library/library_app/models/res_partner.py

from odoo import fields, models

class Partner(models.Model):
    _inherit = 'res.partner'
    published_book_ids = fields.One2many(
        'library.book', #related model
        'publisher_id', #fields for 'this' on related model
        string = 'Published Books'
    )
    book_ids = fields.Many2many(
        'library.book',string = 'Authored Books'
    )