Block preview shows wrong content for blocks using AssignedContentItem in blueprint editor

[deanleigh]

Which Umbraco.Community.BlockPreview version are you using?

5.3.2

Which Umbraco version are you using? For example: 10.4.0 - don't just write v10

17.1.0

Bug summary

When editing a Document Blueprint in Settings > Document Blueprints, blocks that read from the parent document via Umbraco.AssignedContentItem display content from a random existing published page instead of the blueprint's own property values.

For example, a block that renders @currentPage.PageTitle shows "The Moorish Treasures of Andalucía" (from an existing published page) instead of [Page Title] (the blueprint's actual stored value).

Blocks with their own self-contained content (e.g. Rich Text Editor blocks) render correctly. The issue only affects blocks that reach "upward" to the parent document for their data via AssignedContentItem.

The created document from the blueprint has the correct values — this is a preview-only issue.

Steps to reproduce

1. Create a document type (e.g. "Tailored Tour") with a block grid property and page-level properties (pageTitle, pageDescription)
2. Create a block grid element type (e.g. "Feature - Page Title and Description") with no stored properties — its Razor partial reads from Umbraco.AssignedContentItem:

   @{
       if (Umbraco.AssignedContentItem is not IContentHeadingDefault currentPage) return;
   }
   <h1>@currentPage.PageTitle</h1>
   <p>@currentPage.PageDescription</p>

3. Create a real content page of that document type with pageTitle = "The Moorish Treasures of Andalucia"
4. Create a Document Blueprint of the same type with pageTitle = "[Page Title]" (placeholder text)
5. Add the block to the blueprint's block grid
6. Expected: Block grid preview shows "[Page Title]"
7. Actual: Block grid preview shows "The Moorish Treasures of Andalucia" (from the existing content page)

The issue is in the AssignedContentItem resolution chain in UmbracoViewPage.cs:

1. View model is BlockGridItem (not IPublishedContent) — skipped
2. View model is not IContentModel — skipped
3. Fallback: UmbracoContext.PublishedRequest.PublishedContent — resolves to an existing published page, not the blueprint
   Blueprints have IsBlueprint = true and are not in the published content cache. The fallback in step 3 picks up whatever was last in the published request context.

Expected result / actual result

When editing a Document Blueprint, the block grid SSR preview should resolve Umbraco.AssignedContentItem to the blueprint content, allowing blocks to read the blueprint's own property values.

[deanleigh]

Additional findings from further testing (Umbraco 17.1.0, BlockPreview 5.3.2)

We've been doing more testing around this and wanted to share what we found in case it's helpful.

Test 1: Copying blocks between content nodes
We copied the block grid from one published Tailored Tour ("Flemish Masters – Bruges, Antwerp and Ghent") into a brand new, empty content node. The Block Preview rendered the title as "The Moorish Treasures of Andalucía" — a completely different published page. The copied blocks themselves had the correct Flemish Masters data when clicked into, but the preview was pulling from elsewhere.

Test 2: Blueprint creation and verification
We created a template content node with placeholder values ([Page Title], [Page Description], etc.) and saved it as a Document Blueprint multiple times — including after clearing the memory cache, restarting the site, publishing the node, and using different blueprint names. Each time, the blueprint preview showed "The Moorish Treasures of Andalucía" instead of the placeholder text.

We initially thought the blueprint data was being saved incorrectly, and spent a fair amount of time investigating before realising the stored data was actually correct all along. We confirmed this by using the blueprint with our content creation pipeline — the created document had all the correct placeholder structure and values. Sort Mode also showed the correct block types and layout.

Test 3: Blocks with no stored properties
The "Page Title and Description" block has no editable properties of its own — it renders entirely from parent properties via AssignedContentItem. Clicking "Edit" on the block in the blueprint confirms this (it shows "No Configuration — No configuration required"). So there's no way to visually verify the blueprint content for these blocks without Sort Mode or actually creating a document from it.

Observations:

• The fallback content isn't consistent — it seems to pick up whichever published page of the same document type was last in the request context
• The issue occurs not just in the blueprint editor but also when viewing blocks on unpublished content nodes and during block copy operations
• For blocks that store their own content (Rich Text Editor blocks, etc.), the preview renders correctly — it's specifically blocks using AssignedContentItem that are affected

Workaround we're using: Sort Mode to verify block structure in blueprints, and trusting that the underlying data is correct even though the preview shows wrong content.

Is it worth me forking it and taking a look at my end or does that description ring any bells when we made Blueprints previewable?

[deanleigh]

Quick clarification: This isn't blueprint-specific. We see the same behaviour on brand new pages created from the document type (not from a blueprint), on existing pages, and when copying blocks between pages. Any block using AssignedContentItem shows content from another page regardless of context.

Code-level finding: The issue is in BlockPreviewApiController.cs, method GetPublishedContent(). When context.Content?.GetById(nodeKey) returns null (blueprints, unsaved pages), it falls back to:

_documentCacheService.GetByContentType(publishedContentType).FirstOrDefault()

This grabs the first available published page of the same document type and passes it to SetupPublishedRequest(), which sets it as PublishedRequest.PublishedContent — and that's what UmbracoViewPage resolves as AssignedContentItem.