Hi everyone,

If you need to enable multiple selection inside a One2many field, there is a module called "One2many Checkbox Widget" (for Odoo 17) available on the Odoo Apps store.

After installation, you can use it directly in your form view like this:

<field name="your_one2many_field" widget="one2many_checkbox"/>

This will add checkboxes for each line, allow selecting/deselecting all at once, and make the selected IDs accessible in the backend using:

self._context.get("selected_ids", [])

It’s a simple way to handle multi-selection in One2many fields.

Let me explain better. As you can see at the bottom of the image, the one2many field is shown as a tree view. However when user clicks on "Add item" a new row show up with text fields to add. But instead of text field I want it to be a list of all items from database so that user can only select from the list instead of a empty field. I tried adding widget="selection" but then I get an empty selection box.

<record id="iventiva_invoice_parameter_location_form" model="ir.ui.view">
    <field name="model">account.invoice.parameter</field>
    <field name="inherit_id" ref="iventiva_account_invoicing.account_invoice_parameter_form"/>
    <field name="arch" type="xml">
        <xpath expr="//sheet" position="inside">
            <group string="Assigned Locationsssrrr">
                <field name="stock_location_ids" nolabel="1">
                    <tree editable="bottom">
                        <field name="name" widget="selection"/>
                    </tree>
                </field>
            </group>
        </xpath>
    </field>
</record>