Intercepting saving changes
The .NET framework makes heavy use of a well-known design pattern called Observer. This pattern enables an interested party to register for notifications about a target object. In .NET parlance, this is called events. In this recipe, we will see how we can use events to receive notifications when an entity is about to be saved, and act upon it, including canceling the changes. Let's see how to do it.
Getting ready
We will be using NuGet Package Manager to install the Entity Framework Core 1 package, Microsoft.EntityFrameworkCore. We will also be using a SQL Server database for storing the data, so we will also need Microsoft.EntityFrameworkCore.SqlServer.
Finally, xunit is the package we will be using for the unit tests and dotnet-text-xunit adds tooling support for Visual Studio. Note that the UnitTests project is a .NET Core App 1.0 (netcoreapp1.0), where Microsoft.EntityFrameworkCore.Design is configured as a build dependency and Microsoft.EntityFrameworkCore...
