To find the books, you need to perform the following steps:

1. Add the find_book method in the library.book model:

def find_book(self): 
    ...

2. Write the search domain for your criteria:

domain = [
    '|',
        '&', ('name', 'ilike', 'Book Name'),
             ('category_id.name', 'ilike', 'Category Name'),
        '&', ('name', 'ilike', 'Book Name 2'),
             ('category_id.name', 'ilike', 'Category Name 2')
]

3. Call the search() method with the domain, which will return the recordset:

books = self.search(domain)