backend/app/models/tag.rb

@@ -23,6 +23,8 @@ class Tag < ApplicationRecord
   has_many :parents, through: :reversed_tag_implications, source: :parent_tag
 
   has_many :tag_similarities, dependent: :delete_all
+  has_many :tag_similarities_as_target,
+           class_name: 'TagSimilarity', foreign_key: :target_tag_id, dependent: :delete_all
 
   has_many :deerjikists, dependent: :delete_all
 
@@ -140,7 +142,7 @@ class Tag < ApplicationRecord
     retry
   end
 
-  def self.merge_tags target_tag, source_tags
+  def self.merge_tags! target_tag, source_tags
     target_tag => Tag
 
     Tag.transaction do
@@ -166,6 +168,8 @@ class Tag < ApplicationRecord
       end
     end
 
+    target_tag.update!(post_count: PostTag.kept.where(tag: target_tag).count)
+
     target_tag
   end
 

backend/spec/models/tag_spec.rb

@@ -1,7 +1,7 @@
 require 'rails_helper'
 
 RSpec.describe Tag, type: :model do
-  describe '.merge_tags' do
+  describe '.merge_tags!' do
     let!(:target_tag) { create(:tag) }
     let!(:source_tag) { create(:tag) }
 
@@ -11,7 +11,7 @@ RSpec.describe Tag, type: :model do
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
 
       it 'moves the post_tag, deletes the source tag, and aliases the source tag_name' do
-        described_class.merge_tags(target_tag, [source_tag])
+        described_class.merge_tags!(target_tag, [source_tag])
 
         expect(source_post_tag.reload.tag_id).to eq(target_tag.id)
         expect(Tag.exists?(source_tag.id)).to be(false)
@@ -24,7 +24,7 @@ RSpec.describe Tag, type: :model do
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
 
       it 'discards the duplicate source post_tag and keeps one active target post_tag' do
-        described_class.merge_tags(target_tag, [source_tag])
+        described_class.merge_tags!(target_tag, [source_tag])
 
         active = PostTag.kept.where(post_id: post_record.id, tag_id: target_tag.id)
         discarded_source = PostTag.with_discarded.find(source_post_tag.id)
@@ -40,7 +40,7 @@ RSpec.describe Tag, type: :model do
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
 
       it 'ignores the target tag in source_tags' do
-        described_class.merge_tags(target_tag, [source_tag, target_tag])
+        described_class.merge_tags!(target_tag, [source_tag, target_tag])
 
         expect(Tag.exists?(target_tag.id)).to be(true)
         expect(Tag.exists?(source_tag.id)).to be(false)
@@ -59,7 +59,7 @@ RSpec.describe Tag, type: :model do
 
       it 'rolls back the transaction' do
         expect {
-          described_class.merge_tags(target_tag, [source_tag])
+          described_class.merge_tags!(target_tag, [source_tag])
         }.to raise_error(ActiveRecord::RecordInvalid)
 
         expect(Tag.exists?(source_tag.id)).to be(true)