added functions in author and books model

nishaespera_reading/bookshelf/admin.py

 from django.contrib import admin
 
-# Register your models here.

nishaespera_reading/bookshelf/models.py

@@ -10,7 +10,10 @@ class Author(models.Model):
     nationality = models.CharField(max_length = 50)
     bio = models.TextField(max_length = 700)
 
-def require_int(value):
+    def __str__(self):
+        return self.first_name + ' ' + self.last_name
+
+def verify_int(value):
     if value.isdigit() == False:
         raise ValidationError('ISBN must only be integers.')
     
@@ -18,11 +21,13 @@ class Books(models.Model):
     title = models.CharField(max_length = 70)
     author = models.ForeignKey(Author, on_delete = models.CASCADE)
     publisher = models.CharField(max_length = 70)
-    year_published = models.IntegerField(null = True,
-        validators=[MinValueValidator(1400), MaxValueValidator(datetime.now().year)]
+    year_published = models.IntegerField(null = True, blank = True,
+        validators=[MinValueValidator(1000), MaxValueValidator(datetime.now().year)]
         )
-    ISBN = models.CharField(max_length = 13, validators = [MinValueValidator(13), require_int])
-    blurb = models.CharField(min_length = 100, max_length = 200)
+    ISBN = models.CharField(max_length = 13, validators = [MinValueValidator(13), verify_int])
+    blurb = models.CharField(max_length = 200, validators = [MinValueValidator(100)])
+    def __str__(self):
+        return self.title