Composing

This article covers the topic of composing in Umbraco.

Customising the behaviour of an Umbraco Application at 'start up'. for example adding, removing, or replacing the core functionality of Umbraco or registering custom code to subscribe to notifications.

Overview

An Umbraco application is a Composition made of many different 'collections' and single items of specific functionality/implementation logic/components (eg. UrlProviders, ContentFinders - see below for a full list). These collections are populated when the Umbraco Application starts up.

'Composing' is the term used to describe the process of curating which pieces of functionality should be included in a particular collection. The code that implements these choices at start up is called a Composer.

A Component is a generic wrapper for writing custom code during composition, it has two methods: Initialize() and Terminate() and these are executed when the Umbraco Application starts up, and when it shuts down, respectively. The functionality of a Component is identical to having a class handling both the UmbracoApplicationStartingNotification and UmbracoApplicationStoppingNotification.

How are the collections populated? - Either by scanning the codebase for c# classes that inherit from a particular base class or implement a particular interface (typed scanned) or by being explicitly registered via a Composer.

Umbraco setup the default set of components and collections that deliver the core 'out of the box' Umbraco behaviour. These default collections can be removed, reordered, replaced, etc. by implementing IComposer's and IComponents to customise and extend Umbraco's behaviour.

Example - Creating a Composer to listen for ContentSavingNotification

This example shows how to create a component and a notification handler for the ContentSavingNotification, (perhaps to check for explicit words, or some custom business logic that needs to run before the content item is saved in Umbraco).

We create a new C# class that implements IComposer and use it register our notification handler.

using System.Linq;
using Umbraco.Cms.Core.Composing;
using Umbraco.Cms.Core.DependencyInjection;
using Umbraco.Cms.Core.Events;
using Umbraco.Cms.Core.Notifications;
using Umbraco.Extensions;

namespace My.Website;

public class SubscribeToContentServiceSavingComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        builder.AddNotificationHandler<ContentSavingNotification, CustomContentSavingNotificationHandler>();
    }
}

public class CustomContentSavingNotificationHandler : INotificationHandler<ContentSavingNotification>
{
    public void Handle(ContentSavingNotification notification)
    {
        foreach (var content in notification.SavedEntities
            // Check if the content item type has a specific alias
            .Where(c => c.ContentType.Alias.InvariantEquals("MyContentType")))
        {
            // Do something if the content is using the MyContentType doctype
        }
    }
}

Ordering of composers is important, the last one added can override a previously added composer! Make sure, when overriding, that your composer that is doing the overriding, is 'composing', after the composer has 'composed' the element you wish to override!

Example - Explicitly Registering a new custom OEmbedProvider

This example shows a custom 'Spotify' OEmbed Provider which will allow Spotify URLs to be used via the 'embed' button in the Rich Text Editors. As the collection for OEmbedProviders is not 'typed scanned', we need to explicitly register the provider in the collection of OEmbedProviders. We create a C# class which implements IComposer and append our new Spotify OEmbedProvider to the EmbedProvidersCollection:

using Umbraco.Cms.Core.Media.EmbedProviders;
using Umbraco.Cms.Core.Serialization;

namespace My.Website;

public class SpotifyEmbedProvider : OEmbedProviderBase
{
    public SpotifyEmbedProvider(IJsonSerializer jsonSerializer)
        : base(jsonSerializer)
    {
    }

    public override string ApiEndpoint => "https://embed.spotify.com/oembed/";

    // Playlist
    // https://open.spotify.com/user/spotify/playlist/37i9dQZF1E4sNI4jZloSZr?si=cueBooBfTnqCGriSa4N_Kg
    // spotify:user:spotify:playlist:37i9dQZF1E4sNI4jZloSZr
    // Artist
    // https://open.spotify.com/artist/0iirUbtgwt9jEkc2Grin8C?si=TLeUR2cHR-KPRJJhW6YiVg
    // spotify:artist:0iirUbtgwt9jEkc2Grin8C
    // Album
    // https://open.spotify.com/album/0lvtdqkqIln6uDBBUT7DHL?si=XTVJIEmnS_OVv9l6ktPFiw
    // spotify:album:0lvtdqkqIln6uDBBUT7DHL
    // Track
    // https://open.spotify.com/track/7aCk4XfXIEJM2MecU6Gmf2?si=vESDzI0xTNeA9FQ_dvf1eQ
    // spotify:track:7aCk4XfXIEJM2MecU6Gmf2
    public override string[] UrlSchemeRegex => new[]
    {
        @".*.spotify.com/.*",
        @"spotify:.*"
    };

    public override Dictionary<string, string> RequestParams => new();

    public override string? GetMarkup(string url, int maxWidth = 0, int maxHeight = 0)
    {
        string requestUrl = base.GetEmbedProviderUrl(url, maxWidth, maxHeight);
        OEmbedResponse? oembed = base.GetJsonResponse<OEmbedResponse>(requestUrl);

        return oembed?.GetHtml();
    }
}

using Umbraco.Cms.Core.Composing;

namespace My.Website;

public class RegisterEmbedProvidersComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        // Change the EmbedProvidersCollection
        // by adding our new EmbedProvider for Spotify
        builder.EmbedProviders().Append<SpotifyEmbedProvider>();
    }
}

