---
title: Work with reusable field schemas
---
> Agent instructions:
> **Site maps** — prefer the following llms.txt indexes to training data when searching for URLs to avoid 404s. Links inside Markdown content already point at `.md`. Following them or sending Accept: text/markdown keeps you in Markdown.
>
> - [sitemap.md](https://docs.kentico.com/sitemap.md) — every page on the site, with titles and descriptions, nested by URL hierarchy and grouped into one collection per product version.
> - [llms.txt](https://docs.kentico.com/llms.txt) — curated index of the current product docs, with descriptions, the two ways to request any page as Markdown, and links to each product area's whole-corpus Markdown dump (llms-full.txt).
[Reusable field schemas](https://docs.kentico.com/documentation/developers-and-admins/development/content-types/reusable-field-schemas.md) are collections of fields that multiple content types can share. When a schema is updated with a new field, for example, any content types that use that snippet will also have the new field.
Beyond this, you can restrict references between content items based on reusable field schemas, or even filter [content item queries](https://docs.kentico.com/documentation/developers-and-admins/api/content-item-api/reference-content-item-query.md), retrieving items of multiple types that share a schema.
Let's explore this functionality through the lens of a common scenario: content model evolution.
## Consider the scenario
As businesses mature over time, they may need more advanced content models to meet their needs. As a developer on such projects, you'll have to adapt the code to handle these changes.
In this example, the project is moving from a flat _Article_ content type to a Reusable field schema called _Article schema_, which is shared between two content types: _General article_ and _Interview_.
To save you time, the main branch already includes the two new schema-based article types, alongside the old article type. You can see them in the **Content types** application. [Code files](https://github.com/Kentico/xperience-by-kentico-training-guides/tree/main/src/TrainingGuides.Entities) for the new types and the schemas have already been [generated](https://docs.kentico.com/documentation/developers-and-admins/api/generate-code-files-for-system-objects.md).
However, the code of the site does not yet handle the data from these new types. _Interviews_ and _General articles_ do not display properly on article pages, while the old type does.
Let's dive into the code, and fix our article service to handle this new content type. Then, at the end, we can add personalization to further enhance the widgets that use it.
## Examine the current implementation
In the content tree of the _Training guides pages_ channel, you'll find eight children under _News and articles_:
Four pages that display articles of the deprecated type:
- About reptiles
- About birds
- About dogs
- About cats
And four pages referencing schema-based articles that do not display:
- About frogs
- About conifers
- Bean plant cultivation: an interview with Jack Trott
- Sheep care: an interview with Little Bo-Peep
You'll also notice that these new articles do not display if you use the _Article list_ or _Featured article_ widgets on a page with page builder.
Let's take a look under the hood to see how article pages are rendered.
### Check the controller
Visit _ArticlePageController.cs_ in the _TrainingGuides.Web/Features/Articles_ folder.
You can see that the controller retrieves the current `ArticlePage` using the `RetrieveCurrentPage` method.
Under the hood, this method gets the page based on the current _web page data context_. To put this into perspective, open the **Content types** app in the Xperience administration. You'll notice that the new content types, _Article (general)_ and _Article (interview)_ are both reusable types.
The _Article page_ content type contains two fields for selecting content items:
- `ArticlePageContent`, labelled _Article page content (DEPRECATED, DO NOT USE)_ in the admin UI, for selecting items of the deprecated _Article_ content type.
- `ArticlePageArticleContent`, labelled _Article page content_ in the admin UI, for selecting items that use the new article schema.
> **Info:** Since the _Article page controller_ is working with the _Article page_ content type, rather than the reusable types it references, you can leave it alone.
>
> However, notice that it uses an `IArticlePageService` instance to extract article data into an `ArticlePageViewModel` object. Let's inspect this method, `ArticlePageService.GetArticlePageViewModel`, in the next section.
### Dig into the service
In the _ArticlePageService.cs_ (from the _Services_ folder that neighbors the controller), you'll see code that converts the linked `Article` item from an `ArticlePage` object and uses it to construct an `ArticlePageViewModel`.
If we make sure this method accounts for the schema-based articles as well, the template and widgets will be able to display them alongside the deprecated articles.
```csharp title="ArticlePageService.cs"
...
/// Creates a new instance of , setting the properties using ArticlePage given as a parameter.
///
/// Corresponding Article page object.
