partner-contact/partner_contact_department/views/res_partner_view.xml

<?xml version="1.0" encoding="utf-8"?>

<flectra>

    <record model="ir.ui.view" id="view_partner_form_department">
        <field name="name">Partner form with department</field>
        <field name="model">res.partner</field>
        <field name="inherit_id" ref="base.view_partner_form"/>
        <field name="arch" type="xml">
            <xpath expr="//sheet/group//field[@name='function']" position="after">
                <field name="department_id"
                       placeholder="Department"
                       attrs="{'invisible': [('is_company','=', True)]}"
                       options='{"no_open": True}'/>
            </xpath>
            <xpath expr="//field[@name='child_ids']/form//field[@name='function']"
                   position="after">
                <field name="is_company" invisible="True"/>
                <field name="department_id"
                       placeholder="Department"
                       attrs="{'invisible': [('is_company','=', True)]}"
                       options='{"no_open": True}'/>
            </xpath>
        </field>
    </record>

    <record model="ir.ui.view" id="view_res_partner_filter_department">
        <field name="name">Partner search with department</field>
        <field name="model">res.partner</field>
        <field name="inherit_id" ref="base.view_res_partner_filter"/>
        <field name="arch" type="xml">
            <field name="category_id" position="after">
                <field name="department_id"/>
            </field>
            <filter name="salesperson" position="after">
                <filter name="department"
                        string="Department"
                        domain="[('is_company', '=', False)]"
                        context="{'group_by': 'department_id'}"/>
            </filter>
        </field>
    </record>

</flectra>