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Data Models
EF Context Review

In this lesson you learned how to build database models and connect your ASP.NET application to a working database:

  • Models are C# classes that define entity structure. They are defined in the Models/ folder.
  • The connection string is the link from the C# code to the physical database. It’s defined in appsettings.json.
  • Three packages are required to get Entity Framework (EF) running:
    dotnet add package Microsoft.EntityFrameworkCore.SQLite dotnet add package Microsoft.EntityFrameworkCore.Design dotnet add package Microsoft.EntityFrameworkCore.Tools
  • The context is a class that acts as a middle man. It has C# methods that you can call to ask the database to do something useful, like add a record or return all rows in a table. It relies on the connection string in appsettings.json to physically locate the database file. It is defined in the Data/ folder.
  • The EF context is added to the app by editing Startup.ConfigureServices() and adding new functionality in Program.cs (we did that by adding the CreateDBIfNotExists() method).

In Startup.cs:

public void ConfigureServices(IServiceCollection services) { services.AddRazorPages(); services.AddDbContext<CountryContext>(options => options.UseSqlite(Configuration.GetConnectionString("CountryContext"))); }

In Program.cs:

private static void CreateDbIfNotExists(IHost host) { using (var scope = host.Services.CreateScope()) { var services = scope.ServiceProvider; var context = services.GetRequiredService<CountryContext>(); context.Database.EnsureCreated(); } }

Instructions

The completed web app is shown in the text editor.

For each bullet in the list above, try to find the code that corresponds to it.

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