Part 5, work with a database in an ASP.NET Core MVC app

By Rick Anderson and Jon P Smith.

The MvcMovieContext 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 the Program.cs file:

C#

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddDbContext<MvcMovieContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("MvcMovieContext") ?? throw new InvalidOperationException("Connection string 'MvcMovieContext' not found.")));

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

JSON

"ConnectionStrings": {
  "MvcMovieContext": "Server=(localdb)\\mssqllocaldb;Database=MvcMovieContext-4ebefa10-de29-4dea-b2ad-8a8dc6bcf374;Trusted_Connection=True;MultipleActiveResultSets=true"
}

C#

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddDbContext<MvcMovieContext>(options =>
    options.UseSqlite(builder.Configuration.GetConnectionString("MvcMovieContext")));

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

JSON

"ConnectionStrings": {
  "MvcMovieContext": "Data Source=MvcMovie.db"
}

Hoiatus

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.

SQL Server Express LocalDB

LocalDB:

• Is a lightweight version of the SQL Server Express Database Engine, installed by default with Visual Studio.
• Starts on demand by using a connection string.
• Is targeted for program development. It runs in user mode, so there's no complex configuration.
• By default creates .mdf files in the C:/Users/{user} directory.

Examine the database

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

Right-click on the Movie table (dbo.Movie) > View Designer

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

Right-click on the Movie table > View Data

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.

Märkus

For this tutorial you use the Entity Framework Core migrations feature 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, you drop and re-create the database.

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. Replace the generated code with the following:

C#

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using MvcMovie.Data;
using System;
using System.Linq;

namespace MvcMovie.Models;

public static class SeedData
{
    public static void Initialize(IServiceProvider serviceProvider)
    {
        using (var context = new MvcMovieContext(
            serviceProvider.GetRequiredService<
                DbContextOptions<MvcMovieContext>>()))
        {
            // 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.

C#

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

Add the seed initializer

Replace the contents of Program.cs with the following code. The new code is highlighted.

C#

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using MvcMovie.Data;
using MvcMovie.Models;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddDbContext<MvcMovieContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("MvcMovieContext") ?? throw new InvalidOperationException("Connection string 'MvcMovieContext' not found.")));

// Add services to the container.
builder.Services.AddControllersWithViews();

var app = builder.Build();

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

    SeedData.Initialize(services);
}

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Home/Error");
    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
    app.UseHsts();
}

app.UseHttpsRedirection();

app.UseRouting();

app.UseAuthorization();

app.MapStaticAssets();

app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");

app.Run();

Delete all the records in the database. You can do this with the delete links in the browser or from SSOX.

Test the app. Force the app to initialize, calling the code in the Program.cs file, so the seed method runs. To force initialization, close the command prompt window that Visual Studio opened, and restart by pressing Ctrl+F5.

Update Program.cs with the following highlighted code:

C#

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

builder.Services.AddDbContext<MvcMovieContext>(options =>
    options.UseSqlite(builder.Configuration.GetConnectionString("MvcMovieContext")));

// Add services to the container.
builder.Services.AddControllersWithViews();

var app = builder.Build();

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

    SeedData.Initialize(services);
}

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Home/Error");
    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
    app.UseHsts();
}

app.UseHttpsRedirection();

app.UseRouting();

app.UseAuthorization();

app.MapStaticAssets();

app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");

app.Run();

Delete all the records in the database.

Test the app. Stop it and restart it so the SeedData.Initialize method runs and seeds the database.

The app shows the seeded data.

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