Offer Tag Merging

[rtpg]

Basically there are times where you want to say "I have Tag A and Tag B, let's have only Tag A". This would involve rewriting any TagItems and friends that are using Tag B to instead point to Tag A (and at the very end probably delete Tag B?)

Ideas of what we could offer:

• a Python function like tag_b.merge_into(tag_a) (this would make tag A the canonical one)
• a Django management command that could be used to do this merging
• Something in the Admin where we could click on a tag, then say to merge that tag into another one

I think there's gotta be some functions like "find django objects that refer to this object", given that the Django Admin lists related items on delete...

[rtpg]

(#470 is related to this)

[Trafire]

Was using this as a way to explore the library this morning, Maybe something like this would work?

Idea here is provide a base_name and either get or create a tag with that base name.

Find all existing case insensitive versions of that tag, and update the to use the one that matches base_name. Then delete all the other tags.

from taggit.models import Tag, TaggedItem


def update_vs_delete_tags(base_tag_name):
    """
    Identifies tags that are duplicates of the base_tag_name case insensitive value.
    
    Ignores any duplicate values.
        
    """
    duplicate_tags = Tag.objects.filter(name__iexact=base_tag_name).exclude(tag__name=base_tag_name)
    existing_items = set(TaggedItem.objects.filter(tag__name=base_tag_name).values_list("object_id", "content_type_id"))
    to_update = []
    tagged_items = TaggedItem.objects.filter(tag__in=duplicate_tags)
    for tagged_item in tagged_items:
        comparison = (tagged_item.object_id, tagged_item.content_type_id)
        if comparison not in existing_items:
            to_update.append(tagged_item.id)
        existing_items.add(comparison)
    return to_update


def merge_case_insensitive_tags(base_tag_name):
    to_update = update_vs_delete_tags(base_tag_name)
    base_tag, _ = Tag.objects.get_or_create(name=base_tag_name)
    TaggedItem.objects.filter(tag__in=to_update).update(
        tag_id=base_tag.id
    )
    # Remove All Tags that are now redundant
    Tag.objects.filter(name__iexact=base_tag_name).exclude(tag__name=base_tag_name).delete()