many2one_uom

A plain many2one on a unit field would happily offer kilograms for a service or dozens for a liquid. This widget exists so that never happens: it is the standard many2one with its autocomplete swapped for a unit-aware one that knows the product on the line.

The wiring is visible in the source. The widget reads two sibling fields on the record, the product (default product_id) and the quantity (default product_uom_qty), resolves the product model, and hands all of it to the replacement autocomplete. When the record is a product (product template or variant forms), it uses the record itself as the product context.

Under Odoo 19's reworked unit system, where packagings became units carrying a relative factor to a reference unit, that context is what lets the dropdown offer entries like a 12-pack alongside Units for one product and only sensible units for another.

Unit mistakes are expensive in a way most data errors are not: a purchase line in units that should have been cases is a real truck with the wrong quantity on it. The fix is not training people to be careful; it is a dropdown that only offers units that make sense for the product at hand, which is precisely this widget's job.

It matters double under Odoo 19's unit overhaul. Packagings are no longer a separate concept bolted onto lines; they are units with a factor, and this widget is where users meet them. Selling by the pack while stocking by the unit works out of the box when the dropdown understands the product; it becomes a support queue when a plain many2one lets any unit through.

If your business runs on hours and days instead of boxes, note the naming collision only: that widget handles time encoding and is unrelated to this one.

How core order lines use it

<field name="product_uom_id" widget="many2one_uom"/>

Defaults do the work: the widget finds product_id and product_uom_qty on the same line.

Custom line model with different field names

<field name="uom_id" widget="many2one_uom"
       options="{'product_field': 'item_id', 'quantity_field': 'qty'}"/>

Point the two options at your model's product and quantity fields and the unit dropdown becomes product-aware on your custom lines too.

Locked to existing units

<field name="product_uom_id" widget="many2one_uom"
       options="{'no_create': True}"/>

The inherited many2one options apply unchanged; here creation is blocked so typos cannot mint new units, usually the right call outside the configuration screens.

Two source details are worth carrying into any customization built on this widget.

The override is explicitly temporary. The file opens with a developer note: the autocomplete extension "will be removed in the future when the autocomplete source generation come from a hook". The widget name and options are the stable contract; the internal component layout is not. JavaScript patches on UomMany2One internals are the kind of customization that dies at the next major version, so keep any behavior change at the options/domain level if you possibly can.

Product resolution has a special case. On most models the product comes from product_field, but when the record itself is a product.template or product.product, the source uses the record's own id as the product. That is why the same widget works on product forms without any options, and why a custom wrapper model around products may need explicit options where core forms need none.

Odoo 20 is expected at Odoo Experience in Brussels, 24 to 26 September 2026. The changes below are read from the public development branch and are not final until release.

Options and registration are unchanged: the same two own options over the same inherited set. The temporary-override note still stands in the development branch, so the promised hook-based replacement has not landed yet; when it does, XML stays stable while JavaScript patches on the internals break. We re-verify once Odoo 20 ships.