many2one_reference

A many2one_reference field stores an integer id whose model is not fixed. The model name lives in a companion field, declared on the Python side as model_field. Together they point at any record in the database.

This widget makes that pair usable. It reads the model name out of the companion field, hands it to the standard Many2One component as the relation, and lets the user search and pick a record exactly as they would on an ordinary many2one.

It declares no options. Its extractProps simply delegates to the shared many2one extractor, so it inherits that widget's prop handling rather than defining its own.

You meet this on models that attach to anything: an activity, a log entry, an attachment, a data-cleaning record. One record has to reference a sales order today and a contact tomorrow, and a fixed relation cannot express that.

For users the experience should be invisible. They pick a type, then they pick a record. What they must not see is a form that fails to open, which is exactly what happens when the view is built wrong, so the next section is worth reading before you put one of these on a screen.

The companion field must be present in the view. It can be invisible, but it must be there:

<field name="res_model" invisible="1"/>
<field name="res_id" widget="many2one_reference"/>

This is the version that breaks the form:

<!-- res_model is not in the view: the widget throws on render -->
<field name="res_id" widget="many2one_reference"/>

On the Python side, the pairing is declared on the field itself:

res_id = fields.Many2oneReference("Record", model_field="res_model")

Most Odoo widgets fail softly. This one does not, and the code says so explicitly:

get relation() {
    const modelField = this.props.record.fields[this.props.name].model_field;
    if (!(modelField in this.props.record.data)) {
        throw new Error(`Many2OneReferenceField: model_field must be in view (${modelField})`);
    }
    return this.props.record.data[modelField];
}

The getter runs on every render, so the error surfaces the moment the form paints. The user sees a broken view, not a missing field. The message names the field it wanted, which makes the fix obvious once you find the message, and the place to find it is the browser console.

The same getter drives a quieter behavior worth knowing. The props passed down include:

readonly: this.props.readonly || !relation,

So when the companion field is present but empty, the picker renders readonly rather than throwing. A user who has not yet chosen a model cannot type into the record field at all. That is deliberate, since there is nothing to search yet, but it reads as a disabled field with no explanation. If your form puts the record field above the model field, users will hit it constantly. Put the model field first.

No change. Diffing the many2one_reference registration between the 19.0 and 20.0 branches shows no options added or removed, no registration changes and the same supported type.

The component is rewritten internally for OWL 3, as every widget in Odoo 20 is, but nothing about how you use it from a view changes.