refactors tag model to fit ordered collection structure

bookwyrm/models/tag.py

@@ -5,16 +5,19 @@ from django.db import models
 
 from bookwyrm import activitypub
 from bookwyrm.settings import DOMAIN
-from .base_model import OrderedCollectionMixin, BookWyrmModel
+from .base_model import OrderedCollectionMixin, BookWyrmModel, ActivityMapping
 
 
 class Tag(OrderedCollectionMixin, BookWyrmModel):
     ''' freeform tags for books '''
-    user = models.ForeignKey('User', on_delete=models.PROTECT)
-    book = models.ForeignKey('Edition', on_delete=models.PROTECT)
-    name = models.CharField(max_length=100)
+    name = models.CharField(max_length=100, unique=True)
     identifier = models.CharField(max_length=100)
 
+    activity_mappings = [
+        ActivityMapping('id', 'remote_id'),
+        ActivityMapping('name', 'name'),
+    ]
+
     @classmethod
     def book_queryset(cls, identifier):
         ''' county of books associated with this tag '''
@@ -30,6 +33,30 @@ class Tag(OrderedCollectionMixin, BookWyrmModel):
         base_path = 'https://%s' % DOMAIN
         return '%s/tag/%s' % (base_path, self.identifier)
 
+
+    def save(self, *args, **kwargs):
+        ''' create a url-safe lookup key for the tag '''
+        if not self.id:
+            # add identifiers to new tags
+            self.identifier = urllib.parse.quote_plus(self.name)
+        super().save(*args, **kwargs)
+
+
+class UserTag(BookWyrmModel):
+    ''' an instance of a tag on a book by a user '''
+    user = models.ForeignKey('User', on_delete=models.PROTECT)
+    book = models.ForeignKey('Edition', on_delete=models.PROTECT)
+    tag = models.ForeignKey('Tag', on_delete=models.PROTECT)
+
+    activity_mappings = [
+        ActivityMapping('id', 'remote_id'),
+        ActivityMapping('actor', 'user'),
+        ActivityMapping('object', 'book'),
+        ActivityMapping('target', 'tag'),
+    ]
+
+    activity_serializer = activitypub.AddBook
+
     def to_add_activity(self, user):
         ''' AP for shelving a book'''
         return activitypub.Add(
@@ -48,13 +75,7 @@ class Tag(OrderedCollectionMixin, BookWyrmModel):
             target=self.to_activity(),
         ).serialize()
 
-    def save(self, *args, **kwargs):
-        ''' create a url-safe lookup key for the tag '''
-        if not self.id:
-            # add identifiers to new tags
-            self.identifier = urllib.parse.quote_plus(self.name)
-        super().save(*args, **kwargs)
 
     class Meta:
         ''' unqiueness constraint '''
-        unique_together = ('user', 'book', 'name')
+        unique_together = ('user', 'book', 'tag')