set composite primary key, use fluent API.”}

To declare composite keys, in the fluent API format

In the model declare the keys

public class AspNetUserRoles {

    // Composite primary keys
    // Initialized in ApplicationDbContext.OnModelCreating()
    public object UserId { get; internal set; }
    public object RoleId { get; internal set; }

In the ApplicationDbContext file add the lines to the OnModelCreating(ModelBuilder builder) method

// Composite primary key
builder.Entity().HasKey(table => new {



Generate SQL script from Entity Framework migration script

It is not recommended to execute Entity Framework migration scripts in production, It is important that you execute all SQL steps manually on the production database section-by-section to immediately see the result and be able to recover in case a destructive action goes wrong.

The Visual Studio .NET application templates contain Entity Framework migration scripts to set up your local database to match the sample code. To generate the SQL script you can execute by hand on the production database

Install the EF Core .NET Command-line Tools

  1. Open a command window in the folder of the project that contains the database access code
  2. In the command line execute
    dotnet add package Microsoft.EntityFrameworkCore.Design
    dotnet restore
  3. Test the dotnet ef installation with
    dotnet ef


Script the .NET Entity Framework migrations

  1. Open a command window in the folder of the project that contains the database access code
  2. In the command line execute
    1. To generate the SQL script to bring the current development database to the scripted configuration state, use the –idempotent option.
      (Generating idempotent scripts for migration is not currently supported by MySql)

      dotnet ef migrations script --idempotent --output "script.sql" --context MY_DBCONTEXT
    2. To generate the SQL script based on the entire migration script to update the production database to match the template after you have updated the development database
      dotnet ef migrations script --output "script.sql" --context MY_DBCONTEXT