ASP.NET Core Blazor with Entity Framework Core (EF Core)

This article explains how to use Entity Framework Core (EF Core) in server-side Blazor apps.

Server-side Blazor is a stateful app framework. The app maintains an ongoing connection to the server, and the user's state is held in the server's memory in a circuit. One example of user state is data held in dependency injection (DI) service instances that are scoped to the circuit. The unique application model that Blazor provides requires a special approach to use Entity Framework Core.

Note

This article addresses EF Core in server-side Blazor apps. Blazor WebAssembly apps run in a WebAssembly sandbox that prevents most direct database connections. Running EF Core in Blazor WebAssembly is beyond the scope of this article.

This guidance applies to components that adopt interactive server-side rendering (interactive SSR) in a Blazor Web App.

Secure authentication flow required for production apps

This article uses a local database that doesn't require user authentication. Production apps should use the most secure authentication flow available. For more information on authentication for deployed test and production Blazor apps, see the articles in the Blazor Security and Identity node.

For Microsoft Azure services, we recommend using managed identities. Managed identities securely authenticate to Azure services without storing credentials in app code. For more information, see the following resources:

• What are managed identities for Azure resources? (Microsoft Entra documentation)
• Azure services documentation
  • Managed identities in Microsoft Entra for Azure SQL
  • How to use managed identities for App Service and Azure Functions

Sample app

The sample app was built as a reference for server-side Blazor apps that use EF Core. The sample app includes a grid with sorting and filtering, delete, add, and update operations.

The sample demonstrates use of EF Core to handle optimistic concurrency. However, native database-generated concurrency tokens aren't supported for SQLite databases, which is the database provider for the sample app. To demonstrate concurrency with the sample app, adopt a different database provider that supports database-generated concurrency tokens (for example, the SQL Server provider).

View or download sample code (how to download): Select the folder that matches the version of .NET that you're adopting. Within the version folder, access the sample named BlazorWebAppEFCore.

The sample uses a local SQLite database so that it can be used on any platform. The sample also configures database logging to show the SQL queries that are generated. This is configured in appsettings.Development.json:

{
  "DetailedErrors": true,
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning",
      "Microsoft.Hosting.Lifetime": "Information",
      "Microsoft.EntityFrameworkCore.Database.Command": "Information"
    }
  }
}

The grid, add, and view components use the "context-per-operation" pattern, where a context is created for each operation. The edit component uses the "context-per-component" pattern, where a context is created for each component.

Note

Some of the code examples in this topic require namespaces and services that aren't shown. To inspect the fully working code, including the required @using and @inject directives for Razor examples, see the sample app.

Build a Blazor movie database app tutorial

For a tutorial experience building an app that uses EF Core to work with a database, see Build a Blazor movie database app (Overview). The tutorial shows you how to create a Blazor Web App that can display and manage movies in a movie database.

Database access

EF Core relies on a DbContext as the means to configure database access and act as a unit of work. EF Core provides the AddDbContext extension for ASP.NET Core apps that registers the context as a scoped service. In server-side Blazor apps, scoped service registrations can be problematic because the instance is shared across components within the user's circuit. DbContext isn't thread safe and isn't designed for concurrent use. The existing lifetimes are inappropriate for these reasons:

• Singleton shares state across all users of the app and leads to inappropriate concurrent use.
• Scoped (the default) poses a similar issue between components for the same user.
• Transient results in a new instance per request; but as components can be long-lived, this results in a longer-lived context than may be intended.

The following recommendations are designed to provide a consistent approach to using EF Core in server-side Blazor apps.

• Consider using one context per operation. The context is designed for fast, low overhead instantiation:

  using var context = new MyContext();
  
  return await context.MyEntities.ToListAsync();
  

• Use a flag to prevent multiple concurrent operations:

  if (Loading)
  {
      return;
  }
  
  try
  {
      Loading = true;
  
      ...
  }
  finally
  {
      Loading = false;
  }
  

  Place operations after the Loading = true; line in the try block.

  Thread safety isn't a concern, so loading logic doesn't require locking database records. The loading logic is used to disable UI controls so that users don't inadvertently select buttons or update fields while data is fetched.

• If there's any chance that multiple threads may access the same code block, inject a factory and make a new instance per operation. Otherwise, injecting and using the context is usually sufficient.

