Umbraco 17 → 18: How should existing content be migrated before backward compatibility is removed

Questions
1

Umbraco 17 → 18: How should existing Block List/Block Grid content be migrated?

We are currently upgrading an Umbraco installation from Umbraco 17 to Umbraco 18 and would like some clarification regarding the expected content migration path.

Background

Our upgrade history is somewhat unusual:

  • We have upgraded the database with each Umbraco version from 13 through 17.

  • During those upgrades, the database did not contain our actual content.

  • We used Umbraco Deploy to move the content from 13 to 17

  • From Umbraco 17 onwards, the database contains the actual content.

  • We are now upgrading from Umbraco 17 to 18 with existing content in the database.

What we have observed

After upgrading to Umbraco 18, we have found that some existing Block List content no longer works correctly.

Our understanding is that Umbraco 17 still contains backwards-compatible code for handling older Block List data structures, while this backwards compatibility has been removed in Umbraco 18.

We have confirmed this issue with Block List content.

We have not yet confirmed the same issue with Block Grid, but we suspect it may also be relevant. We have found migration plans/documentation related to Block Grid in earlier Umbraco versions, including Umbraco 15, which makes us unsure whether all existing content needs to go through a similar migration process before upgrading to 18.

Our question

We are considering running an automated Playwright script against all content while still running Umbraco 17.

The script would open and save/publish the content in order to trigger any migrations that Umbraco 17 performs when content is saved.

However, we don’t know whether this is sufficient.

Specifically:

  1. Is opening and saving existing content in Umbraco 17 a supported way of migrating old Block List data to the format expected by Umbraco 18?

  2. Does saving the content trigger all necessary migrations, or are there migrations that need to be run separately?

  3. Does the same apply to Block Grid, and should we assume that existing Block Grid content also needs to be migrated before upgrading to Umbraco 18?

  4. Are there other property editors or content types that we should check for the same type of backwards-compatibility removal?

  5. Is there an official migration plan or recommended procedure that we should follow before upgrading the database/application to Umbraco 18?

  6. Given our upgrade history, where the database was upgraded through versions 13–17 without the actual content present and the content was moved using Umbraco Deploy, are there any additional migration considerations we should take into account?

What we would like to establish

Before proceeding further, we would like to establish whether the following is a safe and supported upgrade path:

Umbraco 17 → migrate/save all existing content → Umbraco 18

Or whether we should perform a dedicated content migration before upgrading to Umbraco 18.

Any guidance on the officially supported approach would be greatly appreciated.

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