--- title: Filter content with taxonomies --- > 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). ## Implement the filtering Now, we can implement filtering based on the _Article category_ taxonomy. ### Add new widget property First, let's add a [tag selector](https://docs.kentico.com/documentation/developers-and-admins/customization/extend-the-administration-interface/ui-form-components/reference-admin-ui-form-components.md#tag-selector) to the widget UI so that editors can select the desired tags. Find the definition of the [Article list widget properties](https://github.com/Kentico/xperience-by-kentico-training-guides/blob/main/src/TrainingGuides.Web/Features/Articles/Widgets/ArticleList/ArticleListWidgetProperties.cs) in the Training guides repository. Add a new `IEnumerable` property called `Tags` between the existing `ContentTreeSection` and `TopN`. Decorate the property with `TagSelectorComponent` attribute. Specify allowed taxonomy passing our taxonomy code name, `ArticleCategory`, as the first parameter. > **Tip:** To refresh your memory on defining widget properties revisit our [Build a simple call-to-action widget](https://docs.kentico.com/guides/development/page-builder/build-simple-cta-widget.md#define-widget-properties) guide. ```csharp title="ArticleListWidgetProperties.cs" // ... existing code ... public class ArticleListWidgetProperties : IWidgetProperties { [ContentItemSelectorComponent( [ ArticlePage.CONTENT_TYPE_NAME, DownloadsPage.CONTENT_TYPE_NAME, EmptyPage.CONTENT_TYPE_NAME, LandingPage.CONTENT_TYPE_NAME, ServicePage.CONTENT_TYPE_NAME ], Label = "Select a parent page to pull articles from", AllowContentItemCreation = false, MaximumItems = 1, Order = 10)] public IEnumerable ContentTreeSection { get; set; } = []; // new property definition [TagSelectorComponent( "ArticleCategory", Label = "Filter to categories", ExplanationText = "Select 0, 1 or more Article Type tags. Shows all if none are selected", Order = 15)] public IEnumerable Tags { get; set; } = []; // ... existing code ... } // ... existing code ... ``` Run the project and navigate to Page Builder mode of any page that contains Article list widget. In the widget configuration you should see the new tag selector control allowing you to pick **Animals** or **Plants** tags. 🎬 [Video](https://docs.kentico.com/docsassets/modules/filter-content-with-taxonomies/new-tag-selector.mp4) ### Adjust widget view component Now, let's add some logic to the widget view component. It needs to account for the tags the editor has chosen when retrieving content. Take a look at the [ArticleListWidgetViewComponent.cs](https://github.com/Kentico/xperience-by-kentico-training-guides/blob/main/src/TrainingGuides.Web/Features/Articles/Widgets/ArticleList/ArticleListWidgetViewComponent.cs) file. The `InvokeAsync` method calls `RetrieveArticlePages` to fetch the relevant article pages from the Content hub, passing in the editor's content tree selection. Then, it orders and further filters the articles before constructing a view model and returning the widget view. ```csharp title="ArticleListWidgetViewComponent.cs - old implementation" // ... existing code ... public async Task InvokeAsync(ArticleListWidgetProperties properties) { var model = new ArticleListWidgetViewModel(); if (properties.ContentTreeSection.Any()) { var articlePages = await RetrieveArticlePages(properties.ContentTreeSection.First()); model.Articles = (properties.OrderBy.Equals("OldestFirst", StringComparison.OrdinalIgnoreCase) ? GetArticlePageViewModels(articlePages).OrderBy(article => article.CreatedOn) : GetArticlePageViewModels(articlePages).OrderByDescending(article => article.CreatedOn)) .Take(properties.TopN) .ToList(); model.CtaText = properties.CtaText; } return View("~/Features/Articles/Widgets/ArticleList/ArticleListWidget.cshtml", model); } // ... existing code ... ``` We'll adjust the private method `RetrieveArticlePages` to consider the new `Tags` property in the following way: ```csharp title="ArticleListWidgetViewComponent.cs" // ... existing code ... // Add IEnumerable of tag references as a new parameter private async Task> RetrieveArticlePages(ContentItemReference parentPageSelection, IEnumerable tags) { var selectedPageGuid = parentPageSelection.Identifier; var selectedPage = selectedPageGuid != Guid.Empty ? await contentItemRetrieverService.RetrieveWebPageByContentItemGuid(selectedPageGuid) : null; string selectedPagePath = selectedPage?.SystemFields.WebPageItemTreePath ?? string.Empty; if (string.IsNullOrEmpty(selectedPagePath)) { return []; } // if no tags are specified, retrieve the Article pages in the same way as before if (!tags.Any()) { return await contentItemRetrieverService.RetrieveWebPageChildrenByPath( selectedPagePath, 3); } // otherwise process the tags and retrieve the appropriate pages accordingly else { // code to retrieve article pages based on tags will go here } } // ... existing code ... ``` Now there is one issue we need to solve: Our widget expects **Article page** content items to construct its view model. However, the property holding our taxonomy tags is on the reusable content item linked by the page. Because of the current limitations of the [ContentRetriever API](https://docs.kentico.com/documentation/developers-and-admins/api/content-item-api/content-retriever-api.md), we will do this in two steps: 1. Retrieve the IDs of all reusable content items that implement **Article schema** and contain the specified tags. 2. Retrieve **Article page** content items on the specified path that link these reusable items. ### Implement the service methods Let's go implement these service methods in our [ContentItemRetrieverService.cs file](https://github.com/Kentico/xperience-by-kentico-training-guides/blob/main/src/TrainingGuides.Web/Features/Shared/Services/ContentItemRetrieverService.cs). #### Retrieve reusable content items by schema and tags The ContentRetriever API has a [`RetrieveContentOfReusableSchemas` extension method](https://docs.kentico.com/documentation/developers-and-admins/api/content-item-api/reference-content-retriever-api.md#retrieve-content-items-sharing-reusable-field-schema) that is exactly suited for our scenario. We will utilize it to retrieve the reusable content items that contain: - Our _Article schema_, passing in the schema codename as a parameter (`schemaName`) - GUIDs of specific tags, using the [WhereContainsTags](https://docs.kentico.com/documentation/developers-and-admins/api/content-item-api/reference-content-item-query.md#wherecontainstags) extension method. The data we need to perform this query will become additional method parameters: - the name of the database column where we expect to find the tags (`taxonomyColumnName`) - the GUIDs of the required tags (`tagGuids`) - whether to map fields specific to each content type (`includeContentTypeFields`) - the content's language (`languageName`) Declare the method in the `IContentItemRetrieverService` interface and implement it in the `ContentItemRetrieverService` class. ```csharp title="IContentItemRetrieverService.cs" using CMS.ContentEngine; using Kentico.Content.Web.Mvc; namespace TrainingGuides.Web.Features.Shared.Services; public interface IContentItemRetrieverService { // ... existing code ... Task> RetrieveContentItemsBySchemaAndTags( string schemaName, string taxonomyColumnName, IEnumerable tagGuids, bool includeContentTypeFields = true, string? languageName = null); // ... existing code ... } ``` ```csharp title="ContentItemRetrieverService.cs" using CMS.ContentEngine; using CMS.Websites.Routing; using Kentico.Content.Web.Mvc; using Kentico.Content.Web.Mvc.Routing; namespace TrainingGuides.Web.Features.Shared.Services; public class ContentItemRetrieverService : IContentItemRetrieverService { // ... existing code ... /// public async Task> RetrieveContentItemsBySchemaAndTags( string schemaName, string taxonomyColumnName, IEnumerable tagGuids, bool includeContentTypeFields = true, string? languageName = null) { var parameters = new RetrieveContentOfReusableSchemasParameters { LanguageName = languageName ?? preferredLanguageRetriever.Get(), IsForPreview = webSiteChannelContext.IsPreview, IncludeContentTypeFields = includeContentTypeFields, }; return await contentRetriever.RetrieveContentOfReusableSchemas( [schemaName], parameters, query => query.Where(where => where.WhereContainsTags(taxonomyColumnName, tagGuids)), RetrievalCacheSettings.CacheDisabled, configureModel: null); } // ... existing code ... } ``` #### Retrieve Article pages by path and reference Next, we need a method that will fetch all child Article pages on a specific path **which also link any of specified reusable content items**. Let's implement a new public method in the `ContentItemRetrieverService` class that retrieves pages from a given path which link to the specified content items. This method needs two new parameters beyond the existing path and depth: the **code name of the reference field** and the **IEnumerable of content item IDs**. Call `RetrieveWebPageChildrenByPath` method and pass in custom query configuration - an anonymous function calling the [Linking](https://docs.kentico.com/documentation/developers-and-admins/api/content-item-api/reference-content-item-query.md#linking) extension method. ```csharp title="ContentItemRetrieverService.cs" using CMS.ContentEngine; using CMS.Websites.Routing; using Kentico.Content.Web.Mvc; using Kentico.Content.Web.Mvc.Routing; namespace TrainingGuides.Web.Features.Shared.Services; public class ContentItemRetrieverService : IContentItemRetrieverService { // ... existing code ... public async Task> RetrieveWebPageChildrenByPathAndReference( string parentPagePath, string referenceFieldName, IEnumerable referenceIds, int depth = 1, string? languageName = null) where T : IWebPageFieldsSource, new() => await RetrieveWebPageChildrenByPath( path: parentPagePath, depth: depth, additionalQueryConfiguration: config => config.Linking(referenceFieldName, referenceIds), languageName: languageName); // ... existing code ... } // ... existing code ... ``` > **Note:** **Page security** > > You may notice some methods in the content item retriever service, including `RetrieveWebPageChildrenByPath`, have a parameter called `includeSecuredItems`. > > This parameter relates to [registration and authentication](https://docs.kentico.com/documentation/developers-and-admins/development/registration-and-authentication.md), determining whether to filter out content items for which a visitor does not have permissions. > > We've left it out of this example, but you can see security integrated into `RetrieveWebPageChildrenByPathAndReference` and the article list widget in the [finished branch](https://github.com/Kentico/xperience-by-kentico-training-guides/tree/finished/) of the Training guides repo. > > Our [membership guides](https://docs.kentico.com/guides/development/members.md) cover the supporting implementation that enables registration, authentication, and secured pages. Remember to also declare the new method in the `IContentItemRetrieverService` interface. ```csharp title="IContentItemRetrieverService.cs" using CMS.ContentEngine; using Kentico.Content.Web.Mvc; namespace TrainingGuides.Web.Features.Shared.Services; public interface IContentItemRetrieverService { // ... existing code ... Task> RetrieveWebPageChildrenByPathAndReference( string parentPagePath, string referenceFieldName, IEnumerable referenceIds, int depth = 1, string? languageName = null) where T : IWebPageFieldsSource, new(); // ... existing code ... } // ... existing code ... ``` > **Info:** See the full [ContentItemRetrieverService.cs](https://github.com/Kentico/xperience-by-kentico-training-guides/blob/finished/src/TrainingGuides.Web/Features/Shared/Services/ContentItemRetrieverService.cs) and [IContentItemRetrieverService.cs](https://github.com/Kentico/xperience-by-kentico-training-guides/blob/finished/src/TrainingGuides.Web/Features/Shared/Services/IContentItemRetrieverService.cs) files in the finished branch of our Training guides repo. ### Put it all together Our backend work is done. Let's utilize the new methods in the _ArticleListWidgetViewComponent_. Find the empty `else` statement inside the `RetrieveArticlePages` method. Add logic for the case when the editor **did** specify the tags to filter by: ```csharp title="ArticleListWidgetViewComponent.cs" // ... existing code ... private async Task> RetrieveArticlePages(ContentItemReference parentPageSelection, IEnumerable tags) { // ... existing code ... else { // first extract the list of tag GUIDs var tagGuids = tags.Select(tag => tag.Identifier).ToList(); // retrieve the IDs of Article schema reusable content items // to specify the schema, use the