Content metadata properties

This topic provides an introduction to metadata interfaces and metadata properties that can be defined on content models.

In this topic

• How it works
• Usage
  • Shared blocks
• IContentData
• IContent
• IVersionable
• ILocale
• ILocalizable
• IReadOnly/IReadOnly<T>
• IModifiedTrackable
• IChangeTrackable
• IContentSecurable
• IRoutable
• ICategorizable
• IInitializableContent
• Exportable

How it works

EPiServer.Core.IContentData is the base interface that all content models implement. All content types, except BlockData, also implement the EPiServer.Core.IContent interface, which is required for a content instance to have a unique ID and its own lifecycle (that is, can be loaded/saved individually). Through the EPiServer.IContentRepository, you can perform CRUD (Create, Read, Update, Delete) operations on content instances implementing EPiServer.Core.IContent, for example, listing and move.

There are also many additional metadata interfaces a content type can implement that define the characteristics of the content type. Here is a list of the existing metadata interfaces with a description on the purpose of each interface and which properties they contain.

Usage 

Because some of the interfaces are optional, a recommended pattern when working with a "general" IContent instance is to use the is or as operators to check if the instance implements an interface, as in this example:

  public static CultureInfo Language(this IContent content)
        {
            if (content == null) throw new ArgumentNullException(nameof(content));
            return (content is ILocale locale) ? locale.Language : CultureInfo.InvariantCulture;
        }

public static bool IsModified(this IContent content)
        {
            if (content == null) throw new ArgumentNullException(nameof(content));
            var modifiedTrackable = content as IModifiedTrackable;
            return modifiedTrackable == null || modifiedTrackable.IsModified;
        }

Shared blocks

BlockData does not implement IContent, while shared block instances still have their own identity defined on IContent. This is accomplished so that during runtime, when a shared block instance is created (for example, through a call to IContentRepository.GetDefault<T> where T is a type inheriting from BlockData), the CMS creates a new .NET type inheriting T using a technique called mixin where the new generated subclass will implement some extra interfaces (including IContent).

That means that a shared block instance of T will implement IContent while an instance of T that is a property on a Page will not. 

IContentData

Base interface for all content models. It contains a backing PropertyDataCollection that is used when loading/saving data from database.

IContent

Base interface for all content models that can have an own identity, and hence can be loaded/saved individually. IContent inherits IContentData. Note that ContentLink.ID and ContentGuid is the same for all language branches for a content item. So the combination of ContentLink/ContentGuid and ILocale.Language uniquely specifies the content instance (given that the content implements ILocalizable). All built-in base content types, except BlockData, implement IContent. Shared block instances implement IContent (and most other metadata interfaces) at runtime.

IVersionable

An optional interface for content that supports different versions for each language branch. There can only be at most one version published at each time. All built-in types, except ContentFolder, implement IVersionable. See Content Versions for more information regarding versions.

ILocale

An optional interface for content that specifes which language a specific content instance has. All built-in types except ContentFolder implements ILocale.

ILocalizable

An optional interface for content that support multiple language branches. Inherits ILocale. All built-in types, except ContentFolder and MediaData, implement ILocalizable.

IReadOnly/IReadOnly<T>

An optional interface for content that support read-only instances. It is highly recommended that content types implement IReadOnly, which ensures the integrity of the content instances when instances are served from cache and hence reused across different requests. All built-in base content classes implement IReadOnly.

IModifiedTrackable

An optional interface for content instances that support modified tracking. There is a high performance gain during save operations if IModifiedTrackable since then only data that has actually changed needs to be persisted. All built-in base content classes implement IModifiedTrackable.

IChangeTrackable

An optional interface for content instances that support tracking of changes. All built-in base content classes implement IChangeTrackable.

IContentSecurable

An optional interface for content instances that support access checks. All built-in base content classes implement IContentSecurable.

IRoutable

An interface that content items that should be routable through a content URL should implement. All built-in base content classes, except shared blocks, implement IRoutable.

ICategorizable

An interface that content items that should be possible to categorize should implement. All built-in base content classes, except content folders, implement ICategorizable.

IInitializableContent

An optional interface that content items that can be implemented if default values should be added when a new instance of the content type is created.

IExportable

An optional interface that specifies how a content instance should be handled during export.