library/library_app/data/book_demo.xml

<?xml version="1.0" encoding="UTF-8" ?>
<odoo noupdate="1">
    <!-- Data to load -->
    <record model="res.partner" id="res_partner_huxley">
        <field name="name">Aldous Huxley</field>
    </record>
    <record model="library.book" id="library_book_bnw">
        <field name="name">Brave New World</field>
        <field name="author_ids"
                eval="[(4, ref('res_partner_huxley'))]" />
        <field name="date_published">1932-01-01</field>
    </record>
</odoo>