REUSABLE_FIELD_SCHEMA_NAME constant from the generated IArticleSchema interface // pass in the name of the ArticleSchemaCategory field // we only use the content item ID here, so skip mapping content type fields var taggedArticleIds = ( await contentItemRetrieverService.RetrieveContentItemsBySchemaAndTags( IArticleSchema.REUSABLE_FIELD_SCHEMA_NAME, nameof(IArticleSchema.ArticleSchemaCategory), tagGuids, includeContentTypeFields: false) ).Select(article => article.SystemFields.ContentItemID); // retrieve and return Article page content items on specified path that reference the reusable content items // pass in the name of the ArticlePageArticleContent field, which we use to link reusable article item to Article page return await contentItemRetrieverService.RetrieveWebPageChildrenByPathAndReference( selectedPagePath, nameof(ArticlePage.ArticlePageArticleContent), taggedArticleIds, depth: 3); } } // ... existing code ... ``` > **Note:** **Why skip content type fields?** > > This code only reads `SystemFields.ContentItemID` from the retrieved items, so mapping per-content-type fields would produce data that it immediately discards. Passing `includeContentTypeFields: false` sets the underlying [`IncludeContentTypeFields` property](https://docs.kentico.com/documentation/developers-and-admins/api/content-item-api/reference-content-retriever-api.md#page-query-parameters) to `false`, limiting the query to data common to all results: content item metadata, reusable field schema fields, and page URL data. This improves query performance, most noticeably when retrieving items that share a reusable field schema, as we do here. > **Info:** **Content querying approach** > > You'll notice that this code first queries the IDs of reusable items associated with the tags, then queries pages that link to those items. > > Depending on the number of tagged reusable items and pages in your project, this two-query approach may be faster or slower than retrieving all children of the provided page and filtering them after retrieval, for example, with [LINQ](https://learn.microsoft.com/en-us/dotnet/csharp/linq/). > > The approach demonstrated here works better with [paging](https://docs.kentico.com/documentation/developers-and-admins/api/content-item-api/content-retriever-api.md#optional-query-configuration) functionality, allowing consistent page counts per batch, while a LINQ approach requires fewer database queries. > > In either case, we strongly recommend that you implement [caching](https://docs.kentico.com/documentation/developers-and-admins/api/content-item-api/content-retriever-api.md#implicit-result-caching) in production scenarios. Finally, call the updated `RetrieveArticlePages` method from `InvokeAsync` to retrieve the article pages. ```csharp title="ArticleListWidgetViewComponent.cs" // ... existing code ... public async Task InvokeAsync(ArticleListWidgetProperties properties) { var model = new ArticleListWidgetViewModel(); if (properties.ContentTreeSection.Any()) { // call the updated method passing in the Tags property var articlePages = await RetrieveArticlePages(properties.ContentTreeSection.First(), properties.Tags); model.Articles = (properties.OrderBy.Equals("OldestFirst", StringComparison.OrdinalIgnoreCase) ? GetArticlePageViewModels(articlePages).OrderBy(article => article.CreatedOn) : GetArticlePageViewModels(articlePages).OrderByDescending(article => article.CreatedOn)) .Take(properties.TopN) .ToList(); model.CtaText = properties.CtaText; } return View("~/Features/Articles/Widgets/ArticleList/ArticleListWidget.cshtml", model); } // ... existing code ... ``` ## See the results Rebuild and run your project. Navigate to a page (e.g., _Home_) where you added the Article list widget. Configure the widget to show articles with different tags, and see the filtered results when you **Apply** the changes. 🎬 [Video](https://docs.kentico.com/docsassets/modules/filter-content-with-taxonomies/filter-articles-finished.mp4) Find the complete and working implementation of this example in the [finished branch of the Training guides repository](https://github.com/Kentico/xperience-by-kentico-training-guides/tree/finished). The repository version of the widget also incorporates membership functionality.