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

Windows

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

PowerShell

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

macOS

  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"
        }
    }
    
    

 

Enable .NET Core Entity Framework Linq query execution

When we create a new .NET Core class it only contains the using System; reference.

To enable Linq database queries in a .NET Core project, add using System.Linq;

using System;
using System.Linq;

To enable the usage of .Include() in the Linq queries, add

using Microsoft.EntityFrameworkCore;

 

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" >
</form>

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:

cd MY_CLASS_LIBRARY_DIRECTORY
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:
/usr/local/share/dotnet/
– Installing .NET Core prerequisites might help resolve this problem:
http://go.microsoft.com/fwlink/?LinkID=798306&clcid=0x409
– The .NET Core framework and SDK can be installed from:
https://aka.ms/dotnet-download
– 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.

<PropertyGroup>
...
<GenerateRuntimeConfigurationFiles>True</GenerateRuntimeConfigurationFiles>
...
</PropertyGroup>

 

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=6.9.10.0, 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

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

[Key]
[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 {
   table.UserId,
   table.RoleId
});

 

 

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

 

 

DbUpdateConcurrencyException: Database operation expected to affect 1 row(s) but actually affected 0 row(s). Data may have been modified or deleted since entities were loaded.

The .NET Core Entity framework makes database access easy. When you auto-generate a Razor page in a .NET web application to edit a data row, the scaffolding places controls on the page for every column.

There are columns in most of the tables that we don’t want to display or edit, like keys, checksums, password hashes. If column values are missing during database update, the error is thrown:

A database operation failed while processing the request.
DbUpdateConcurrencyException: Database operation expected to affect 1 row(s) but actually affected 0 row(s). Data may have been modified or deleted since entities were loaded. See http://go.microsoft.com/fwlink/?LinkId=527962 for information on understanding and handling optimistic concurrency exceptions.

When the edit page is displayed, all values of the row are passed to the page in the Model. When the user clicks the Save button the model is sent back to the server, and the OnPostAsync() method saves the values to the database. The values that we don’t display or store otherwise on the web page are not retained in the browser, and not passed back to the server. To keep the not displayed values, add hidden attributes to the page. The primary key of the row is automatically added, and based on that create hidden attributes for the rest of the not displayed columns.

 <form method="post">
 <div asp-validation-summary="ModelOnly" class="text-danger"></div>
 <input type="hidden" asp-for="ApplicationUser.Id" />
 <input type="hidden" asp-for="ApplicationUser.AccessFailedCount" />
 <input type="hidden" asp-for="ApplicationUser.ConcurrencyStamp" />
 <input type="hidden" asp-for="ApplicationUser.NormalizedEmail" />
 <input type="hidden" asp-for="ApplicationUser.NormalizedUserName" />
 <input type="hidden" asp-for="ApplicationUser.PasswordHash" />
 <input type="hidden" asp-for="ApplicationUser.SecurityStamp" />
 <input type="hidden" asp-for="ApplicationUser.UserName" />