added unique constraint on RecipeBookEntry table

Signed-off-by: Tobias Lindenberg <tobias@lindenberg.pm>

cookbook/migrations/0096_auto_20210109_2044.py

@@ -0,0 +1,31 @@
+# Generated by Django 3.1.5 on 2021-01-09 19:44
+
+from django.db import migrations
+
+
+def delete_duplicate_bookmarks(apps, schema_editor):
+    """
+    In this migration, a unique constraint is set on the fields `recipe` and `book`.
+    If there are already duplicate entries, the migration will fail.
+    Therefore all duplicate entries are deleted beforehand.
+    """
+    RecipeBookEntry = apps.get_model('cookbook', 'RecipeBookEntry')
+
+    for row in RecipeBookEntry.objects.all():
+        if RecipeBookEntry.objects.filter(recipe=row.recipe, book=row.book).count() > 1:
+            row.delete()
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ('cookbook', '0095_auto_20210107_1804'),
+    ]
+
+    operations = [
+        # run function to delete duplicated bookmarks
+        migrations.RunPython(delete_duplicate_bookmarks),
+        migrations.AlterUniqueTogether(
+            name='recipebookentry',
+            unique_together={('recipe', 'book')},
+        ),
+    ]

cookbook/models.py

@@ -265,6 +265,9 @@ class RecipeBookEntry(models.Model):
     def __str__(self):
         return self.recipe.name
 
+    class Meta:
+        unique_together = (('recipe', 'book'),)
+
 
 class MealType(models.Model):
     name = models.CharField(max_length=128)

cookbook/views/views.py

@@ -7,6 +7,7 @@ from django.contrib.auth import update_session_auth_hash, authenticate
 from django.contrib.auth.forms import PasswordChangeForm
 from django.contrib.auth.password_validation import validate_password
 from django.core.exceptions import ValidationError
+from django.db import IntegrityError
 from django.db.models import Q, Avg
 from django.http import HttpResponseRedirect
 from django.shortcuts import render, get_object_or_404
@@ -105,9 +106,13 @@ def recipe_view(request, pk, share=None):
             bookmark.recipe = recipe
             bookmark.book = bookmark_form.cleaned_data['book']
 
-            bookmark.save()
-
-            messages.add_message(request, messages.SUCCESS, _('Bookmark saved!'))
+            try:
+                bookmark.save()
+            except IntegrityError as e:
+                if 'UNIQUE constraint' in str(e.args):
+                    messages.add_message(request, messages.ERROR, _('This recipe is already linked to the book!'))
+            else:
+                messages.add_message(request, messages.SUCCESS, _('Bookmark saved!'))
 
     comment_form = CommentForm()
     bookmark_form = RecipeBookEntryForm()