Added details of content type filters.

Author: AndyButland

15/umbraco-cms/SUMMARY.md

@@ -413,6 +413,7 @@
   * [Setup OAuth using Postman](reference/management-api/postman-setup-swagger.md)
 * [Custom Swagger API](reference/custom-swagger-api.md)
 * [Umbraco Flavored Markdown](reference/umbraco-flavored-markdown.md)
+* [Content Type Filters](reference/content-type-filters.md)
 
 ## Tutorials
 

15/umbraco-cms/reference/content-type-filters.md

@@ -0,0 +1,73 @@
+---
+description: Describes how to use content type filters to restrict the allowed content options available to editors.
+---
+
+# Filtering Allowed Content Types
+
+When creating content editors are presented with a dialog where they select the type of content they want to create. The options available are defined when setting up the document, media and member types in the _Settings_ section.
+
+Sometimes implementors or packages have a requirement to use some additional logic to determine which options are available.
+
+This is possible using content type filters.
+
+{% hint style="info" %}
+The uses cases supported here are similar to those where the `SendingAllowedChildrenNotification` would be used in Umbraco 13 or earlier.
+{% endhint %}
+
+## Implementing a Content Type Filter
+
+To create a content type filter you use a class that implements the `IContentTypeFilter` interface (found in the `Umbraco.Cms.Core.Services.Filters` namespace).
+
+There are two methods you can implement. One is for filtering the content types allowed at the content root. The other is for the content types allowed below a given parent node.
+
+If you don't want to filter for one or other method, you can just return the provided collection unmodified.
+
+The following example shows a typical use case. Often websites will have a "Home Page" document type which is created at the root. Normally, only one of these is required. You can enforce that using the following content type filter.
+
+Here we are querying the existing content available at the root. Normally we can create a "Home Page" here, but if one already exists, we remove the option:
+
+```csharp
+internal class OneHomePageOnlyContentTypeFilter : IContentTypeFilter
+{
+    private readonly IContentService _contentService;
+
+    public OneHomePageOnlyContentTypeFilter(IContentService contentService) => _contentService = contentService;
+
+    public Task<IEnumerable<TItem>> FilterAllowedAtRootAsync<TItem>(IEnumerable<TItem> contentTypes)
+        where TItem : IContentTypeComposition
+    {
+        var docTypeAliasesToExclude = new List<string>();
+
+        const string HomePageDocTypeAlias = "homePage";
+        var docTypeAliasesAtRoot = _contentService.GetRootContent()
+            .Select(x => x.ContentType.Alias)
+            .Distinct()
+            .ToList();
+        if (docTypeAliasesAtRoot.Contains(HomePageDocTypeAlias))
+        {
+            docTypeAliasesToExclude.Add(HomePageDocTypeAlias);
+        }
+
+        return Task.FromResult(contentTypes
+            .Where(x => docTypeAliasesToExclude.Contains(x.Alias) is false));
+    }
+
+    public Task<IEnumerable<ContentTypeSort>> FilterAllowedChildrenAsync(IEnumerable<ContentTypeSort> contentTypes, Guid parentKey)
+        => Task.FromResult(contentTypes);
+}
+```
+
+Content type filters are registered as a collection, so it's possible to have more than one either in the solution or an installed package.
+
+You use a composer to register the filters:
+
+```csharp
+public class MyComposer : IComposer
+{
+    public void Compose(IUmbracoBuilder builder)
+    {
+        builder.ContentTypeFilters()
+            .Append<OneHomePageOnlyContentTypeFilter>();
+    }
+}
+```

15/umbraco-cms/reference/notifications/sendingallowedchildrennotifications.md

@@ -4,82 +4,6 @@ description: Example of how to use a SendingAllowedChildren Notification
 
 # Sending Allowed Children Notification
 
-The `SendingAllowedChildrenNotification` enables you to manipulate the Document Types that will be shown in the create menu when adding new content in the backoffice.
+The `SendingAllowedChildrenNotification` is no longer available in Umbraco 15.
 
-## Usage
-
-With the example below we can ensure that a Document Type cannot be selected if the type already exists in the Content tree.
-
-```csharp
-using System.Web;
-using Umbraco.Cms.Core.Events;
-using Umbraco.Cms.Core.Notifications;
-
-namespace Umbraco.Docs.Samples.Web.Notifications;
-
-public class SendingAllowedChildrenNotificationHandler : INotificationHandler<SendingAllowedChildrenNotification>
-{
-    public void Handle(SendingAllowedChildrenNotification notification)
-    {
-        const string contentIdKey = "contentId";
-
-            // Try get the id from the content item in the backoffice
-            var queryStringCollection = HttpUtility.ParseQueryString(notification.UmbracoContext.OriginalRequestUrl.Query);
-
-        if (!queryStringCollection.ContainsKey(contentIdKey))
-        {
-            return;
-        }
-
-        var contentId = queryStringCollection[contentIdKey].TryConvertTo<int>().ResultOr(-1);
-
-        if (contentId == -1)
-        {
-            return;
-        }
-
-        var content = notification.UmbracoContext.Content?.GetById(true, contentId);
-
-        if (content is null)
-        {
-            return;
-        }
-
-        // Allowed children as configured in the backoffice
-        var allowedChildren = notification.Children.ToList();
-
-        if (content.ChildrenForAllCultures is not null)
-        {
-            // Get all children of current page
-            var childNodes = content.ChildrenForAllCultures.ToList();
-
-            // If there is a Settings page already created, then don't allow it anymore
-            // You can also use the ModelTypeAlias property from your PublishedModel for comparison,
-            // like Settings.ModelTypeAlias if you have set models builder to generate SourceCode models
-            if (childNodes.Any(x => x.ContentType.Alias == "settings"))
-            {
-                allowedChildren.RemoveAll(x => x.Alias == "settings");
-            }
-        }
-
-        // Update the allowed children
-        notification.Children = allowedChildren;
-    }
-}
-```
-
-You also need to register this notification handler. You can achieve this by updating the `Program` class like:
-
-```csharp
-builder.CreateUmbracoBuilder()
-    .AddBackOffice()
-    .AddWebsite()
-    .AddDeliveryApi()
-    .AddComposers()
-    .AddNotificationHandler<SendingAllowedChildrenNotification, SendingAllowedChildrenNotificationHandler>()
-    .Build();
-```
-
-{% hint style="info" %}
-For more information about registering notifications read the [Registering notification handlers](./) article.
-{% endhint %}
+Please see [content type filters](../content-type-filters.md) as the supported alternative for use cases that previously relied on this notification.