MediatR 14.2.0

MediatR

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Simple mediator implementation in .NET

In-process messaging with no dependencies.

Supports request/response, commands, queries, notifications and events, synchronous and async with intelligent dispatching via C# generic variance.

Examples in the wiki.

Installing MediatR

You should install MediatR with NuGet:

Install-Package MediatR

Or via the .NET Core command line interface:

dotnet add package MediatR

Either commands, from Package Manager Console or .NET Core CLI, will download and install MediatR and all required dependencies.

Using Contracts-Only Package

To reference only the contracts for MediatR, which includes:

  • IRequest (including generic variants)
  • INotification
  • IStreamRequest

Add a package reference to MediatR.Contracts

This package is useful in scenarios where your MediatR contracts are in a separate assembly/project from handlers. Example scenarios include:

  • API contracts
  • GRPC contracts
  • Blazor

Registering with IServiceCollection

MediatR supports Microsoft.Extensions.DependencyInjection.Abstractions directly. To register various MediatR services and handlers:

services.AddMediatR(cfg => cfg.RegisterServicesFromAssemblyContaining<Startup>());

or with an assembly:

services.AddMediatR(cfg => cfg.RegisterServicesFromAssembly(typeof(Startup).Assembly));

This registers:

  • IMediator as transient
  • ISender as transient
  • IPublisher as transient
  • IRequestHandler<,> concrete implementations as transient
  • IRequestHandler<> concrete implementations as transient
  • INotificationHandler<> concrete implementations as transient
  • IStreamRequestHandler<> concrete implementations as transient
  • IRequestExceptionHandler<,,> concrete implementations as transient
  • IRequestExceptionAction<,>) concrete implementations as transient

This also registers open generic implementations for:

  • INotificationHandler<>
  • IRequestExceptionHandler<,,>
  • IRequestExceptionAction<,>

To register behaviors, stream behaviors, pre/post processors:

services.AddMediatR(cfg => {
    cfg.RegisterServicesFromAssembly(typeof(Startup).Assembly);
    cfg.AddBehavior<PingPongBehavior>();
    cfg.AddStreamBehavior<PingPongStreamBehavior>();
    cfg.AddRequestPreProcessor<PingPreProcessor>();
    cfg.AddRequestPostProcessor<PingPongPostProcessor>();
    cfg.AddOpenBehavior(typeof(GenericBehavior<,>));
    });

With additional methods for open generics and overloads for explicit service types.

Setting the license key

You can set the license key when registering MediatR:

services.AddMediatR(cfg => 
{
    cfg.LicenseKey = "<license key here>";
})

Or if not using Microsoft.Extensions.DependencyInjection:

Mediator.LicenseKey = "<license key here>";

[!TIP] The license key does not need to be set on client applications (such as Blazor WASM). Turn off the license warning by configuring logging in your logging start configuration: builder.Logging.AddFilter("LuckyPennySoftware.MediatR.License", LogLevel.None);

Auto-discovery via environment variables

If no license key is set in code, MediatR looks for one in environment variables. This is convenient for containerized and cloud environments, and for enterprises that share a single key across many services without code changes:

  • MEDIATR_LICENSE_KEY – the MediatR-specific license key.
  • LUCKYPENNY_LICENSE_KEY – a shared key usable across Lucky Penny products (for example, AutoMapper reads the same variable). Because it is shared, the key must be for a license that includes MediatR (a Bundle or MediatR edition); an AutoMapper-only license will not validate here.

The license key is resolved in the following order of precedence, using the first value found:

  1. An explicit value set in code (cfg.LicenseKey or Mediator.LicenseKey).
  2. The MEDIATR_LICENSE_KEY environment variable.
  3. The LUCKYPENNY_LICENSE_KEY environment variable.

No code change is required when using an environment variable—just register MediatR as usual without setting the license key.

You can register for your license key at MediatR.io

Showing the top 20 packages that depend on MediatR.

Packages Downloads
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 144
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 147
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 149
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 150
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 151
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 153
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 154
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 156
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 158
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 159
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 161
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 162
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 163
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 179
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 328
MediatR.Extensions.Microsoft.DependencyInjection
MediatR extensions for ASP.NET Core
 732

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