fk: infere column name from table names.

This allows to create and remove foreign keys without specifying a column.

activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb

@@ -647,10 +647,11 @@ module ActiveRecord
       end
 
       def add_foreign_key(from_table, to_table, options = {})
+        options[:column] ||= foreign_key_column_for(to_table)
         primary_key = options.fetch(:primary_key, "id")
 
         options = {
-          column: options.fetch(:column),
+          column: options[:column],
           primary_key: primary_key,
           name: foreign_key_name(from_table, options),
           dependent: options.fetch(:dependent, nil)
@@ -661,17 +662,26 @@ module ActiveRecord
         execute schema_creation.accept at
       end
 
-      def remove_foreign_key(from_table, options = {})
+      def remove_foreign_key(from_table, options_or_to_table = {})
+        if options_or_to_table.is_a?(Hash)
+          options = options_or_to_table
+        else
+          options = { column: foreign_key_column_for(options_or_to_table) }
+        end
+
         at = create_alter_table from_table
         at.drop_foreign_key foreign_key_name(from_table, options)
 
         execute schema_creation.accept at
       end
 
+      def foreign_key_column_for(table_name) # :nodoc:
+        "#{table_name.to_s.singularize}_id"
+      end
+
       def foreign_key_name(table_name, options) # :nodoc:
         options.fetch(:name) do
-          column_name = options.fetch(:column)
-          "#{table_name}_#{column_name}_fk"
+          "#{table_name}_#{options.fetch(:column)}_fk"
         end
       end
 

activerecord/lib/active_record/migration/command_recorder.rb

@@ -170,13 +170,15 @@ module ActiveRecord
       end
 
       def invert_add_foreign_key(args)
-        from_table, _to_table, add_options = *args
+        from_table, to_table, add_options = *args
         add_options ||= {}
 
         if add_options[:name]
           options = {name: add_options[:name]}
         elsif add_options[:column]
           options = {column: add_options[:column]}
+        else
+          options = to_table
         end
 
         [:remove_foreign_key, [from_table, options]]

activerecord/test/cases/migration/command_recorder_test.rb

@@ -271,6 +271,11 @@ module ActiveRecord
         assert_equal [:enable_extension, ['uuid-ossp'], nil], enable
       end
 
+      def test_invert_add_foreign_key
+        enable = @recorder.inverse_of :add_foreign_key, [:dogs, :people]
+        assert_equal [:remove_foreign_key, [:dogs, :people]], enable
+      end
+
       def test_invert_add_foreign_key_with_column
         enable = @recorder.inverse_of :add_foreign_key, [:dogs, :people, column: "owner_id"]
         assert_equal [:remove_foreign_key, [:dogs, column: "owner_id"]], enable

activerecord/test/cases/migration/foreign_key_test.rb

@@ -46,7 +46,21 @@ module ActiveRecord
         assert_equal "fk_name", fk.name
       end
 
-      def test_add_foreign_key
+      def test_add_foreign_key_inferes_column
+        @connection.add_foreign_key :astronauts, :rockets
+
+        foreign_keys = @connection.foreign_keys("astronauts")
+        assert_equal 1, foreign_keys.size
+
+        fk = foreign_keys.first
+        assert_equal "astronauts", fk.from_table
+        assert_equal "rockets", fk.to_table
+        assert_equal "rocket_id", fk.column
+        assert_equal "id", fk.primary_key
+        assert_equal "astronauts_rocket_id_fk", fk.name
+      end
+
+      def test_add_foreign_key_with_column
         @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id"
 
         foreign_keys = @connection.foreign_keys("astronauts")
@@ -112,7 +126,15 @@ module ActiveRecord
         assert_equal :nullify, fk.dependent
       end
 
-      def test_remove_foreign_key
+      def test_remove_foreign_key_inferes_column
+        @connection.add_foreign_key :astronauts, :rockets
+
+        assert_equal 1, @connection.foreign_keys("astronauts").size
+        @connection.remove_foreign_key :astronauts, :rockets
+        assert_equal [], @connection.foreign_keys("astronauts")
+      end
+
+      def test_remove_foreign_key_by_column
         @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id"
 
         assert_equal 1, @connection.foreign_keys("astronauts").size