Composing

    Customising the behaviour of an Umbraco Application at 'start up'. eg 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' 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 explictly 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 - Explicity 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 for words, or some custom business logic that needs to run before the content item is saved in Umbraco).

    We create a new c# class which 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
    {
        [RuntimeLevel(MinLevel = RuntimeLevel.Run)]
        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()
            {
            }
    
            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. They implement the following Composer interfaces which group together the composers and control the order in which they are run:
    IRuntimeComposer
    There should only ever been one IRuntimeComposer in an application and it belongs to Umbraco, this Composer runs first before all other composers, do not mess with the IRuntimeComposer.

    ICoreComposer
    After the IRuntimeComposer has 'composed' - all ICoreComposer instances also 'compose'. They compose all the default elements that Umbraco needs to run.

    IUserComposer
    Finally, all IUserComposer instances 'compose'. These types of composers are for developers/implementors to use to customise and extend Umbraco or 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>

    Is an implementation of IUserComposer, that provides a quicker way to add a custom Component to the Component's collection. Creating a c# class that inhertits 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:

            [RuntimeLevel(MinLevel = RuntimeLevel.Run)]
            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 actually 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
    {
        [RuntimeLevel(MinLevel = RuntimeLevel.Run)]
        public class MyComposer : IUserComposer
        {
            public void Compose(Composition composition)
            {
                //Remove all HealthChecks
                composition.HealthChecks().Clear();
    
                //Explictly 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 dependancy then Umbraco will fail to boot and will report the conflicting/circular dependancy.

    [Weight]

    This attribute is used only for WeightedCollectionBuilders (see list above) - and specifies an integer ordinal value for each item to be added to the weighted collection which controls their sort order - (note 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 allows 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. Of course, 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 void 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 hers, she would write the following code:

    [Disable(typeof(Way1Composer))]
    public void MyComposer : IComposer
    {
        public void Compose(Composition composition)
        { ... }
    }
    

    But maybe she just wants 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 usecase 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.

    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.