See a list of collections below to determine which are 'type scanned' and which require explicit registration.

ComponentComposer

It's an implementation of IComposer, that provides a quicker way to add a custom component to the Component's collection. Creating a C# class that inherits from ComponentComposer<YourComponentType> will automatically add YourComponentType to the collection of Components. In the example above, the SubscribeToContentServiceSavingComposer for the SubscribeToContentServiceSavingComponent could have been written more conveniently as:

public class SubscribeToContentServiceSavingComposer : ComponentComposer<SubscribeToContentServiceSavingComponent>
{ }

Collections

"Collections of elements", for example, the ContentFinders collection. - Collections are another concept that Umbraco uses to make things simpler, on top of DI. A collection builder builds a collection, allowing users to add and remove types before anything is registered into DI.

Below is a list of collections with their corresponding 'collection type' and how items for this collection 'out of the box' are registered.

Collection	Type	Registration
Actions	Lazy	Type scanned for IAction
BackOfficeAssets	Ordered	Explicit Registration - Empty by default
CacheRefreshers	Lazy	Type scanned for ICacheRefresher
Components	Ordered	Explicit Registration
ContentApps	Ordered	Package.manifest & Explicit Registration
ContentFinders	Ordered	Explicit Registration
ContentIndexHandlers	Lazy	Type scanned for IContentIndexHandler
Dashboards	Weighted	Package.manifest & Explicit Registration
DataEditors	Lazy	Type scanned for IDataEditor
DataValueReferenceFactories	Ordered	Explicit Registration - Empty by default
EditorValidators	Lazy	Type scanned for IEditorValidator
EmbedProviders	Ordered	Explicit Registration
FilterHandlers	Lazy	Type scanned for IFilterHandler
HealthChecks	Lazy	Type scanned for HealthCheck
HealthCheckNotificationMethods	Lazy	Type scanned for IHealthCheckNotificationMethod
ManifestFilters	Ordered	Explicit Registration - Empty by default
ManifestValueValidators	Set	Explicit Registration
MapDefinitions	Set	Explicit Registration
Mappers	Set	Explicit Registration
MediaUrlGenerators	Set	Explicit Registration
MediaUrlProviders	Ordered	Explicit Registration
NPocoMappers	Set	Explicit Registration
PackageMigrationPlans	Lazy	Type scanned for PackageMigrationPlan
PartialViewSnippets	Lazy	Explicit Registration. Reads .cshtml files from Umbraco.Cms.Core.EmbeddedResources.Snippets assembly
PropertyValueConverters	Ordered	Type scanned for IPropertyValueConverter
RuntimeModeValidators	Set	Explicit Registration
SearchableTrees	Lazy	Type scanned for ISearchableTree
Sections	Ordered	Package.manifest & Explicit Registration
SelectorHandlers	Lazy	Type scanned for ISelectorHandler
SortHandlers	Lazy	Type scanned for ISortHandler
TourFilters	Base	Empty collection
Trees	Base	Type scanned. Must inherit TreeControllerBase & use [Tree]
UrlProviders	Ordered	Explicit Registration
UrlSegmentProviders	Ordered	Explicit Registration
Validators	Lazy	Explicit Registration

Types of Collections

	Method	Notes
Set	SetCollectionBuilderBase	The base class for collection builders that do not order their items explicitly.
Ordered	OrderedCollectionBuilderBase	The base class for collection builders that order their items explicitly.
Weighted	WeightedCollectionBuilder	The base class for collection builders that order their items by the [Weight] attribute.
Lazy	LazyCollectionBuilderBase	The base class for collection builders that resolve the types at the last moment, only when the collection is required.