• For longer-lived operations that take advantage of EF Core's change tracking or concurrency control, scope the context to the lifetime of the component.

New DbContext instances

The fastest way to create a new DbContext instance is by using new to create a new instance. However, there are scenarios that require resolving additional dependencies:

• Using DbContextOptions to configure the context.
• Using a connection string per DbContext, such as when you use ASP.NET Core's Identity model. For more information, see Multi-tenancy (EF Core documentation).

Warning

Don't store app secrets, connection strings, credentials, passwords, personal identification numbers (PINs), private C#/.NET code, or private keys/tokens in client-side code, which is always insecure. In test/staging and production environments, server-side Blazor code and web APIs should use secure authentication flows that avoid maintaining credentials within project code or configuration files. Outside of local development testing, we recommend avoiding the use of environment variables to store sensitive data, as environment variables aren't the most secure approach. For local development testing, the Secret Manager tool is recommended for securing sensitive data. For more information, see Securely maintain sensitive data and credentials.

The recommended approach to create a new DbContext with dependencies is to use a factory. EF Core 5.0 or later provides a built-in factory for creating new contexts.

The following example configures SQLite and enables data logging. The code uses an extension method (AddDbContextFactory) to configure the database factory for DI and provide default options:

builder.Services.AddDbContextFactory<ContactContext>(opt =>
    opt.UseSqlite($"Data Source={nameof(ContactContext.ContactsDb)}.db"));

The factory is injected into components and used to create new DbContext instances.

In the home page of the sample app, IDbContextFactory<ContactContext> is injected into the component:

@inject IDbContextFactory<ContactContext> DbFactory

A DbContext is created using the factory (DbFactory) to delete a contact in the DeleteContactAsync method:

private async Task DeleteContactAsync()
{
    using var context = DbFactory.CreateDbContext();
    Filters.Loading = true;

    if (Wrapper is not null && context.Contacts is not null)
    {
        var contact = await context.Contacts
            .FirstAsync(c => c.Id == Wrapper.DeleteRequestId);

        if (contact is not null)
        {
            context.Contacts?.Remove(contact);
            await context.SaveChangesAsync();
        }
    }

    Filters.Loading = false;

    await ReloadAsync();
}

Note

Filters is an injected IContactFilters, and Wrapper is a component reference to the GridWrapper component. See the Home component (Components/Pages/Home.razor) in the sample app.

Scope to the component lifetime

You may wish to create a DbContext that exists for the lifetime of a component. This allows you to use it as a unit of work and take advantage of built-in features, such as change tracking and concurrency resolution.

You can use the factory to create a context and track it for the lifetime of the component. First, implement IDisposable and inject the factory as shown in the EditContact component (Components/Pages/EditContact.razor):

@implements IDisposable
@inject IDbContextFactory<ContactContext> DbFactory

The sample app ensures the context is disposed when the component is disposed:

public void Dispose() => Context?.Dispose();

Finally, OnInitializedAsync is overridden to create a new context. In the sample app, OnInitializedAsync loads the contact in the same method:

protected override async Task OnInitializedAsync()
{
    Busy = true;

    try
    {
        Context = DbFactory.CreateDbContext();

        if (Context is not null && Context.Contacts is not null)
        {
            var contact = await Context.Contacts.SingleOrDefaultAsync(c => c.Id == ContactId);

            if (contact is not null)
            {
                Contact = contact;
            }
        }
    }
    finally
    {
        Busy = false;
    }
}

Enable sensitive data logging

EnableSensitiveDataLogging includes application data in exception messages and framework logging. The logged data can include the values assigned to properties of entity instances and parameter values for commands sent to the database. Logging data with EnableSensitiveDataLogging is a security risk, as it may expose passwords and other Personally Identifiable Information (PII) when it logs SQL statements executed against the database.

We recommend only enabling EnableSensitiveDataLogging for development and testing:

#if DEBUG
    services.AddDbContextFactory<ContactContext>(opt =>
        opt.UseSqlite($"Data Source={nameof(ContactContext.ContactsDb)}.db")
        .EnableSensitiveDataLogging());
#else
    services.AddDbContextFactory<ContactContext>(opt =>
        opt.UseSqlite($"Data Source={nameof(ContactContext.ContactsDb)}.db"));
#endif

Additional resources

• EF Core documentation
• Blazor samples GitHub repository (dotnet/blazor-samples)
• Blazor Security and Identity node articles