Composing
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 events.
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. Typically a Component may be used to wire up custom code to handle a particular event in Umbraco. (see content saving example below)
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 ships with a set of ICoreComposer's that pull together the default set of components and collections that deliver the core 'out of the box' Umbraco behaviour. These default collections and components can be removed, reordered, replaced, etc. by implementing IUserComposer's and IComponents to customise and extend Umbraco's behaviour.
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 Grid and 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 IUserComposer and append our new Spotify OEmbedProvider to the OEmbedProviders() collection:
using System.Collections.Generic;
using Umbraco.Web.Media.EmbedProviders;
namespace My.Website
{
public class Spotify : EmbedProviderBase
{
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 string[]
{
@".*.spotify.com/.*",
@"spotify:.*"
};
public override Dictionary<string, string> RequestParams => new Dictionary<string, string>();
public override string GetMarkup(string url, int maxWidth = 0, int maxHeight = 0)
{
var requestUrl = base.GetEmbedProviderUrl(url, maxWidth, maxHeight);
var oembed = base.GetJsonResponse<OEmbedResponse>(requestUrl);
return oembed.GetHtml();
}
}
}
using Umbraco.Core.Composing;
using Umbraco.Web;
namespace My.Website
{
public class CustomOEmbedComposer : IUserComposer
{
public void Compose(Composition composition)
{
// Change the OEmbedProviders collection
// by adding our new EmbedProvider for Spotify
composition.OEmbedProviders().Append<Spotify>();
}
}
}
See a list of collections below to determine which are 'type scanned' and which require explicit registration.
Example - Creating a Component to listen for ContentService.Saving events
This example shows how to create a component to listen and respond to ContentService.Saving events, (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 IUserComposer and use it to add our new IComponent to the collection of Components. When Umbraco starts up, the Initialize() method of the component will be called and the ContentService Saving event will be subscribed to.
using System.Linq;
using Umbraco.Core;
using Umbraco.Core.Composing;
using Umbraco.Core.Events;
using Umbraco.Core.Services;
using Umbraco.Core.Services.Implement;
namespace My.Website
{
public class SubscribeToContentServiceSavingComposer : IUserComposer
{
public void Compose(Composition composition)
{
// Append our component to the collection of Components
// It will be the last one to be run
composition.Components().Append<SubscribeToContentServiceSavingComponent>();
}
}
public class SubscribeToContentServiceSavingComponent : IComponent
{
// initialize: runs once when Umbraco starts
public void Initialize()
{
ContentService.Saving += ContentService_Saving;
}
// terminate: runs once when Umbraco stops
public void Terminate()
{
//unsubscribe during shutdown
ContentService.Saving -= ContentService_Saving;
}
private void ContentService_Saving(IContentService sender, ContentSavingEventArgs e)
{
foreach (var content in e.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
}
}
}
}
Types of Composers
Composers are responsible for drawing together the different components an Umbraco application is composed of.
InitialComposer
The CoreInitialComposer and the WebInitialComposer setup everything required for Umbraco to run. The CoreInitialComposer runs first, followed by the WebInitialComposer . Registering the database builder, services, routes for RenderMvcControllers, APIControllers and SurfaceControllers are some of the resposibilities of these two composers.
These composers run before any other composers and there should only be one instance of each of these composers. They belong to Umbraco and must not be used for any customisations.
After the InitialComposer's there are two groups of composers that execute, they implement the following interfaces to control the order in which they are run:
ICoreComposer
After the WebInitialComposer has 'composed' - all ICoreComposer instances also 'compose'. They compose all the default elements that Umbraco needs to run. Some of the responsibilities covered by ICoreComposers include registering ModelsBuilder, registering the log viewer, registering the component responsible for writing into the audit logs, etc.
IUserComposer
Finally, all IUserComposer instances 'compose'. These types of composers are for developers/implementors to use to customise and extend Umbraco or for use in package development.
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!
ComponentComposer<T>
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>, IUserComposer
{ }
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 |
|---|---|---|
| CacheRefreshers | Lazy | Type scanned for ICacheRefresher |
| Components | Ordered | Explicit Registration |
| ContentApps | Ordered | Package.manifest & Explicit Registration |
| ContentFinders | Ordered | Explicit Registration |
| Dashboards | Weighted | Package.manifest & Type scanned for IDashboard |
| DataEditors | Lazy | Type scanned for IDataEditor |
| FilteredControllerFactory | Ordered | Explicit Registration |
| HealthChecks | Lazy | Type scanned for HealthCheck |
| OEmbedProviders | Ordered | Explicit Registration |
| PackageActions | Lazy | Type scanned for IPackageAction |
| PropertyValueConvertors | Ordered | Type scanned for IPropertyValueConverter |
| SearchableTrees | Lazy | Type scanned for ISearchableTree |
| Sections | Ordered | Package.manifest & Explicit Registration |
| 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
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 IUserComposer, 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.Core;
using Umbraco.Core.Composing;
using Umbraco.Web;
using Umbraco.Web.HealthCheck.Checks.Permissions;
using Umbraco.Web.HealthCheck.Checks.Security;
namespace My.Website
{
public class MyComposer : IUserComposer
{
public void Compose(Composition composition)
{
// Remove all HealthChecks
composition.HealthChecks().Clear();
// Explicitly add back the ones we want to use
composition.HealthChecks().Add<FolderAndFilePermissionsCheck>();
composition.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 : IUserComposer
{
public void Compose(Composition composition)
{
}
}
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(Composition composition)
{
// ...