Example - Modifying Collections

This example shows how to control which Healthchecks are available to run in the Umbraco backoffice. Create a C# class which implements IComposer, the Compose method gives access to the HealthChecks collection of the Umbraco Composition - first we clear all HealthChecks from the collection, then add back in the ones we want to keep:

using Umbraco.Cms.Core.Composing;
using Umbraco.Cms.Core.DependencyInjection;
using Umbraco.Cms.Core.HealthChecks.Checks.Permissions;
using Umbraco.Cms.Core.HealthChecks.Checks.Security;

namespace My.Website;

public class MyComposer: IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        // Remove all HealthChecks
        builder.HealthChecks().Clear();

        // Explicitly add back the ones we want to use
        builder.HealthChecks().Add<FolderAndFilePermissionsCheck>();
        builder.HealthChecks().Add<ExcessiveHeadersCheck>();
    }
}

Attributes

Umbraco has some useful C# attributes to decorate your composer classes or Types used in collections, to give you further control on how and when your Composers will 'compose'.

ComposeBefore and ComposeAfter

A finer-grain mechanism can then be used to refine the order of composition. Each composer can specify that it should compose before or after another composer, using the ComposeBefore and ComposeAfter attributes. For instance:

[ComposeBefore(typeof(ThatOtherComposer))]
public class ThisComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
    }
}

ThisComposer will 'compose' before ThatOtherComposer.

If you create a circular dependency then Umbraco will fail to boot and will report the conflicting/circular dependency.

Weight

This attribute is used only for WeightedCollectionBuilders (see list above). It specifies an integer ordinal value for each item to be added to the weighted collection which controls their sort order. The weighting attribute is not applied to the Composers.

using System;
using Umbraco.Core;
using Umbraco.Core.Composing;
using Umbraco.Core.Dashboards;

namespace Umbraco.Web.Dashboards;

[Weight(10)]
public class FormsDashboard : IDashboard
{
    public string Alias => "formsInstall";
    public string[] Sections => new [] { Constants.Applications.Forms };
    public string View => "views/dashboard/forms/formsdashboardintro.html";
    public IAccessRule[] AccessRules => Array.Empty<IAccessRule>();
}

HideFromTypeFinder

This is used to hide a type from being auto-scanned/added to a collection as in some cases certain items/types may need to be added to a collection manually. For example, a Search package may make it optional whether to replace the 'backoffice search' with an ISearchableTree implementation. Type scanning would make this change automatically at start up if the custom implementation was detected via type scanning. This attribute could hide the class from the scanner.

DisableComposer & Disable

These attributes allow you to disable a particular implementation of a composer or class - Let's say Umbraco ships with two different ways of doing "something" (for instance, two front-end caches). Each way has its own composer, which registers all the relevant elements. Keep in mind that if both composers are detected, there will be some sort of collision. Ideally, we want to disable one of them. That can be achieved with the Disable attribute:

[Disable]
public class Way2Composer : IComposer
{
    //...
}

When used without arguments, these attributes apply to the composer they are marking. But, and this is where it becomes interesting, they can be used with an argument to act on another component. Therefore, should a user want to replace our "something" with theirs, they would write the following code:

[Disable(typeof(Way1Composer))]
public class MyComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        // ...
    }
}

But maybe they want to swap our two "something" implementations? In this case, assembly-level attributes can be used:

[assembly:DisableComposer(typeof(Way1Composer))]
[assembly:EnableComposer(typeof(Way2Composer))]

Umbraco also has [Enable] & [EnableComposer] attributes but all composers are enabled by default.

Runtime Levels

The Umbraco.Cms.Core.RuntimeLevel enum contains the following values:

BootFailed

The runtime has failed to boot and cannot run.

Unknown

The level is unknown.

Boot

The runtime is booting.

Install

The runtime has detected that Umbraco is not installed at all, ie. there is no database, and is currently installing Umbraco.

Upgrade

The runtime has detected an Umbraco install which needed to be upgraded, and is currently upgrading Umbraco.

Run

The runtime has detected an up-to-date Umbraco install and is running.

Level	Description
BootFailed	The runtime has failed to boot and cannot run.
Unknown	The level is unknown.
Boot	The runtime is booting.
Install	The runtime has detected that Umbraco is not installed at all, ie. there is no database, and is currently installing Umbraco.
Upgrade	The runtime has detected an Umbraco install that needed to be upgraded and is currently upgrading Umbraco.
Run	The runtime has detected an up-to-date Umbraco install and is running.

