Create related data and related media

Sitefinity CMS provides you with an API for managing related items using the RelatedDataExtensions public class. The API consists of extension methods over object items (facilitates the use of the API in widget templates) and over IDataItem for creating and deleting item relations.

IMPORTANT: When using the related data API, you need to work with the master versions of both the related data item and the item, to which you are creating a relation.

You can create content item relations using the following methods: 

• CreateRelation(this IDataItem item, IDataItem relatedItem, string fieldName) 
  This method creates a relation between an item and a relatedItem by field name. The item context must have a related data field with the name fieldName.

  NOTE: If there is no field with such a name, a relation is still created, even though it will not visible in Sitefinity backend. You can only access the relation via the Related data API, using the same fieldName. The above-described is generally the case when creating relations to content types not supported by the Related data field.

• CreateRelation(this IDataItem item, Guid relatedItemId, string relatedItemProviderName, string relatedItemType, string fieldName)
  This method creates a relation between an item and a related item by field name. A related item is described with the following properties: relatedItemId, relatedItemProviderName, relatedItemType.

You can delete item relations using the following methods: 

• DeleteRelation(this IDataItem item, IDataItem relatedItem, string fieldName)
  This method deletes a relation between an item and a relatedItem by field name. The item context must have a related data field with the name fieldName.
• DeleteRelation(this IDataItem item, Guid relatedItemId, string relatedItemProviderName, string relatedItemType, string fieldName)
  This method will delete a relation between item and related item by field name. Related item is described with the following properties: relatedItemId, relatedItemProviderName, relatedItemType.
• DeleteRelations(this IDataItem item)
  Deletes all relations for the current item. Both parent and child relations are removed, regardless of field names. 
• DeleteRelations(this IDataItem item, string fieldName)
  Deletes all child item relations from the particular field. 

The following code demonstrates how to create and delete item relations:

You can retrieve all related child items of particular field using the methods, listed below.

NOTE:You need to enter the accurate corresponding related field name, otherwise the returned result is null.

• IQueryable<IDataItem> GetRelatedItems(this object item, string fieldName)
  Gets child related items by field name. The method returns a query with child data items as IDataItem.
• IQueryable<T> GetRelatedItems<T>(this object item, string fieldName) where T : IDataItem 
  Generic method for getting child related items by field name. It will return a query with child data items of type T.
• int GetRelatedItemsCountByField(this object item, string fieldName = null) 
  Gets the number of related child items. Filtering by field name can be applied. 
• int GetRelatedItemsCountByType(this object item, string typeName = null)
  Gets the number of related child items. Filtering by type name can be applied.
• IEnumerable GetItemsWithSameTaxons(this object item, string itemTaxonomyFieldName, string relatedItemsTypeFullName, int skip = 0, int take = 10) 
  Returns items from a specified type with at least one matching value for the specified taxonomy field name.
• IEnumerable GetItemsWithSameTaxons(this object item, string itemTaxonomyFieldName, string relatedItemsTypeFullName, string relatedItemsTaxonomyFieldName = null, string relatedItemsProviderName = null, int skip = 0, int take = 10, string additionalFilterExpression = null, string orderExpression = null)
  Returns items from a specified type with at least one matching value for the specified taxonomy field name. Allows additional filtering to be applied

You can retrieve all parent items of particular item using the methods, listed below.

NOTE:When using the IQueryable interface, be aware that content items do not have a Provider property set, so related data is not returned. The reason is that the Provider property is a complex object and it is not persisted in the database. It is only built when you load the query from the database. When you work with the IQueryable item from the collection, the Provider property is still null. 
When the final collection is queried, you can use an IEnumerable interface to get single items from the collection.

• IQueryable<IDataItem> GetRelatedParentItems(this object item, string parentItemsTypeName, string parentItemProviderName = null, string fieldName = null)
  Gets parent related items by parent type. The method returns a query with parent data items as IDataItem. Filtering by parent item field name can be applied. In this case, field name is the name of the related field linking to this item in the parent item.
• IQueryable<T> GetRelatedParentItems<T>(this object item, string parentItemProviderName = null, string fieldName = null) where T : IDataItem 
  Gets parent related items by parent type T. The method returns a query with parent data items of type T. Filtering by parent item field name can be applied. In this case, field name is the name of the related field linking to this item, in the parent item.
• IList GetRelatedParentItemsList(this object item, string parentItemsTypeName, string parentItemProviderName = null, string fieldName = null) 
  Gets a list of all parent items of a particular item from a specific type. You can use this method when working with the widget templates. 

NOTE: The returned result contains a list with all related data items. The data items are in the same status as the related item, whose child or a parent they are.