Infer foerign_key when inverse_of is present (#47797)

* Infer `foerign_key` when `inverse_of` is present

Automatically infer `foreign_key` on `has_one` and `has_many` associations when `inverse_of` is present.

When inverse of is present, rails has all the info it needs to figure out what the foreign_key on the associated model should be.  I can't imagine this breaking anything

* Update test models to remove redundant foreign_keys

* add changelog entry

* fix changelog grammar

Co-authored-by: Rafael Mendonça França <rafael@franca.dev>

activerecord/CHANGELOG.md

@@ -1,3 +1,19 @@
+*   Infer `foerign_key` when `inverse_of` is present on `has_one` and `has_many` associations.
+
+    ```ruby
+    has_many :citations, foreign_key: "book1_id", inverse_of: :book
+    ```
+
+    can be simplified to
+
+    ```ruby
+    has_many :citations, inverse_of: :book
+    ```
+
+    and the foreign_key will be read from the corresponding `belongs_to` association.
+
+    *Daniel Whitney*
+
 *   Limit max length of auto generated index names
 
     Auto generated index names are now limited to 62 bytes, which fits within

activerecord/lib/active_record/reflection.rb

@@ -731,6 +731,8 @@ def derive_foreign_key
             "#{name}_id"
           elsif options[:as]
             "#{options[:as]}_id"
+          elsif options[:inverse_of]
+            inverse_of.foreign_key
           else
             active_record.model_name.to_s.foreign_key
           end

activerecord/test/models/book.rb

@@ -4,7 +4,7 @@ class Book < ActiveRecord::Base
   belongs_to :author
   belongs_to :format_record, polymorphic: true
 
-  has_many :citations, foreign_key: "book1_id", inverse_of: :book
+  has_many :citations, inverse_of: :book
   has_many :references, -> { distinct }, through: :citations, source: :reference_of
 
   has_many :subscriptions

activerecord/test/models/comment.rb

@@ -23,7 +23,7 @@ class Comment < ActiveRecord::Base
   belongs_to :first_post, foreign_key: :post_id
   belongs_to :special_post_with_default_scope, foreign_key: :post_id
 
-  has_many :children, class_name: "Comment", foreign_key: :parent_id, inverse_of: :parent
+  has_many :children, class_name: "Comment", inverse_of: :parent
   belongs_to :parent, class_name: "Comment", counter_cache: :children_count, inverse_of: :children
 
   alias_attribute :entry, :post

activerecord/test/models/company.rb

@@ -58,7 +58,7 @@ class Firm < Company
   has_many :unsorted_clients, class_name: "Client"
   has_many :unsorted_clients_with_symbol, class_name: :Client
   has_many :clients_sorted_desc, -> { order "id DESC" }, class_name: "Client"
-  has_many :clients_of_firm, -> { order "id" }, foreign_key: "client_of", class_name: "Client", inverse_of: :firm
+  has_many :clients_of_firm, -> { order "id" }, class_name: "Client", inverse_of: :firm
   has_many :clients_ordered_by_name, -> { order "name" }, class_name: "Client"
   has_many :unvalidated_clients_of_firm, foreign_key: "client_of", class_name: "Client", validate: false
   has_many :dependent_clients_of_firm, -> { order "id" }, foreign_key: "client_of", class_name: "Client", dependent: :destroy

activerecord/test/models/human.rb

@@ -4,7 +4,7 @@ class Human < ActiveRecord::Base
   self.table_name = "humans"
 
   has_one :face, inverse_of: :human
-  has_one :autosave_face, class_name: "Face", autosave: true, foreign_key: :human_id, inverse_of: :autosave_human
+  has_one :autosave_face, class_name: "Face", autosave: true, inverse_of: :autosave_human
   has_one :polymorphic_face, class_name: "Face", as: :polymorphic_human, inverse_of: :polymorphic_human
   has_one :polymorphic_face_without_inverse, class_name: "Face", as: :poly_human_without_inverse
   has_many :interests, inverse_of: :human

activerecord/test/models/pirate.rb

@@ -98,7 +98,7 @@ class DestructivePirate < Pirate
 
 class FamousPirate < ActiveRecord::Base
   self.table_name = "pirates"
-  has_many :famous_ships, inverse_of: :famous_pirate, foreign_key: :pirate_id
+  has_many :famous_ships, inverse_of: :famous_pirate
   validates_presence_of :catchphrase, on: :conference
 end
 

activerecord/test/models/ship.rb

@@ -24,7 +24,7 @@ def cancel_save_callback_method
 
 class ShipWithoutNestedAttributes < ActiveRecord::Base
   self.table_name = "ships"
-  has_many :prisoners, inverse_of: :ship, foreign_key: :ship_id
+  has_many :prisoners, inverse_of: :ship
   has_many :parts, class_name: "ShipPart", foreign_key: :ship_id
 
   validates :name, presence: true, if: -> { true }

activerecord/test/models/topic.rb

@@ -46,7 +46,7 @@ def two
     end
   end
 
-  has_many :replies, dependent: :destroy, foreign_key: "parent_id", autosave: true, inverse_of: :topic
+  has_many :replies, dependent: :destroy, autosave: true, inverse_of: :topic
   has_many :approved_replies, -> { approved }, class_name: "Reply", foreign_key: "parent_id", counter_cache: "replies_count"
   has_many :open_replies, -> { open }, class_name: "Reply", foreign_key: "parent_id"
 

activerecord/test/models/zine.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 class Zine < ActiveRecord::Base
-  has_many :interests, inverse_of: :zine, foreign_key: "zine_id"
+  has_many :interests, inverse_of: :zine
 end