Add `foreign_key_exists?` method.

2 files changed, 27 insertions, 0 deletions

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 7eaa89c9a7..a70d93c28b 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -650,6 +650,10 @@ module ActiveRecord
       def foreign_key(*args) # :nodoc:
         @base.add_foreign_key(name, *args)
       end
+      
+      def foreign_key_exists?(*args) # :nodoc:
+        @base.foreign_key_exists?(name, *args)
+      end
 
       private
         def native
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 f905669a24..0ca8570d00 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -671,6 +671,29 @@ module ActiveRecord
       def foreign_keys(table_name)
         raise NotImplementedError, "foreign_keys is not implemented"
       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 = {})
+        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
+        
+        foreign_keys(from_table).any? {|fk| options.keys.all? {|key| fk.options[key].to_s == options[key].to_s } }
+      end
 
       # Adds a new foreign key. +from_table+ is the table with the key column,
       # +to_table+ contains the referenced primary key.