many2many_barcode_tags

Barcodes have to be unique. That is enforced in the database, which means an attempt to create a second record with an existing barcode comes back as a constraint violation rather than as a friendly validation message.

Odoo's tags widget lets you create a new record by typing a value and pressing enter, a quick create. When a quick create fails, the standard behavior is to assume the typed value was not enough information and to open a full creation dialog instead, so the user can fill in what was missing.

For a duplicate barcode that is exactly wrong. Nothing was missing; the value simply cannot be used. Opening a dialog invites the user to try again with the same barcode and fail again, this time with a less clear error. This widget changes that one case: a uniqueness violation is rethrown, so the user sees the failure rather than a dialog.

Barcode uniqueness is the sort of constraint that only matters when it is violated, and then it matters a lot: two units of measure sharing a barcode means a scan is ambiguous, and ambiguity in a warehouse becomes a mispick.

The interface lesson is more general than barcodes. Falling back to a creation dialog on any failure is a reasonable default, but it assumes every failure is about incomplete data. Where a constraint is the likely cause, that assumption turns a clear error into a confusing loop, and the fix is to let the specific error through.

The core usage

<field name="barcode_ids"
       widget="many2many_barcode_tags"/>

No options. The only difference from plain tags is what happens when a quick create fails.

Preventing quick create entirely

<field name="barcode_ids"
       widget="many2many_barcode_tags"
       options="{'no_quick_create': True}"/>

Inherited from the tags widget. A stricter answer where barcodes should only be created through their own form.

The plain tags widget

<field name="barcode_ids" widget="many2many_tags"/>

Same rendering, but a duplicate barcode opens a creation dialog rather than surfacing the error.

The widget is two small classes. The first extends the tags dropdown's autocomplete and overrides the method that handles a failed quick create. It inspects the error for the database driver's uniqueness violation marker and, if it finds it, rethrows. Anything else is passed to the parent implementation, which does the usual thing and offers a creation dialog.

The second class extends the tags field and swaps in that autocomplete. The registration spreads the tags descriptor and adds a styling class, so the field keeps the standard tags appearance.

The detail worth being precise about is where the check looks. It reads the debug information attached to the error and tests it for the constraint name the database driver produces. That is a string test against a server error payload, which is pragmatic rather than principled: it works because Odoo forwards that payload, and it would stop working if the payload were suppressed, at which point the widget would silently behave like plain tags.

Note also what the widget does not do. It does not produce a friendlier message, translate the constraint into business language, or prevent the attempt. It only stops the error being converted into a dialog, so what the user sees is Odoo's standard error presentation for a constraint violation.

Odoo 20 is expected at Odoo Experience in Brussels, 24 to 26 September 2026. The development branch is unstable and this may still change; we re-verify the page after release.

Byte-identical. The file on the development branch matches Odoo 19 exactly, including the debug payload test. Nothing about this widget changes in Odoo 20.