Extensions

How to Extend Squidex and the Different Extension Points for Customization.

Introduction

This document describes how to write extensions for Squidex. We assume that you know the basic principles of C# and ASP.NET Core. Otherwise, it might be very hard to write custom extensions.

We use interfaces for all components, which can then be replaced with custom implementations. The default dependency injection system is used to register services. (see https://docs.microsoft.com/en-us/aspnet/core/fundamentals/dependency-injection).

Furthermore, you can extend Squidex with custom HTTP endpoints. Due to the static nature of the Management UI (which is built with Typescript and Angular and has a compilation and bundling process), you cannot extend the UI, except in a few cases where its been made possible.

Read the following article to understand how to write custom editors for the Management UI:

Custom Editors

How to Write a Custom Plugin

So far (as of October 2019), Squidex has a limited plugin architecture that can be used for most cases. In this section we will give you an introduction how to write this type of plugin, and how to register it in Squidex.

In this tutorial we use Squidex.Extensions project as an example, which also contains a sample plugin.

1. Clone the source code

Checkout the source code from GitHub:

[email protected]:Squidex/squidex.git

You only need the source code for development. There are other approaches on how to deploy the newest version of Squidex with your plugin.

2. Create a .NET Core Class Library

First, you need to create a new .NET class library to the backend solution:

Squidex.Extensions Plugin

Ensure that you target netcoreapp3.0.

Then add references to the following other projects in the solution:

  1. Squidex.Domain.Apps.Entities

  2. Squidex.Web

This will implicitly create references to all other projects that might be needed.

The reference projects contain interfaces as well as implementations - which is a problem, because it's hard to figure out which classes should be used in custom plugins. Implementations are subject to change and should not be used directly. Therefore we plan to restructure the content and create implicit contract projects, which don't contain implementation details.

3. Create a New Plugin Class.

A plugin class is used to register all implementations to Squidex. In this example we create a custom plugin which registers an asset store and keeps all files in memory. We register it only when it's activated via the configuration system, so either from the appSettings.json file, command line arguments or environment variables.

namespace Squidex.Extensions.Samples.AssetStore
{
    public sealed class MemoryAssetStorePlugin : IPlugin
    {
        public void ConfigureServices(IServiceCollection services, IConfiguration config)
        {
            var storeType = config.GetValue<string>("assetStore:type");

            if (string.Equals(storeType, "Memory", StringComparison.OrdinalIgnoreCase))
            {
                services.AddSingletonAs<MemoryAssetStore>()
                    .As<IAssetStore>();
            }
        }
    }
}

You can also add multiple implementations to your class library if you have multiple extensions in one project and want to group them together.

3. Reference your plugin

Add a reference to your plugin in the Squidex project.

Add reference to your plugin

Furthermore, you need to add the path to your plugin to the configuration, for example to the appSettings.json file. As we reference the plugin, it will be automatically copied to the output folder when the build or packaging is executed.

Reference your plugin in the configuration file

There is also a project on GitHub that demonstrates how to create a plugin for SendGrid with an older version of Squidex: https://github.com/squidexcontrib/sendgrid

Extension Points

There are a few extension points that can be used for custom functionality.

Rule Actions

Rule actions are used to integrate external systems to Squidex. Therefore, we have written a guide to show you how to write your first rule action here:

Custom Rule Action

Controllers

You can write your own controllers, but you have to extract them from the ApiController class. Your controllers are available under the /api path, because all other requests will be forwarded to the Management UI. The ApiController enforces this rule and ensures the correct routing.

public sealed class PluginController : ApiController
{
    public PluginController(ICommandBus commandBus)
        : base(commandBus)
    {
    }

    [Route("/plugins/sample")]
    public IActionResult Test()
    {
        return Ok(new { text = "I am Plugin" });
    }
}

Infrastructure Extensions

IAssetStore

The Squidex.Infrastructure.Assets.IAssetStore interface is used to encapsulate storage solutions for assets. Currently there are the following implementations:

Recommended implementations:

  • Amazon S3

IEventStore

The Squidex.Infrastructure.CQRS.Events.IEventStore is our abstraction for different event store implementations. You can append to events, query them or subscribe to events. Depending on your implementation, you might want to use the pub-sub system for subscriptions. The notification mechanism is provided by the Squidex.Infrastructure.CQRS.Events.IEventNotifier interface. Currently, there are these implementations as follows:

Recommended implementations:

  • SQL Databases

The Squidex.Infrastructure.CQRS.Events.IEventConsumerInfoRepository defines the contract for a system to store the current state of each event consumer.

