No connection string named ‘…’ could be found in the application config file.

Two-tier applications separate the presentation layer and the data layer, and all database access related objects are located in the data-tier.

When the application runs, the config file of the main project is read. In web applications, it is the web.config, in console applications the app.config file.

When you get the following runtime exception

Exception thrown: ‘System.InvalidOperationException’ in EntityFramework.dll
An exception of type ‘System.InvalidOperationException’ occurred in EntityFramework.dll but was not handled in user code
No connection string named ‘…Entities’ could be found in the application config file.

 

  1. Copy the connection string from the app.config file of the data-tier to the main project’s config file.
 <add name="USC_SocialMediaMSSQLEntities" connectionString="metadata=res://*/USC_SocialMedia_MSSQL.csdl|res://*/USC_SocialMedia_MSSQL.ssdl|res://*/USC_SocialMedia_MSSQL.msl;provider=System.Data.SqlClient;provider connection string=&quot;data source=MY_SERVER;initial catalog=MY_DATABASE;user id=MY_USER;password=MY_PASWORD;MultipleActiveResultSets=True;App=EntityFramework&quot;" providerName="System.Data.EntityClient" />

2. This is a sample data access class in the data-layer to read data from the aspNetRoles table.

using System.Data.Entity;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SocialMedia_Data {
	public class SocialMediaData {

		private USC_SocialMediaMSSQLEntities _web;

		public SocialMediaData() {

			// Set up the database connections
			_web = new USC_SocialMediaMSSQLEntities();

		}

		/// Returns the list of Roles
		public List GetRoles() {

			IEnumerable foundRoles = from aspNetRoles in _web.AspNetRoles
						 orderby aspNetRoles.DisplayOrder
						 select aspNetRoles;

			if (null == foundRoles || 0 == foundRoles.Count()) {
				return null;
			}

			return foundRoles.ToList();

		}
	}
}

NotSupportedException: Unable to determine the provider name for provider factory of type ‘MySql.Data.MySqlClient.MySqlClientFactory’. Make sure that the ADO.NET provider is installed or registered in the application config

In a two-tier web application, the data layer is in a separate project. This allows better separation between the presentation layer and the data layer. This way you can reuse the data project in another application that targets the same database.

To access a MySql database you need to add the MySql.Data and MySql.Data.Entity NuGet packages to the data project.

When you develop a two-tier application that targets a MySql database you may get the runtime error

NotSupportedException: Unable to determine the provider name for provider factory of type ‘MySql.Data.MySqlClient.MySqlClientFactory’. Make sure that the ADO.NET provider is installed or registered in the application config.

Even if all database interaction is handled in the data project, and you added the MySql NuGet packages to it, you need to add the MySql.Data and MySql.Data.Entity NuGet packages to the web project too, because the Web.config file contains the connection string that includes the reference to MySql.Data.MySqlClient.

<add name="MY_CONNECTION_NAME" providerName="MySql.Data.MySqlClient" connectionString="server=localhost;port=3306;database=MY_DATABASE;uid=MY_USERNAME;password=MY_PASSWORD" />

At the time of writing do not use version 6.10.6.0 of the packages, it causes the error

Exception thrown: ‘System.TypeLoadException’ in mscorlib.dll
An exception of type ‘System.TypeLoadException’ occurred in mscorlib.dll but was not handled in user code
Inheritance security rules violated by type: ‘MySql.Data.MySqlClient.MySqlProviderServices’. Derived types must either match the security accessibility of the base type or be less accessible.

Until a new, corrected version is published, install version 6.9.11.0 of both packages in both projects.

For more information on how to connect to a MySql database from Visual Studio see Connect to a MySQL database from Visual Studio 2017

 

 

Create an ASP.NET MVC 5 Web Application with user authentication

To create a new ASP .NET MVC web application that contains user authentication code

  1. In the File menu of Visual Studio select New, Project
  2. On the left select Visual C#, Web, and in the middle select ASP.NET Web Application (.NET Framework)
  3. Enter the Name, select the solution folder location and click OK. The solution name will automatically match the value of the Name field.
  4. Select MVC and click the Change Authentication button
  5. To use your database for authentication select Individual User Accounts
  6. Make sure the correct authentication is selected and click OK

This ASP.NET MVC 5 web application automatically creates an SQL Express internal database in the App_Data directory of the application when you register the first user.

