#419

backend/app/models/external_tag.rb

@@ -6,8 +6,13 @@ class ExternalTag < ApplicationRecord
   has_many :posts, through: :post_external_tags
 
   has_many :nico_tag_versions, foreign_key: :tag_id, inverse_of: :external_tag
-  has_many :nico_tag_relations, foreign_key: :tag_id, dependent: :destroy
-  has_many :linked_tags, through: :nico_tag_relations, source: :nico_tag
+
+  has_many :nico_tag_relations,
+           foreign_key: :nico_tag_id,
+           inverse_of: :nico_tag,
+           dependent: :destroy
+
+  has_many :linked_tags, through: :nico_tag_relations, source: :tag
 
   def snapshot_linked_tag_names
     linked_tags.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')

backend/app/models/nico_tag_relation.rb

@@ -1,6 +1,9 @@
 class NicoTagRelation < ApplicationRecord
-  belongs_to :nico_tag, class_name: 'Tag'
-  belongs_to :tag, class_name: 'Tag'
+  belongs_to :nico_tag,
+             class_name: 'ExternalTag',
+             foreign_key: :nico_tag_id,
+             inverse_of: :nico_tag_relations
+  belongs_to :tag, class_name: 'Tag', foreign_key: :tag_id
 
   validates :nico_tag_id, presence: true
   validates :tag_id, presence: true

backend/app/models/tag.rb

@@ -28,8 +28,11 @@ class Tag < ApplicationRecord
   has_many :post_tags, inverse_of: :tag
   has_many :posts, through: :post_tags
 
-  has_many :nico_tag_relations, foreign_key: :nico_tag_id, dependent: :destroy
-  has_many :linked_tags, through: :nico_tag_relations, source: :tag
+  has_many :reversed_nico_tag_relations,
+           class_name: 'NicoTagRelation',
+           foreign_key: :nico_tag_id,
+           dependent: :destroy
+  has_many :linked_nico_tags, through: :reversed_nico_tag_relations, source: :nico_tag
 
   has_many :tag_implications, foreign_key: :parent_tag_id, dependent: :destroy
   has_many :children, through: :tag_implications, source: :tag