Performance: Request cache referenced entities when saving documents with block editors

[AndyButland]

Description

This PR is part of ongoing efforts to improve validation, save and publish time for Umbraco setups using lots of blocks and languages. There are two updates related to save here:

• Added request cache for content and media references in multi URL picker
• Added block list "pre-caching" of referenced content and media in media picker and multi URL picker

The latter introduces a new interface that ICacheReferencedEntities property editor DataValueEditors can optionally implement. If they do, they can parse the provided list of values from a block editor that they know how to handle, to in one go get all the referenced entities they need. They can then make one database request to get and cache them in the request cache, such that they are available later when needed in the save process.

In my artificially throttled test setup - using a database from a site with lots of blocks and languages, hosted in Azure whilst I'm working locally - I'm seeing 200% improvements for the save operation when triggered from the backoffice or management API.

To caveat, the publish part still takes quite some time - but this, plus the previous PRs that focussed on the validate and publish steps - #20405 and #20485 - should produce some noticeable improvement.

Testing

Verify content save operations continue to work. Using breakpoints e.g. in MediaPicker3PropertyEditor you can check that referenced entities are cached and retrieved from the cache when needed.

[Copilot]

Pull Request Overview

This PR improves save and publish performance for Umbraco instances with extensive block editor usage by implementing a request caching strategy for referenced entities. The changes introduce a new ICacheReferencedEntities interface that property editors can implement to batch-fetch and cache referenced content and media items in a single database operation, reducing redundant lookups during save operations.

Key changes:

• Added ICacheReferencedEntities interface for property editors to implement batch caching of referenced entities
• Implemented request caching in MultiUrlPickerValueEditor and MediaPicker3PropertyValueEditor for content and media references
• Added protected helper methods in DataValueEditor base class for cached entity retrieval

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Umbraco.Core/PropertyEditors/ICacheReferencedEntities.cs	New interface defining contract for batch caching of referenced entities in block values
src/Umbraco.Core/PropertyEditors/DataValueEditor.cs	Added protected helper methods for cached content/media retrieval and cache presence checking
src/Umbraco.Infrastructure/PropertyEditors/BlockValuePropertyValueEditorBase.cs	Added method to invoke entity caching for all property values within block editor data
src/Umbraco.Infrastructure/PropertyEditors/BlockEditorPropertyValueEditor.cs	Integrated entity caching invocation before processing block editor values
src/Umbraco.Infrastructure/PropertyEditors/MediaPicker3PropertyEditor.cs	Implemented ICacheReferencedEntities interface and migrated to shared caching helpers
src/Umbraco.Infrastructure/PropertyEditors/MultiUrlPickerValueEditor.cs	Implemented ICacheReferencedEntities interface and added request caching for content/media lookups
tests/Umbraco.Tests.UnitTests/Umbraco.Core/PropertyEditors/Validators/MultiUrlPickerValueEditorValidationTests.cs	Updated test to provide required AppCaches parameter for new constructor

[AndyButland]

Checks for availability of request cache have been added @kjac (also reviewed and updated as necessary from the two linked PRs above).

[AndyButland]

Have cherry-picked this and labelled for 16.4. Let's discuss on Monday whether this will also go in 17.0 or 17.1.

[AndyButland]

Cherry-picked now too for 17.0.