IAssetThumbnailGenerator

The Squidex.Infrastructure.Assets.IAssetThumbnailGenerator interface encapsulates image transformations. We only have an implementation for ImageSharp: https://github.com/SixLabors/ImageSharp

Repositories

You can provide other implementations for repositories, e.g. for Elastic Search or SQL:

  • Squidex.Domain.Apps.Entities.Assets.Repositories.IAssetRepository: Stores metadata about assets such as names and sizes, but not the content itself. It can be challenging to implement the filtering.

  • Squidex.Domain.Apps.Entities.Contents.Repositoriess.IContentRepository: Stores the content itself. It can be challenging to implement the filtering.

  • Squidex.Domain.Apps.Read.History.Repositories.IHistoryEventRepository: Stores basic history events to show them in the UI.

  • Squidex.Domain.Apps.Entities.Rules.Repositories.IRuleEventRepository: Stores the rule events, like an internal job queue.

  • Squidex.Infrastructure.States.IStore: Key value store for JSON objects. It contains everything else like comments, apps, schemas, rules, custom indices and settings.

  • Squidex.Infrastructure.UsageTracking.IUsageTracking: Stores historic usage information and performance metrics.

Command Middleware

Command middlewares are used to handle commands, for example when a new content item is created. They run in a pipeline and can be used for a lot of different purposes. It's safe to implement the ICustomCommandMiddleware interface which ensures that your commands are running in the correct order.

namespace Squidex.Infrastructure.CQRS.Commands
{
    public interface ICustomCommandMiddleware
    {
        Task HandleAsync(CommandContext context, Func<Task> next);
    }
}

They accept two parameters. The first is the command context that also includes a reference to the command. The next is a function to call the next command handler. Typical use cases are changes to one domain object, for example default fields for new schemas.

Example 1: Handle Command

If you can accept the command, handle it and call Complete().

class MyHandler : ICustomCommandMiddleware
{
    public async Task HandleAsync(CommandContext context, Func<Task> next) 
    {
        if (context.Command is MyCommand myCommand)
        {
            await Handle(myCommand);
            context.Complete();
        }
        else
        {
            await next();
        }
    }
}

Example 2: Measure Performance

class MyHandler : ICustomCommandMiddleware
{
    public async Task HandleAsync(CommandContext context, Func<Task> next) 
    {
        var watch = Stopwatch.StartNew();

        try
        {
            await next();
        }
        finally
        {
            watch.Stop();

            Log(watch);
        }
    }
}

Example 3: Enrich Command

class MyHandler : ICustomCommandMiddleware
{
    public async Task HandleAsync(CommandContext context, Func<Task> next) 
    {
        if (context.Command is UserCommand userCommand)
        {
            userCommand.UserId = await GetUserIdAsync();
        }

        await next();
    }
}

Event Consumers

Event consumers are invoked when new events are created or when an event consumer is restarted and old events are replayed. You shouldn't raise new events, but of course you can create a new event.

namespace Squidex.Infrastructure.CQRS.Events
{
    public interface IEventConsumer
    {
        // The name of the event consumer to display in the UI.
        string Name { get; }

        // Filter events by the stream name. Use regular expressions.
        string EventsFilter { get; }

        // Implement this method if you are interested to filter events before they are deserialized.
        bool Handles(StoredEvent @event);

        // Will be invoked when the event consumer is restarted.
        Task ClearAsync();

        // Will be called for each new or replayed event.
        Task On(Envelope<IEvent> @event);
    }
}
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