  1. Start the application
  2. Click Register in the menu of the web application
  3. Register a user

To use an external database for user authentication, see the next post at Configure the ASP.NET MVC 5 web application to use an external database for user authentication

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" />

Connect to a MySQL database from Visual Studio 2017

As of today weI can connect to a MySQL database, but cannot generate the Entity Data Model from a MySQL database in Visual Studio 2017

To access a MySQL database from Visual Studio 2017

IMPORTANT: First install MySQL for Visual Studio, and after that install MySQL Connector/Net.

If MySQL Connector/Net is already installed on your workstation, uninstall it before installing MySQL for Visual Studio and reinstall MySQL Connector/Net.

Install MySQL for Visual Studio

Available version information is at https://dev.mysql.com/doc/visual-studio/en/visual-studio-intro.html

  1. Close all instances of Visual Studio,
  2. Download the installer from https://dev.mysql.com/downloads/windows/visualstudio/
  3. Start the installer
  4. Click the Complete button,
  5. If you select Typical, make sure the Visual Studio 2017 components are selected

 

Install the MySql Connector/Net the fully-managed ADO.NET driver for MySQL

  1. Download the installer from https://dev.mysql.com/downloads/connector/net/
  2. Download version 6.9.10, because version 6.10.5 throws the

    Inheritance security rules violated by type: ‘MySql.Data.Entity.MySqlEFConfiguration’. Derived types must either match the security accessibility of the base type or be less accessible

    error. More info at https://stackoverflow.com/questions/47227495/inheritance-security-rules-violated-by-type-mysql-data-entity-mysqlefconfigura

  3. Select version 6.9.10, your operating system and click the Download button
  4. If you don’t want to create an Oracle account, click the No thanks… link
  5. Start the downloaded installer
  6. Click the Complete button

Install the NuGet packages

Make sure to install the same version of the NuGet packages as the MySql Connector/Net

Generate Entity Framework Entity Data Model in Visual Studio 2017

Visual Studio 2017 has many project type options, and not all of them support the Entity Framework user interface to generate the Entity Framework Data Model (EDMX) file. If you create an ASP.NET Web Application(.NET Framework) you can add the EDMX file to it. The .NET Core projects do not support the Entity Framework Data Model creation.

For more complex web applications it is good practice to separate the data access layer from the presentation layer. You can even reference the data access project from another solution if that also needs access to the same data.

To be able to use the graphical user interface to generate the Entity Framework Entity Data Model

  1. Add a new Class Library (.NET Framework) type project to the solution,
  2. Right-click the new project and select Add -> New Item
  3. In the Data section select the ADO.NET Entity Data Model
  4. Select EF Designer from database
  5. Continue the process to create the database connection and generate the data model.

Generate the Entity Classes

  1. Open the EDMX file
  2. Right-click the background and select Add Code Generation Item
  3. Select the latest EF DbContext Generator
  4. When the classes have been generated, close the solution and open it again, otherwise, the newly created classes cannot be referenced.

{“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" />

 

 

 

java.lang.NoClassDefFoundError, java.lang.ClassNotFoundException

When you add a dependency reference to a Java project, it may compile without any errors, but runtime you may get an error message similar to this:

HTTP Status 500 – Internal Server Error

Type Exception Report

Message An exception occurred processing JSP page [/index.jsp] at line [1]

Description The server encountered an unexpected condition that prevented it from fulfilling the request.

Exception

org.apache.jasper.JasperException: An exception occurred processing JSP page [/index.jsp] at line [1]

1: <jsp:forward page=”….html” />

Root Cause

javax.servlet.ServletException: Servlet.init() for servlet [spring] threw exception…

Root Cause

java.lang.NoClassDefFoundError: org/springframework/core/env/PropertySource…

Root Cause

java.lang.ClassNotFoundException: org.springframework.core.env.PropertySource…

If the newly added dependency also depends on another package, and that package is already in the pom.xml file, NetBeans will not show an error during build.

If the newly added dependency was recently introduced, and the version of the package already included in the pom.xml file,  references an earlier version, the runtime error will occur.

For example org.springframework.web.bind.annotation.GetMapping was introduced in Spring Web 4.0

If your pom.xml file already contains the reference to spring-web or spring-webmvc version 3, your application will fail runtime.

<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>3.0.5.RELEASE</version>
</dependency>

In your web browser navigate to the Maven repository at https://mvnrepository.com/artifact/org.springframework and search for the spring-web and spring-webmvc packages. Get the latest stable version numbers and update your pom.xml file.

 <dependency>
   <groupId>org.springframework</groupId>
   <artifactId>spring-webmvc</artifactId>
   <version>5.0.2.RELEASE</version>
 </dependency>