cooperative-market/beesdoo_account/views/account_invoice.xml

<openerp>
	<data>
		<record model="ir.ui.view" id="beesdoo_account_invoice_form_view">
			<field name="name">beesdoo.account.invoice.form.view</field>
			<field name="model">account.invoice</field>
			<field name="inherit_id" ref="account.invoice_form" />
			<field name="arch" type="xml">
				<field name="date_invoice" position="attributes">
					<attribute name="required">True</attribute>
				</field>
			</field>
		</record>
	</data>

	<data>
		<record model="ir.ui.view" id="beesdoo_account_invoice_supplier_form_view">
			<field name="name">beesdoo.account.invoice.supplier.form.view</field>
			<field name="model">account.invoice</field>
			<field name="inherit_id" ref="account.invoice_supplier_form" />
			<field name="arch" type="xml">
				<field name="date_invoice" position="attributes">
					<attribute name="required">True</attribute>
				</field>
			</field>
		</record>
	</data>

</openerp>