Part 4 of tutorial series on Razor Pages

By Joe Audette

The RazorPagesMovieContext object handles the task of connecting to the database and mapping Movie objects to database records. The database context is registered with the Dependency Injection container in Program.cs:

Visual Studio

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using RazorPagesMovie.Data;
var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddRazorPages();
builder.Services.AddDbContext<RazorPagesMovieContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("RazorPagesMovieContext") ?? throw new InvalidOperationException("Connection string 'RazorPagesMovieContext' not found.")));

Visual Studio Code

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using RazorPagesMovie.Data;
var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddRazorPages();
builder.Services.AddDbContext<RazorPagesMovieContext>(options =>
    options.UseSqlite(builder.Configuration.GetConnectionString("RazorPagesMovieContext") ?? throw new InvalidOperationException("Connection string 'RazorPagesMovieContext' not found.")));

var app = builder.Build();

The ASP.NET Core Configuration system reads the ConnectionString key. For local development, configuration gets the connection string from the appsettings.json file.

Visual Studio

The generated connection string is similar to the following JSON:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "ConnectionStrings": {
    "RazorPagesMovieContext": "Server=(localdb)\\mssqllocaldb;Database=RazorPagesMovieContext-f2e0482c-952d-4b1c-afe9-a1a3dfe52e55;Trusted_Connection=True;MultipleActiveResultSets=true"
  }
}

Visual Studio Code

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "ConnectionStrings": {
    "RazorPagesMovieContext": "Data Source=RazorPagesMovie.Data.db"
  }
}

Warning

This article uses a local database that doesn't require the user to be authenticated. Production apps should use the most secure authentication flow available. For more information on authentication for deployed test and production apps, see Secure authentication flows.

Visual Studio

SQL Server Express LocalDB

LocalDB is a lightweight version of the SQL Server Express database engine that's targeted for program development. LocalDB starts on demand and runs in user mode, so there's no complex configuration. By default, LocalDB database creates *.mdf files in the C:\Users\<user>\ directory.

1. From the View menu, open SQL Server Object Explorer (SSOX).

   

2. Right-click on the Movie table and select View Designer:

   

   

   Note the key icon next to ID. By default, EF creates a property named ID for the primary key.

3. Right-click on the Movie table and select View Data:

   

Visual Studio Code

SQLite

The SQLite website states:

SQLite is a self-contained, high-reliability, embedded, full-featured, public-domain, SQL database engine. SQLite is the most used database engine in the world.

There are many third-party tools you can download to manage and view a SQLite database. The image below is from DB Browser for SQLite. If you have a favorite SQLite tool, leave a comment on what you like about it.

Note

For this tutorial, the Entity Framework Core migrations feature is used where possible. Migrations updates the database schema to match changes in the data model. However, migrations can only do the kinds of changes that the EF Core provider supports, and the SQLite provider's capabilities are limited. For example, adding a column is supported, but removing or changing a column is not supported. If a migration is created to remove or change a column, the ef migrations add command succeeds but the ef database update command fails. Due to these limitations, this tutorial doesn't use migrations for SQLite schema changes. Instead, when the schema changes, the database is dropped and re-created.

The workaround for the SQLite limitations is to manually write migrations code to perform a table rebuild when something in the table changes. A table rebuild involves:

• Creating a new table.
• Copying data from the old table to the new table.
• Dropping the old table.
• Renaming the new table.

For more information, see the following resources:

• SQLite EF Core Database Provider Limitations
• Customize migration code
• Data seeding
• SQLite ALTER TABLE statement

Seed the database

Create a new class named SeedData in the Models folder with the following code:

using Microsoft.EntityFrameworkCore;
using RazorPagesMovie.Data;

namespace RazorPagesMovie.Models;

public static class SeedData
{
    public static void Initialize(IServiceProvider serviceProvider)
    {
        using (var context = new RazorPagesMovieContext(
            serviceProvider.GetRequiredService<
                DbContextOptions<RazorPagesMovieContext>>()))
        {
            if (context == null || context.Movie == null)
            {
                throw new ArgumentNullException("Null RazorPagesMovieContext");
            }

            // Look for any movies.
            if (context.Movie.Any())
            {
                return;   // DB has been seeded
            }

            context.Movie.AddRange(
                new Movie
                {
                    Title = "When Harry Met Sally",
                    ReleaseDate = DateTime.Parse("1989-2-12"),
                    Genre = "Romantic Comedy",
                    Price = 7.99M
                },

                new Movie
                {
                    Title = "Ghostbusters ",
                    ReleaseDate = DateTime.Parse("1984-3-13"),
                    Genre = "Comedy",
                    Price = 8.99M
                },

                new Movie
                {
                    Title = "Ghostbusters 2",
                    ReleaseDate = DateTime.Parse("1986-2-23"),
                    Genre = "Comedy",
                    Price = 9.99M
                },

                new Movie
                {
                    Title = "Rio Bravo",
                    ReleaseDate = DateTime.Parse("1959-4-15"),
                    Genre = "Western",
                    Price = 3.99M
                }
            );
            context.SaveChanges();
        }
    }
}

If there are any movies in the database, the seed initializer returns and no movies are added.

if (context.Movie.Any())
{
    return;
}

Add the seed initializer

Update the Program.cs with the following highlighted code:

Visual Studio

using Microsoft.EntityFrameworkCore;
using RazorPagesMovie.Data;
using RazorPagesMovie.Models;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddRazorPages();
builder.Services.AddDbContext<RazorPagesMovieContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("RazorPagesMovieContext") ?? throw new InvalidOperationException("Connection string 'RazorPagesMovieContext' not found.")));

var app = builder.Build();

using (var scope = app.Services.CreateScope())
{
    var services = scope.ServiceProvider;

    SeedData.Initialize(services);
}

if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error");
    app.UseHsts();
}

app.UseHttpsRedirection();

app.UseRouting();

app.UseAuthorization();

app.MapStaticAssets();
app.MapRazorPages();

app.Run();

Visual Studio Code

using Microsoft.EntityFrameworkCore;
using RazorPagesMovie.Data;
using RazorPagesMovie.Models;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddRazorPages();
builder.Services.AddDbContext<RazorPagesMovieContext>(options =>
    options.UseSqlite(builder.Configuration.GetConnectionString("RazorPagesMovieContext") ?? throw new InvalidOperationException("Connection string 'RazorPagesMovieContext' not found.")));

var app = builder.Build();

using (var scope = app.Services.CreateScope())
{
    var services = scope.ServiceProvider;

    SeedData.Initialize(services);
}

if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error");
    app.UseHsts();
}

app.UseHttpsRedirection();

app.UseRouting();

app.UseAuthorization();

app.MapStaticAssets();
app.MapRazorPages();

app.Run();

In the previous code, Program.cs has been modified to do the following:

• Get a database context instance from the dependency injection (DI) container.
• Call the seedData.Initialize method, passing to it the database context instance.
• Dispose the context when the seed method completes. The using statement ensures the context is disposed.

The following exception occurs when Update-Database has not been run:

SqlException: Cannot open database "RazorPagesMovieContext-" requested by the login. The login failed. Login failed for user 'user name'.

Test the app

Delete all the records in the database so the seed method will run. Stop and start the app to seed the database. If the database isn't seeded, put a breakpoint on if (context.Movie.Any()) and step through the code.

The app shows the seeded data:

Next steps

Previous: Scaffolded Razor Pages Next: Update the pages