Merge pull request #18662 from estum/foreign-key-exists

Add `foreign_key_exists?` method.

4 files changed, 63 insertions, 15 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index e1cace7d88..ff8dd6b72d 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Add `foreign_key_exists?` method.
+
+    *Tõnis Simo*
+
 *   Use SQL COUNT and LIMIT 1 queries for `none?` and `one?` methods if no block or limit is given,
     instead of loading the entire collection to memory.
     This applies to relations (e.g. `User.all`) as well as associations (e.g. `account.users`)
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index 8cd4b8e5b2..a2777fcd0a 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -50,6 +50,14 @@ module ActiveRecord
         options[:primary_key] != default_primary_key
       end
 
+      def defined_for?(options_or_to_table = {})
+        if options_or_to_table.is_a?(Hash)
+          options_or_to_table.all? {|key, value| options[key].to_s == value.to_s }
+        else
+          to_table == options_or_to_table.to_s
+        end
+      end
+
       private
       def default_primary_key
         "id"
@@ -651,6 +659,10 @@ module ActiveRecord
         @base.add_foreign_key(name, *args)
       end
 
+      def foreign_key_exists?(*args) # :nodoc:
+        @base.foreign_key_exists?(name, *args)
+      end
+
       private
         def native
           @base.native_database_types
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 8217468024..0438c95bd7 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -757,21 +757,7 @@ module ActiveRecord
       def remove_foreign_key(from_table, options_or_to_table = {})
         return unless supports_foreign_keys?
 
-        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
-
-        fk_name_to_delete = options.fetch(:name) do
-          fk_to_delete = foreign_keys(from_table).detect {|fk| fk.column == options[:column].to_s }
-
-          if fk_to_delete
-            fk_to_delete.name
-          else
-            raise ArgumentError, "Table '#{from_table}' has no foreign key on column '#{options[:column]}'"
-          end
-        end
+        fk_name_to_delete = foreign_key_for!(from_table, options_or_to_table).name
 
         at = create_alter_table from_table
         at.drop_foreign_key fk_name_to_delete
@@ -779,6 +765,31 @@ module ActiveRecord
         execute schema_creation.accept(at)
       end
 
+      # Checks to see if a foreign key exists on a table for a given foreign key definition.
+      #
+      #   # Check a foreign key exists
+      #   foreign_key_exists?(:accounts, :branches)
+      #
+      #   # Check a foreign key on specified column exists
+      #   foreign_key_exists?(:accounts, column: :owner_id)
+      #
+      #   # Check a foreign key with a custom name exists
+      #   foreign_key_exists?(:accounts, name: "special_fk_name")
+      #
+      def foreign_key_exists?(from_table, options_or_to_table = {})
+        foreign_key_for(from_table, options_or_to_table).present?
+      end
+
+      def foreign_key_for(from_table, options_or_to_table = {}) # :nodoc:
+        return unless supports_foreign_keys?
+        foreign_keys(from_table).detect {|fk| fk.defined_for? options_or_to_table }
+      end
+
+      def foreign_key_for!(from_table, options_or_to_table = {}) # :nodoc:
+        foreign_key_for(from_table, options_or_to_table) or \
+          raise ArgumentError, "Table '#{from_table}' has no foreign key for #{options_or_to_table}"
+      end
+
       def foreign_key_column_for(table_name) # :nodoc:
         "#{table_name.to_s.singularize}_id"
       end
diff --git a/activerecord/test/cases/migration/foreign_key_test.rb b/activerecord/test/cases/migration/foreign_key_test.rb
index b2f2d077eb..7f4790bf3e 100644
--- a/activerecord/test/cases/migration/foreign_key_test.rb
+++ b/activerecord/test/cases/migration/foreign_key_test.rb
@@ -147,6 +147,27 @@ module ActiveRecord
         assert_equal :nullify, fk.on_update
       end
 
+      def test_foreign_key_exists
+        @connection.add_foreign_key :astronauts, :rockets
+
+        assert @connection.foreign_key_exists?(:astronauts, :rockets)
+        assert_not @connection.foreign_key_exists?(:astronauts, :stars)
+      end
+
+      def test_foreign_key_exists_by_column
+        @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id"
+
+        assert @connection.foreign_key_exists?(:astronauts, column: "rocket_id")
+        assert_not @connection.foreign_key_exists?(:astronauts, column: "star_id")
+      end
+
+      def test_foreign_key_exists_by_name
+        @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", name: "fancy_named_fk"
+
+        assert @connection.foreign_key_exists?(:astronauts, name: "fancy_named_fk")
+        assert_not @connection.foreign_key_exists?(:astronauts, name: "other_fancy_named_fk")
+      end
+
       def test_remove_foreign_key_inferes_column
         @connection.add_foreign_key :astronauts, :rockets