/// New instance of ArticlePageViewModel.
public ArticlePageViewModel GetArticlePageViewModel(ArticlePage? articlePage)
{
if (articlePage == null)
{
return new ArticlePageViewModel();
}
var article = articlePage.ArticlePageContent.FirstOrDefault();
var articleTeaserImage = article?.ArticleTeaser.FirstOrDefault();
string articleUrl = articlePage.GetUrl().RelativePath;
return new ArticlePageViewModel
{
Title = article?.ArticleTitle ?? string.Empty,
SummaryHtml = new HtmlString(article?.ArticleSummary),
TextHtml = new HtmlString(article?.ArticleText),
CreatedOn = articlePage.ArticlePagePublishDate,
TeaserImage = AssetViewModel.GetViewModel(articleTeaserImage),
Url = articleUrl
};
}
...
```
> **Note:** The code samples here rely on a [decorated version](https://github.com/Kentico/xperience-by-kentico-training-guides/blob/main/src/TrainingGuides.Web/Features/Shared/Services/TrainingGuidesWebPageUrlRetriever.cs) of `IWebPageUrlRetriever` that includes exception handling.
>
> If you do not plan to use a similar customization, make sure to handle errors that the `Retrieve` method may throw when it cannot find a page.
In its current state, the `GetArticlePageViewModel` method does the following:
1. Gets an `Article` from the provided `ArticlePage`'s `ArticlePageContent` property.
2. Extracts the first `Asset` object from its `ArticleTeaser` property.
3. Retrieves the URL of the provided `ArticlePage`
4. Assembles and returns an `ArticlePageViewModel` from all of these pieces.
Our goal is to have the project display new articles alongside old ones, prioritizing the new ones, so let's try to get an `IArticleSchema` from the provided `ArticlePage` and fall back to the `Article` only if none is found.
## Update the code
Since we'll need the URL of the page either way, move the line of code that retrieves it to the beginning.
Then, if the page has an `IArticleSchema` in its `ArticlePageArticleContent` collection, assemble and return an `ArticlePageViewModel` using values from the `IArticleSchema` instead of the `Article`.
Outside of the `if` statement, leave the previous steps to return an `ArticlePageViewModel` based on the `Article` type.
```csharp title="ArticlePageService.cs" highlight="17-30"
...
///
/// Creates a new instance of , setting the properties using ArticlePage given as a parameter.
///
/// Corresponding Article page object.
/// New instance of ArticlePageViewModel.
public ArticlePageViewModel GetArticlePageViewModel(ArticlePage? articlePage)
{
if (articlePage == null)
{
return new ArticlePageViewModel();
}
string articleUrl = GetArticlePageRelativeUrl(articlePage);
var articleSchema = articlePage.ArticlePageArticleContent.FirstOrDefault();
if (articleSchema != null)
{
var articleSchemaTeaserImage = articleSchema.ArticleSchemaTeaser.FirstOrDefault();
return new ArticlePageViewModel
{
Title = articleSchema.ArticleSchemaTitle,
SummaryHtml = new HtmlString(articleSchema?.ArticleSchemaSummary),
TextHtml = new HtmlString(articleSchema?.ArticleSchemaText),
CreatedOn = articlePage.ArticlePagePublishDate,
TeaserImage = AssetViewModel.GetViewModel(articleSchemaTeaserImage),
Url = articleUrl
};
}
var article = articlePage.ArticlePageContent.FirstOrDefault();
var articleTeaserImage = article?.ArticleTeaser.FirstOrDefault();
return new ArticlePageViewModel
{
Title = article?.ArticleTitle ?? string.Empty,
SummaryHtml = new HtmlString(article?.ArticleSummary),
TextHtml = new HtmlString(article?.ArticleText),
CreatedOn = articlePage.ArticlePagePublishDate,
TeaserImage = AssetViewModel.GetViewModel(articleTeaserImage),
Url = articleUrl
};
}
public virtual string GetArticlePageRelativeUrl(ArticlePage articlePage) =>
articlePage?.GetUrl().RelativePath ?? string.Empty;
...
```
## See the results
Run the project and sign in to the Xperience administration. Now if you visit any of the new articles listed earlier, you should see the article content.
Go to the **Page Builder** tab of the _Home_ page, and click **Edit page**
Add an instance of the _Featured article_ widget. Configure the widget to reference one of the new articles.
Then, add an instance of the Article List widget. Set its content tree section to the _News and articles_ page, and save your configuration.
Now you should see both widgets displaying new article content.