}
}
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))]
Note that Umbraco also has a [Enable] & [EnableComposer] attributes but all composers are enabled by default.
[RuntimeLevel]
The most common use case for this is to set this attribute on your own composers and to set the minimum level to Run. Which will mean this composer will not be invoked until Umbraco is fully booted and is running. So if an upgrade or Umbraco is still booting, your own custom composer code won't run until everything is all setup and good.
By default, any IUserComposer uses the Minimum Runtime Level of Run & thus does not need to explicitly add the attribute as shown in the example below.
using Umbraco.Core;
using Umbraco.Core.Composing;
namespace My.Website
{
[RuntimeLevel(MinLevel = RuntimeLevel.Run)]
public class MyComposer : IUserComposer
{
public void Compose(Composition composition)
{
}
}
}
If you wish to see the order of components when Umbraco boots, then you can see this information in the logs of Umbraco.
Runtime Levels
The Umbraco.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.
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 System.Collections.Generic;
using Umbraco.Core.Composing;
using Umbraco.Web.WebApi;
namespace TestCollections.Code
{
public interface IMyThing
{
string Name { get; }
string DoSomething(string message);
}
public class ExampleThing : IMyThing
{
public string Name => "Example";
public string DoSomething(string message)
{
return $"Hello {message}";
}
}
// OrderedCollection - use when order of items is important (You may want to execute them in order)
// Different types of collections - https://our.umbraco.com/Documentation/Implementation/Composing/#types-of-collections
public class MyThingsCollectionBuilder : OrderedCollectionBuilderBase<MyThingsCollectionBuilder, MyThingsCollection, IMyThing>
{
protected override MyThingsCollectionBuilder This => this;
}
public class MyThingsCollection : BuilderCollectionBase<IMyThing>
{
public MyThingsCollection(IEnumerable<IMyThing> items)
: base(items)
{ }
}
public static class WebCompositionExtensions
{
public static MyThingsCollectionBuilder MyThings(this Composition composition)
=> composition.WithCollectionBuilder<MyThingsCollectionBuilder>();
}
public class MyThingComposer : IUserComposer
{
public void Compose(Composition composition)
{
// Explicitly add to the collection a Type in a specific order
composition.MyThings().Append<ExampleThing>()
.Append<AnotherThing>()
.Append<SomeOtherThing>();
}
}
// An Umbraco Backoffice Web API Controller - Used in a dashboard or Property Editor perhaps?
public class SomeBackofficeApiController : UmbracoAuthorizedApiController
{
private MyThingsCollection _mythings;
public SomeBackofficeApiController()
{
}
public SomeBackofficeApiController(MyThingsCollection mythings)
{
_mythings = mythings;
}
public List<string> GetMessages(string message)
{
var items = new List<string>();
foreach (var thing in _mythings)
{
items.Add(thing.DoSomething(message));
}
return items;
}
}
}
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
Add types from assemblies - be conscious of doing type scanning, as this adds time to boot up of Umbraco.
If you still need to use type scanning, ensure your Interface implements IDiscoverable as this is a type that is scanned once by Umbraco and the results are cached and then filtered. This saves time by re-scanning for types over and over again.
using System.Collections.Generic;
using Umbraco.Core.Composing;
using Umbraco.Web.WebApi;
namespace TestCollections.Code
{
// Implement `IDiscoverable` (To help with typescanning speed/perf)
public interface IMyThing : IDiscoverable
{
string Name { get; }
string DoSomething(string message);
}
public class ExampleThing : IMyThing
{
public string Name => "Example";
public string DoSomething(string message)
{
return $"Hello {message}";
}
}
public class MyThingsCollectionBuilder : LazyCollectionBuilderBase<MyThingsCollectionBuilder, MyThingsCollection, IMyThing>
{
protected override MyThingsCollectionBuilder This => this;
}
public class MyThingsCollection : BuilderCollectionBase<IMyThing>
{
public MyThingsCollection(IEnumerable<IMyThing> items)
: base(items)
{ }
}
public static class WebCompositionExtensions
{
public static MyThingsCollectionBuilder MyThings(this Composition composition)
=> composition.WithCollectionBuilder<MyThingsCollectionBuilder>();
}
public class MyThingComposer : IUserComposer
{
public void Compose(Composition composition)
{
// Add types from assemblies - be conscious of doing type scanning
// as this adds time to boot up of Umbraco
// If you still need to use type scanning, ensure your Interface implements `IDiscoverable`
composition.MyThings().Add(() => composition.TypeLoader.GetTypes<IMyThing>());
}
}
// An Umbraco Backoffice Web API Controller - Used in a dashboard or Property Editor perhaps?
public class SomeBackofficeApiController : UmbracoAuthorizedApiController
{
private MyThingsCollection _mythings;
public SomeBackofficeApiController()
{
}
public SomeBackofficeApiController(MyThingsCollection mythings)
{
_mythings = mythings;
}
public List<string> GetMessages(string message)
{
var items = new List<string>();
foreach (var thing in _mythings)
{
items.Add(thing.DoSomething(message));
}
return items;
}
}
}