Connect to a database

There are a few things you need to use Entity Framework Core to connect to a database. Since you used dotnet new and the MVC + Individual Auth template to set your project, you’ve already got them:

  • The Entity Framework Core packages. These are included by default in all ASP.NET Core projects.

  • A database (naturally). The app.db file in the project root directory is a small SQLite database created for you by dotnet new. SQLite is a lightweight database engine that can run without requiring you to install any extra tools on your machine, so it’s easy and quick to use in development.

  • A database context class. The database context is a C# class that provides an entry point into the database. It’s how your code will interact with the database to read and save items. A basic context class already exists in the Data/ApplicationDbContext.cs file.

  • A connection string. Whether you are connecting to a local file database (like SQLite) or a database hosted elsewhere, you’ll define a string that contains the name or address of the database to connect to. This is already set up for you in the appsettings.json file: the connection string for the SQLite database is DataSource=app.db.

Entity Framework Core uses the database context, together with the connection string, to establish a connection to the database. You need to tell Entity Framework Core which context, connection string, and database provider to use in the ConfigureServices method of the Startup class. Here’s what’s defined for you, thanks to the template:

  1. services.AddDbContext<ApplicationDbContext>(options =>
  2.     options.UseSqlite(Configuration.GetConnectionString("DefaultConnection")));

This code adds the ApplicationDbContext to the service container, and tells Entity Framework Core to use the SQLite database provider, with the connection string from configuration (appsettings.json).

As you can see, dotnet new creates a lot of stuff for you! The database is set up and ready to be used. However, it doesn’t have any tables for storing to-do items. In order to store your TodoItem entities, you’ll need to update the context and migrate the database.