Allow disabling editing of a M2M linked item

[martin-braun]

Summary

I refer to discussion #16115. This is close to a deal breaker to me, because it causes so much confusion on the end user. Adding a linked item in a M2M field will enable editing the fields of the linked item in the relation dialog, falsy implying only this instance is edited. But if the user edits the head fields that related to the linked item, they will consequently influence the linked item where ever it has been used.

Basic Example

In the following example I have a link between a "nutrition_kit" and a "nutrition" table (M2M). In this example I pick a dataset from its M2M table from within the "nutrition_kit" form:

Here the name field is not part of the M2M table, but instead part of the "nutrition" table that is linked in my M2M table. The user will be confused, might edit the name to further specify and thus editing the "nutrition" and not this relation.

The lower form elements below the line are part of the M2M table itself and those can be edited just fine.

Motivation

It's confusing to the end user. I'm afraid someone will edit the "nutrition" and cause all relating kits to have wrong "nutrition" names. If the "nutrition" not even used multiple times in the "nutrition_kit" it will even be unnoticed. This is such a fatal flaw in my eyes.

Detailed Design

The M2M relation should provide an option to prevent editing the linked item. I could get the effect by disabling editing the field, but then I can't create or edit "nutrition" data entries obiously.

Requirements List

Must Have:

• A way to lock form entries on the linked item when editing M2M data of the relation

Drawbacks

There is little interest by the community, but please hear me out. Just because the issue won't receive enough upvotes doesn't mean that it isn't a huge roadblock. It's clearly of destructive nature when the end user is incapable of understanding the consequence of editing such fields. There is no visual guide besides a horizontal line that doesn't say anything.

Alternatives

I was trying to lock the field altogether except when creating a new "nutrition", but this doesn't work either, there is only readonly on or off, not off for new items only.

Adoption Strategy

No breaking change, the default behavior could remain as is.

Unresolved Questions

No response