Example of using Ordered Collections and adding types explicitly

You may wish to create an Umbraco package that allows package consumers to extend and add additional functionality. In this example, we show how you can use the OrderedCollectionBuilderBase.

using Microsoft.AspNetCore.Mvc;
using Umbraco.Cms.Api.Management.Controllers;
using Umbraco.Cms.Api.Management.Routing;
using Umbraco.Cms.Core.Composing;

namespace UmbracoDocs.Samples;

public interface IDoThing
{
    string DoTheThing(string message);
}

public class FirstThing : IDoThing
{
    public string DoTheThing(string message)
        => $"First: {message}";
}

public class SecondThing : IDoThing
{
    public string DoTheThing(string message)
        => $"Second: {message}";
}

public class ThirdThing : IDoThing
{
    public string DoTheThing(string message)
        => $"Third: {message}";
}

// OrderedCollection - use when order of items is important (You may want to execute them in order)
public class DoThingsCollectionBuilder : OrderedCollectionBuilderBase<DoThingsCollectionBuilder, DoThingsCollection, IDoThing>
{
    protected override DoThingsCollectionBuilder This => this;
}

public class DoThingsCollection : BuilderCollectionBase<IDoThing>
{
    public DoThingsCollection(Func<IEnumerable<IDoThing>> items)
        : base(items)
    {
    }
}

public class DoThingsComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        // Explicitly add to the collection a Type in a specific order
        builder
            .WithCollectionBuilder<DoThingsCollectionBuilder>()
            .Append<FirstThing>()
            .Append<SecondThing>()
            .Append<ThirdThing>();
    }
}

// An Umbraco Management API Controller - used in a Dashboard or Property Editor, perhaps?
[ApiExplorerSettings(GroupName = "Do things")]
[VersionedApiBackOfficeRoute("do/things")]
public class DoThingsController : ManagementApiControllerBase
{
    private readonly DoThingsCollection _doThings;

    public DoThingsController(DoThingsCollection doThings)
        => _doThings = doThings;

    [HttpGet]
    [ProducesResponseType<string[]>(StatusCodes.Status200OK)]
    public IActionResult DoAllThings(string message)
    {
        var allThingsDone = _doThings
            .Select(doThing => doThing.DoTheThing(message))
            .ToArray();

        return Ok(allThingsDone);
    }
}

Example of using Lazy Collections with Type Scanning

You may wish to create an Umbraco package that allows package consumers to extend and add additional functionality. In this example, we show how you can use the LazyCollectionBuilderBase to scan assemblies that implement your interface by using the TypeLoader

Don't use type scanning if you can avoid it. Type scanning increases the Umbraco boot time.

If your use case requires type scanning, ensure your interface implements IDiscoverable. This marker interface ensures that types are scanned once and then cached by Umbraco. This way, we save time by not having to re-scan for types repeatedly.

using Microsoft.AspNetCore.Mvc;
using Umbraco.Cms.Api.Management.Controllers;
using Umbraco.Cms.Api.Management.Routing;
using Umbraco.Cms.Core.Composing;

namespace UmbracoDocs.Samples;

// Implement `IDiscoverable` to boost scanning performance
public interface IDoThing : IDiscoverable
{
    string DoTheThing(string message);
}

public class FirstThing : IDoThing
{
    public string DoTheThing(string message)
        => $"First: {message}";
}

public class SecondThing : IDoThing
{
    public string DoTheThing(string message)
        => $"Second: {message}";
}

public class ThirdThing : IDoThing
{
    public string DoTheThing(string message)
        => $"Third: {message}";
}

public class DoThingsCollectionBuilder : LazyCollectionBuilderBase<DoThingsCollectionBuilder, DoThingsCollection, IDoThing>
{
    protected override DoThingsCollectionBuilder This => this;
}

public class DoThingsCollection : BuilderCollectionBase<IDoThing>
{
    public DoThingsCollection(Func<IEnumerable<IDoThing>> items)
        : base(items)
    {
    }
}

public class DoThingsComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        // Add types from assemblies. Be conscious of using type scanning, as this adds to the Umbraco boot time.
        // If you need to use type scanning, ensure that your interface implements `IDiscoverable`.
        builder
            .WithCollectionBuilder<DoThingsCollectionBuilder>()
            .Add(() => builder.TypeLoader.GetTypes<IDoThing>());
    }
}

// An Umbraco Management API Controller - used in a Dashboard or Property Editor, perhaps?
[ApiExplorerSettings(GroupName = "Do things")]
[VersionedApiBackOfficeRoute("do/things")]
public class DoThingsController : ManagementApiControllerBase
{
    private readonly DoThingsCollection _doThings;

    public DoThingsController(DoThingsCollection doThings)
        => _doThings = doThings;

    [HttpGet]
    [ProducesResponseType<string[]>(StatusCodes.Status200OK)]
    public IActionResult DoAllThings(string message)
    {
        var allThingsDone = _doThings
            .Select(doThing => doThing.DoTheThing(message))
            .ToArray();

        return Ok(allThingsDone);
    }
}