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title author description monikerRange ms.author ms.custom ms.date uid
ASP.NET Core Blazor with Entity Framework Core (EF Core)
guardrex
Learn how to use Entity Framework Core (EF Core) in Blazor apps.
>= aspnetcore-3.1
jeliknes
mvc
02/09/2024
blazor/blazor-ef-core

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

[!INCLUDE]

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.

:::moniker range=">= aspnetcore-8.0"

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

:::moniker-end

:::moniker range="< aspnetcore-8.0"

This guidance applies to the Server project of a hosted Blazor WebAssembly solution or a Blazor Server app.

:::moniker-end

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.

View or download sample code (how to download)

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:

:::moniker range=">= aspnetcore-8.0"

:::code language="json" source="~/../blazor-samples/8.0/BlazorWebAppEFCore/appsettings.Development.json" highlight="8":::

:::moniker-end

:::moniker range=">= aspnetcore-7.0 < aspnetcore-8.0"

:::code language="json" source="~/../blazor-samples/7.0/BlazorServerEFCoreSample/appsettings.Development.json" highlight="8":::

:::moniker-end

:::moniker range=">= aspnetcore-6.0 < aspnetcore-7.0"

:::code language="json" source="~/../blazor-samples/6.0/BlazorServerEFCoreSample/appsettings.Development.json" highlight="8":::

:::moniker-end

:::moniker range=">= aspnetcore-5.0 < aspnetcore-6.0"

:::code language="json" source="~/../blazor-samples/5.0/BlazorServerEFCoreSample/appsettings.Development.json" highlight="8":::

:::moniker-end

:::moniker range="< aspnetcore-5.0"

:::code language="json" source="~/../blazor-samples/3.1/BlazorServerEFCoreSample/appsettings.Development.json" highlight="8":::

:::moniker-end

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.

Database access

EF Core relies on a xref:Microsoft.EntityFrameworkCore.DbContext as the means to configure database access and act as a unit of work. EF Core provides the xref:Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.AddDbContext%2A extension for ASP.NET Core apps that registers the context as a scoped service by default. In server-side Blazor apps, scoped service registrations can be problematic because the instance is shared across components within the user's circuit. xref:Microsoft.EntityFrameworkCore.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.

  • By default, 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.

    Loading logic doesn't require locking database records because thread safety isn't a concern. 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 xref:Microsoft.EntityFrameworkCore.DbContext instance is by using new to create a new instance. However, there are scenarios that require resolving additional dependencies:

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

:::moniker range="< aspnetcore-5.0"

:::code language="csharp" source="~/../blazor-samples/3.1/BlazorServerEFCoreSample/Data/DbContextFactory.cs":::

In the preceding factory:

  • xref:Microsoft.Extensions.DependencyInjection.ActivatorUtilities.CreateInstance%2A?displayProperty=nameWithType satisfies any dependencies via the service provider.
  • IDbContextFactory is available in EF Core ASP.NET Core 5.0 or later, so the interface is implemented in the sample app for ASP.NET Core 3.x.

:::moniker-end

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:

:::moniker range=">= aspnetcore-8.0"

:::code language="csharp" source="~/../blazor-samples/8.0/BlazorWebAppEFCore/Program.cs" id="snippet1":::

:::moniker-end

:::moniker range=">= aspnetcore-7.0 < aspnetcore-8.0"

:::code language="csharp" source="~/../blazor-samples/7.0/BlazorServerEFCoreSample/Program.cs" id="snippet1":::

:::moniker-end

:::moniker range=">= aspnetcore-6.0 < aspnetcore-7.0"

:::code language="csharp" source="~/../blazor-samples/6.0/BlazorServerEFCoreSample/Program.cs" id="snippet1":::

:::moniker-end

:::moniker range=">= aspnetcore-5.0 < aspnetcore-6.0"

:::code language="csharp" source="~/../blazor-samples/5.0/BlazorServerEFCoreSample/Startup.cs" id="snippet1":::

:::moniker-end

:::moniker range="< aspnetcore-5.0"

:::code language="csharp" source="~/../blazor-samples/3.1/BlazorServerEFCoreSample/Startup.cs" id="snippet1":::

:::moniker-end

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:

:::moniker range=">= aspnetcore-8.0"

:::code language="razor" source="~/../blazor-samples/8.0/BlazorWebAppEFCore/Components/Pages/Home.razor" id="snippet1":::

:::moniker-end

:::moniker range=">= aspnetcore-7.0 < aspnetcore-8.0"

