fk: use random digest names

The name of the foreign key is not relevant from a users perspective.
Using random names resolves the urge to rename the foreign key when the
respective table or column is renamed.

4 files changed, 36 insertions, 13 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
index e495304376..5d13ee3633 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
@@ -30,7 +30,7 @@ FOREIGN KEY (#{quote_column_name(o.column)})
         end
 
         def visit_DropForeignKey(name)
-          "DROP CONSTRAINT #{name}"
+          "DROP CONSTRAINT #{quote_column_name(name)}"
         end
 
         private
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 2e47e68754..785cfd9dbc 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -35,7 +35,7 @@ module ActiveRecord
       end
 
       def primary_key
-        options[:primary_key]
+        options[:primary_key] || default_primary_key
       end
 
       def on_delete
@@ -45,6 +45,15 @@ module ActiveRecord
       def on_update
         options[:on_update]
       end
+
+      def custom_primary_key?
+        options[:primary_key] != default_primary_key
+      end
+
+      private
+      def default_primary_key
+        "id"
+      end
     end
 
     # Represents the schema of an SQL table in an abstract way. This class
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 4da42717c1..e203767992 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -650,11 +650,10 @@ module ActiveRecord
         return unless supports_foreign_keys?
 
         options[:column] ||= foreign_key_column_for(to_table)
-        primary_key = options.fetch(:primary_key, "id")
 
         options = {
           column: options[:column],
-          primary_key: primary_key,
+          primary_key: options[:primary_key],
           name: foreign_key_name(from_table, options),
           on_delete: options[:on_delete],
           on_update: options[:on_update]
@@ -674,8 +673,17 @@ module ActiveRecord
           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] }
+          if fk_to_delete
+            fk_to_delete.name
+          else
+            raise ArgumentError, "Table '#{from_table}' has no foreign key on column '#{options[:column]}'"
+          end
+        end
+
         at = create_alter_table from_table
-        at.drop_foreign_key foreign_key_name(from_table, options)
+        at.drop_foreign_key fk_name_to_delete
 
         execute schema_creation.accept at
       end
@@ -686,11 +694,7 @@ module ActiveRecord
 
       def foreign_key_name(table_name, options) # :nodoc:
         options.fetch(:name) do
-          identifier = "#{table_name}_#{options.fetch(:column)}_fk"
-          if identifier.length > allowed_index_name_length
-            raise ArgumentError, "Foreign key name '#{identifier}' is too long; the limit is #{allowed_index_name_length} characters"
-          end
-          identifier
+          "fk_rails_#{SecureRandom.hex(5)}"
         end
       end
 
diff --git a/activerecord/lib/active_record/schema_dumper.rb b/activerecord/lib/active_record/schema_dumper.rb
index 84ce725409..64bc68eefd 100644
--- a/activerecord/lib/active_record/schema_dumper.rb
+++ b/activerecord/lib/active_record/schema_dumper.rb
@@ -226,10 +226,20 @@ HEADER
             parts = [
                      'add_foreign_key ' + remove_prefix_and_suffix(foreign_key.from_table).inspect,
                      remove_prefix_and_suffix(foreign_key.to_table).inspect,
-                     'column: ' + foreign_key.column.inspect,
-                     'primary_key: ' + foreign_key.primary_key.inspect,
-                     'name: ' + foreign_key.name.inspect
                     ]
+
+            if foreign_key.column != @connection.foreign_key_column_for(foreign_key.to_table)
+              parts << ('column: ' + foreign_key.column.inspect)
+            end
+
+            if foreign_key.custom_primary_key?
+              parts << ('primary_key: ' + foreign_key.primary_key.inspect)
+            end
+
+            if foreign_key.name !~ /^fk_rails_[0-9a-f]{10}$/
+              parts << ('name: ' + foreign_key.name.inspect)
+            end
+
             parts << ('on_update: ' + foreign_key.on_update.inspect) if foreign_key.on_update
             parts << ('on_delete: ' + foreign_key.on_delete.inspect) if foreign_key.on_delete