No INNER JOIN on get rank in simple cases.

This eliminates the subquery and improves the performance a lot.

From Casecommons#332

lib/pg_search/scope_options.rb

@@ -14,13 +14,12 @@ def initialize(config)
 
  def apply(scope)
  scope = include_table_aliasing_for_rank(scope)
- rank_table_alias = scope.pg_search_rank_table_alias(include_counter: true)
 
- scope
- .joins(rank_join(rank_table_alias))
-  .order(Arel.sql("#{rank_table_alias}.rank DESC, #{order_within_rank}"))
- .extend(WithPgSearchRank)
-  .extend(WithPgSearchHighlight[feature_for(:tsearch)])
+ if config.associations.any?
+ apply_with_inner_join(scope)
+ else
+ apply_without_inner_join(scope)
+ end
  end
 
  module WithPgSearchHighlight
@@ -54,6 +53,34 @@ def with_pg_search_rank
  end
  end
 
+ module WithPgSearchRankNoInnerJoin
+ def self.[](rank_value)
+ Module.new do
+ include WithPgSearchRankNoInnerJoin
+ define_method(:rank_value) { rank_value }
+ end
+ end
+
+ def rank_field
+ "#{rank_value} AS pg_search_rank"
+ end
+
+ def rank_value
+ raise TypeError, "You need to instantiate this module with []"
+ end
+
+ def with_pg_search_rank
+ scope = self
+ scope = scope.select("#{table_name}.*") unless scope.select_values.any?
+ scope.select(rank_field)
+ end
+
+ def where_pg_search_rank(value)
+ scope = self
+ scope.where("#{rank_value}#{value}")
+ end
+ end
+
  module PgSearchRankTableAliasing
  def pg_search_rank_table_alias(include_counter: false)
  components = [arel_table.name]
@@ -78,6 +105,24 @@ def increment_counter
 
  delegate :connection, :quoted_table_name, to: :model
 
+ def apply_with_inner_join(scope)
+ rank_table_alias = scope.pg_search_rank_table_alias(include_counter: true)
+
+ scope
+ .joins(rank_join(rank_table_alias))
+ .order(Arel.sql("#{rank_table_alias}.rank DESC, #{order_within_rank}"))
+ .extend(WithPgSearchRank)
+ .extend(WithPgSearchHighlight[feature_for(:tsearch)])
+ end
+
+ def apply_without_inner_join(scope)
+ scope
+ .where(conditions)
+ .order(Arel.sql("#{rank_order}, #{order_within_rank}"))
+ .extend(WithPgSearchRankNoInnerJoin[rank])
+ .extend(WithPgSearchHighlight[feature_for(:tsearch)])
+ end
+
  def subquery
  model
  .unscoped
@@ -94,6 +139,7 @@ def conditions
  .reject { |_feature_name, feature_options| feature_options && feature_options[:sort_only] }
  .map { |feature_name, _feature_options| feature_for(feature_name).conditions }
  .inject { |accumulator, expression| Arel::Nodes::Or.new(accumulator, expression) }
+ .to_sql
  end
 
  def order_within_rank
@@ -145,6 +191,10 @@ def rank_join(rank_table_alias)
  "INNER JOIN (#{subquery.to_sql}) AS #{rank_table_alias} ON #{primary_key} = #{rank_table_alias}.pg_search_id"
  end
 
+ def rank_order
+ "#{rank} DESC"
+ end
+
  def include_table_aliasing_for_rank(scope)
  return scope if scope.included_modules.include?(PgSearchRankTableAliasing)
 

spec/integration/pg_search_spec.rb

@@ -345,7 +345,7 @@
  twice = ModelWithPgSearch.create!(content: 'foo foo')
 
  records = ModelWithPgSearch.search_content('foo')
- .where("#{PgSearch::Configuration.alias(ModelWithPgSearch.table_name)}.rank > 0.07")
+ .where_pg_search_rank(' > 0.07')
 
  expect(records).to eq [twice]
  end