From 9cdd0a1fdf8308985231242d378e3a1c29c4ab00 Mon Sep 17 00:00:00 2001 From: Derek Prior Date: Fri, 21 Feb 2014 11:33:36 -0500 Subject: Use type column first in multi-column indexes `add_reference` can very helpfully add a multi-column index when you use it to add a polymorphic reference. However, the first column in the index is the `id` column, which is less than ideal. The [PostgreSQL docs][1] say: > A multicolumn B-tree index can be used with query conditions that > involve any subset of the index's columns, but the index is most > efficient when there are constraints on the leading (leftmost) > columns. The [MySQL docs][2] say: > MySQL can use multiple-column indexes for queries that test all the > columns in the index, or queries that test just the first column, the > first two columns, the first three columns, and so on. If you specify > the columns in the right order in the index definition, a single > composite index can speed up several kinds of queries on the same > table. In a polymorphic relationship, the type column is much more likely to be useful as the first column in an index than the id column. That is, I'm more likely to query on type without an id than I am to query on id without a type. [1]: http://www.postgresql.org/docs/9.3/static/indexes-multicolumn.html [2]: http://dev.mysql.com/doc/refman/5.0/en/multiple-column-indexes.html --- .../active_record/connection_adapters/abstract/schema_definitions.rb | 2 +- .../lib/active_record/connection_adapters/abstract/schema_statements.rb | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) (limited to 'activerecord/lib') 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 adb9fcaeb8..7534fde03e 100644 --- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb +++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb @@ -312,7 +312,7 @@ module ActiveRecord args.each do |col| column("#{col}_id", type, options) column("#{col}_type", :string, polymorphic.is_a?(Hash) ? polymorphic : options) if polymorphic - index(polymorphic ? %w(id type).map { |t| "#{col}_#{t}" } : "#{col}_id", index_options.is_a?(Hash) ? index_options : {}) if index_options + index(polymorphic ? %w(type id).map { |t| "#{col}_#{t}" } : "#{col}_id", index_options.is_a?(Hash) ? index_options : {}) if index_options end end alias :belongs_to :references 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 7105df1ee4..cbf87df356 100644 --- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb +++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb @@ -629,7 +629,7 @@ module ActiveRecord type = options.delete(:type) || :integer add_column(table_name, "#{ref_name}_id", type, options) add_column(table_name, "#{ref_name}_type", :string, polymorphic.is_a?(Hash) ? polymorphic : options) if polymorphic - add_index(table_name, polymorphic ? %w[id type].map{ |t| "#{ref_name}_#{t}" } : "#{ref_name}_id", index_options.is_a?(Hash) ? index_options : {}) if index_options + add_index(table_name, polymorphic ? %w[type id].map{ |t| "#{ref_name}_#{t}" } : "#{ref_name}_id", index_options.is_a?(Hash) ? index_options : {}) if index_options end alias :add_belongs_to :add_reference -- cgit v1.2.3