Add documentation and source

Added documentation, source and extra files.

source/orm/library/models/book.py

@@ -0,0 +1,70 @@
+import random
+import string
+from uuid import uuid4
+
+from django.db import models
+from django.utils import timezone
+
+
+def generate_isbn() -> str:
+    """
+    Generate a random ISBN number.
+
+    Returns:
+        A 13-digit string.
+
+    """
+    digits = string.digits
+    return "".join(random.choice(digits) for _ in range(13))
+
+
+class BookQuerySet(models.QuerySet):
+    """
+    QuerySet class for books.
+
+    """
+
+    def available(self) -> models.QuerySet:
+        """
+        Get books available for a loan.
+
+        Excludes books with at least a loan whose `borrowed` field is `True`.
+        Given the constraints, only one loan for a book can have the `borrowed` status
+        to `True`.
+
+        """
+        return self.exclude(loans__borrowed=True)
+
+    def late_returns(self) -> models.QuerySet:
+        """
+        Get books that should have been returned by now.
+
+        """
+        now = timezone.now()
+        return self.filter(loans__expected_return__lt=now, borrowed=True)
+
+
+class Book(models.Model):
+    """
+    Description of a book.
+
+    """
+
+    uuid = models.UUIDField(default=uuid4, db_index=True, verbose_name="UUID")
+    isbn = models.CharField(max_length=64, default=generate_isbn, blank=False, verbose_name="ISBN")
+    name = models.CharField(max_length=128, blank=False, verbose_name="name")
+    description = models.TextField(blank=True, verbose_name="description")
+    registration_date = models.DateTimeField(auto_now_add=True, verbose_name="creation date")
+    year = models.PositiveIntegerField(default=1950, null=True, db_index=True, verbose_name="published")
+    authors = models.ManyToManyField("library.Author", related_name="books", verbose_name="authors")
+    genre = models.ForeignKey(
+        "library.Genre", on_delete=models.SET_NULL, null=True, related_name="books", verbose_name="genre"
+    )
+    objects = BookQuerySet.as_manager()
+
+    class Meta:
+        verbose_name = "book"
+        verbose_name_plural = "books"
+
+    def __str__(self):
+        return f"{self.name} ({self.isbn})"