after migration J3 -> J6: all events missing in frontend

Hi guys, I was asked to update an old Joomla 3 site to Joomla 6. It was quite an adventure with JEM, since I had to adjust quit a lit of tables manually (a lot of duplicate table errors during the update process).

The main thing now is that non of the events is  displayed in the front end, not in Simplelist not in amy modules. I opened  and saved them in backend, I created a new event, used the default template, – nothing ... (template overrides are disabled).

Any further ideas how to get them back?

Tell me the JEM version in J3.
What was the jump version of JEM during the migration to J6?
What was the first error of JEM, and in what version?

is there any web to check?
I need more info.

Start point: JEM 2.3.6 in J3, all JEM extensions deactivated
then:

• updated to J4
  updated to JEM 4.5 (here quite some db errors)
• updated to J5
  updated to JEM 5.0.1
• updated to J6

Only then, I realized that the events do not show up in the front end. Categories and venues are ok and do show up.
Everything else looks fine – all events, categories and venues are there in the backend.

Just thinking:  for not showing up it will probably be to due to an error or a setting. .
- are you able to debug or check for database table error?  turning on debugging on a live website is a thing but maybe copy database/tables local and test it there.
- as you said you adjusted tables. perhaps it's good to check if those are inline but guess you already did that. 
- did you also try to create a new event with new venue + new category


- 

You migrated directly from JEM 2.3.6 to JEM 4.5.0. The problem is that JEM 4.5.0 no longer includes some of the old SQL update files needed to migrate the database structure from JEM 2.3.x.

That could explain why the events are still there in the backend but you get "No events" in the frontend: the database migration may be incomplete.

I would go back to the backup before installing JEM 4.5.0 and try this path:

Joomla 3 + JEM 2.3.6
→ migrate to Joomla 4
→ install JEM 4.4.2
→ check that JEM works correctly and that the events are visible in the frontend
→ migrate to Joomla 5 (JEM 4.4.2 is compatible with J5)
→ update to JEM 5.0.1
→ check everything again
→ migrate to Joomla 6

You don't need JEM 4.5.0 for this migration. 4.5.0 was mainly intended for users staying on Joomla 4 who wanted some of the newer JEM functionality before moving to Joomla 5/6.

I wouldn't modify or recreate the events yet. I think the event data is probably OK and the issue is in the database migration. Check the structure events table.

Try 2.3.6 → 4.4.2 first and check the frontend before continuing. If the events appear there, we'll know we've found the problem.

I checked the JEM 4.5.0 code and I think I've found the problem.

The 4.5.0 installer allows the upgrade from JEM 2.3.6. There is no minimum JEM version check in `preflight()`, so 2.3.6 → 4.5.0 is accepted.

However, there is a gap in the SQL migration chain.

JEM 4.4.2 contains:

2.3.13.sql – 2.3.17.sql  
4.0b2.sql  
4.0b4.sql  
4.1.0.sql onwards

JEM 4.5.0 starts at:

4.1.0.sql

So 4.5.0 accepts an upgrade from 2.3.6 but no longer contains the SQL files required to bring the old 2.3.x schema up to the 4.x schema.

This could explain the current state: the component works and the events are visible in the backend, but the frontend query returns "No events".

I see two possible fixes in JEM:

1. Restore the legacy SQL migration files in 4.5.0 and officially support 2.3.6 → 4.5.0.

2. Add a minimum-version check to the 4.5.0 `preflight()` and reject upgrades from versions for which the complete SQL migration chain is no longer included.

For your current installation, there are also two options.

The clean one is to restore the backup and repeat:

J3 + JEM 2.3.6  
→ J4 + JEM 4.4.2  
→ verify BE/FE  
→ J5 + JEM 4.4.2  
→ JEM 5.0.1  
→ verify again  
→ J6

Alternatively, before rolling everything back, we could try repairing the current database.

On a backup/copy, apply the missing SQL migrations from the 4.4.2 package:

2.3.13.sql  
2.3.14.sql  
2.3.15.sql  
2.3.16.sql  
2.3.17.sql  
4.0b2.sql  
4.0b4.sql

Then check the schema/version state and determine which of the 4.1.x → 4.5.0 migrations have already been executed by Joomla before applying anything else.

I wouldn't blindly rerun 4.1.0 onwards because some of those migrations may already have been applied during the 4.5.0 installation and could fail with duplicate columns/indexes.

Actually, testing the missing 2.3.x/4.0 SQL chain on a copy of the current database could be useful: if the frontend events start working afterwards, we would have a reproducible confirmation of the migration bug.