Restrict content types in properties

Restrict a ContentArea

The AllowedTypes attribute (placed in the EPiServer.DataAnnotations namespace, EPiServer assembly) can be applied to a property.

As you can see from examples below, the array declaration is not needed.

[AllowedTypes(new [] {
  typeof (PageData)
})]
public virtual ContentArea RelatedContentArea {
  get;
  set;
}

[AllowedTypes(typeof (PageData))]
public virtual ContentArea OtherRelatedContentArea {
  get;
  set;
}

The same attribute can also be set as:

[AllowedTypes(AllowedTypes = new [] {
  typeof (PageData)
})]
public virtual ContentArea RelatedContentArea {
  get;
  set;
}

When an item that is part of the allowed types is dragged over this property, the property is highlighted, and the editor can add the item to the property. But if the editor tries to drag another item that is not part of the allowed types, the property is grayed out, and the item cannot be added. The content selector dialog is also filtered out accordingly. Through the Create a new block link in the content area, editors can only add allowed item types.

You can specify several allowed types and inherited types:

[AllowedTypes(new [] {
  typeof (PageData), typeof (BlockData)
})]
public virtual ContentArea RelatedContentArea {
  get;
  set;
}

[AllowedTypes(typeof (PageData), typeof (BlockData))]
public virtual ContentArea OtherRelatedContentArea {
  get;
  set;
}

Restrict a certain set of types but allow others

The AllowedTypes attribute can also be used to restrict certain types from a larger pool of types. 
For example, if you supply two arrays of types as constructor arguments, the first array argument considers allowed items, while the second argument considers restricted items.

[AllowedTypes(new [] {
  typeof (BlockData)
}, new [] {
  typeof (EditorialBlock)
})]
public virtual ContentArea RelatedContentArea {
  get;
  set;
}

or

[AllowedTypes(AllowedTypes = new [] {
  typeof (BlockData)
}, RestrictedTypes = new [] {
  typeof (EditorialBlock)
})]
public virtual ContentArea RelatedContentArea {
  get;
  set;
}

In this case, you can add BlockData items to the content area except the EditorialBlock, which is a BlockData but also part of restricted types. When an editor drags the EditorialBlock or its subtypes, the content area is grayed out. Similarly, when an editor clicks the Create a new block link, the content selector is filtered out accordingly.

Restrict based on base classes and interfaces

When you place the AllowTypes attribute on a ContentArea, ContentReference or a list of ContentReference property, the user interface not only allows and restricts based on the given type but also on the given type's subtypes. For example:

[AllowedTypes(new [] {
  typeof (SiteBlockData)
})]
public virtual ContentArea RelatedContentArea {
  get;
  set;
}

In this case, the property not only adds the SiteBlockData but other types inherited from the SiteBlockData also behave the same.

However, if you want to allow and restrict based on an interface, you must implement the UIDescriptor for the interface.

interface ISpecialInterface { } 
public class SpecialBlock : BlockData, ISpecialInterface {}

If you now want to enable a content area to add blocks (except the ones inherited from the ISpecialInterface), you first have to implement a UIDescriptor for the ISpecialInterface.

[UIDescriptorRegistration]
public class SpecialInterfaceDescriptor : UIDescriptor<ISpecialInterface> { }

Additionally, the interface has to inherit from the IContentData interface.

public interface ISpecialInterface: IContentData {
  // properties and methods
}

After that, place the AllowedTypes on the content area property.

[AllowedTypes(AllowedTypes = new [] {
    typeof (BlockData)
  },
  RestrictedTypes = new [] {
    typeof (ISpecialInterface)
  })]
public virtual ContentArea SomeArea {
  get;
  set;
}

This code adds blocks to SomeArea but restricts blocks that implement ISpecialInterface.

Restrict content reference properties

The AllowedTypes attribute can be used for ContentReference or list of ContentReference properties as well:

[AllowedTypes(typeof (ProductPage))]
public virtual ContentReference SomeLink {
  get;
  set;
}

[AllowedTypes(typeof (ProductPage))]
public virtual IList<ContentReference> SomeLinks {
  get;
  set;
}

This code results in the same behavior for content areas when dragging items to the property; only items of the type ProductPage can be added to the property. Items not allowed (according to the AllowedTypes attribute) are not selectable in the content selector dialog.

Known limitations

• AllowedTypes only works with ContentArea, ContentReference and list of ContentReference properties.
• RestrictedTypes always win. That means that if an item (a class or an interface) is given in RestrictedTypes, its instances and sub-items are restricted whether or not the item or sub-items exist in AllowedTypes.