:::code language="razor" source="~/../blazor-samples/7.0/BlazorServerEFCoreSample/Pages/Index.razor" id="snippet1":::

:::moniker-end

:::moniker range=">= aspnetcore-6.0 < aspnetcore-7.0"

:::code language="razor" source="~/../blazor-samples/6.0/BlazorServerEFCoreSample/Pages/Index.razor" id="snippet1":::

:::moniker-end

:::moniker range=">= aspnetcore-5.0 < aspnetcore-6.0"

:::code language="razor" source="~/../blazor-samples/5.0/BlazorServerEFCoreSample/Pages/Index.razor" id="snippet1":::

:::moniker-end

:::moniker range="< aspnetcore-5.0"

:::code language="razor" source="~/../blazor-samples/3.1/BlazorServerEFCoreSample/Pages/Index.razor" id="snippet1":::

:::moniker-end

:::moniker range=">= aspnetcore-8.0"

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.

:::moniker-end

:::moniker range="< aspnetcore-8.0"

Note

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

:::moniker-end

Scope to the component lifetime

You may wish to create a xref:Microsoft.EntityFrameworkCore.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.

:::moniker range=">= aspnetcore-8.0"

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

:::moniker-end

:::moniker range="< aspnetcore-8.0"

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

:::moniker-end

@implements IDisposable
@inject IDbContextFactory<ContactContext> DbFactory

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

:::moniker range=">= aspnetcore-8.0"

:::code language="csharp" source="~/../blazor-samples/8.0/BlazorWebAppEFCore/Components/Pages/EditContact.razor" id="snippet1":::

:::moniker-end

:::moniker range=">= aspnetcore-7.0 < aspnetcore-8.0"

:::code language="csharp" source="~/../blazor-samples/7.0/BlazorServerEFCoreSample/Pages/EditContact.razor" id="snippet1":::

:::moniker-end

:::moniker range=">= aspnetcore-6.0 < aspnetcore-7.0"

:::code language="csharp" source="~/../blazor-samples/6.0/BlazorServerEFCoreSample/Pages/EditContact.razor" id="snippet1":::

:::moniker-end

:::moniker range=">= aspnetcore-5.0 < aspnetcore-6.0"

:::code language="csharp" source="~/../blazor-samples/5.0/BlazorServerEFCoreSample/Pages/EditContact.razor" id="snippet1":::

:::moniker-end

:::moniker range="< aspnetcore-5.0"

:::code language="csharp" source="~/../blazor-samples/3.1/BlazorServerEFCoreSample/Pages/EditContact.razor" id="snippet1":::

:::moniker-end

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

:::moniker range=">= aspnetcore-8.0"

:::code language="csharp" source="~/../blazor-samples/8.0/BlazorWebAppEFCore/Components/Pages/EditContact.razor" id="snippet2":::

:::moniker-end

:::moniker range=">= aspnetcore-7.0 < aspnetcore-8.0"

:::code language="csharp" source="~/../blazor-samples/7.0/BlazorServerEFCoreSample/Pages/EditContact.razor" id="snippet2":::

:::moniker-end

:::moniker range=">= aspnetcore-6.0 < aspnetcore-7.0"

:::code language="csharp" source="~/../blazor-samples/6.0/BlazorServerEFCoreSample/Pages/EditContact.razor" id="snippet2":::

:::moniker-end

:::moniker range=">= aspnetcore-5.0 < aspnetcore-6.0"

:::code language="csharp" source="~/../blazor-samples/5.0/BlazorServerEFCoreSample/Pages/EditContact.razor" id="snippet2":::

:::moniker-end

:::moniker range="< aspnetcore-5.0"

:::code language="csharp" source="~/../blazor-samples/3.1/BlazorServerEFCoreSample/Pages/EditContact.razor" id="snippet2":::

In the preceding example:

  • When Busy is set to true, asynchronous operations may begin. When Busy is set back to false, asynchronous operations should be finished.
  • Place additional error handling logic in a catch block.

:::moniker-end

Enable sensitive data logging

xref:Microsoft.EntityFrameworkCore.DbContextOptionsBuilder.EnableSensitiveDataLogging%2A 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 xref:Microsoft.EntityFrameworkCore.DbContextOptionsBuilder.EnableSensitiveDataLogging%2A 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 xref:Microsoft.EntityFrameworkCore.DbContextOptionsBuilder.EnableSensitiveDataLogging%2A 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