From 80f16946bb89ef37f5ee0cb6c4a4c643424521a6 Mon Sep 17 00:00:00 2001
From: Jon Leighton <j@jonathanleighton.com>
Date: Fri, 18 May 2012 20:48:11 +0100
Subject: Perf: Don't load the association for #delete_all.

Bug #6289
---
 .../active_record/associations/collection_association.rb | 14 ++++++++++++--
 .../associations/has_and_belongs_to_many_association.rb  | 16 +++++++++++-----
 .../active_record/associations/has_many_association.rb   |  8 ++++++--
 .../associations/has_many_through_association.rb         |  7 ++++++-
 4 files changed, 35 insertions(+), 10 deletions(-)

(limited to 'activerecord/lib')

diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index 3af5ff3eab..99a32028a3 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -146,7 +146,7 @@ module ActiveRecord
       #
       # See delete for more info.
       def delete_all
-        delete(load_target).tap do
+        delete(:all).tap do
           reset
           loaded!
         end
@@ -218,7 +218,17 @@ module ActiveRecord
       # are actually removed from the database, that depends precisely on
       # +delete_records+. They are in any case removed from the collection.
       def delete(*records)
-        delete_or_destroy(records, options[:dependent])
+        dependent = options[:dependent]
+
+        if records.first == :all
+          if loaded? || dependent == :destroy
+            delete_or_destroy(load_target, dependent)
+          else
+            delete_records(:all, dependent)
+          end
+        else
+          delete_or_destroy(records, dependent)
+        end
       end
 
       # Destroy +records+ and remove them from this association calling
diff --git a/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb b/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb
index a4cea99372..e8ae3e51b9 100644
--- a/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb
+++ b/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb
@@ -46,11 +46,17 @@ module ActiveRecord
           if sql = options[:delete_sql]
             records.each { |record| owner.connection.delete(interpolate(sql, record)) }
           else
-            relation = join_table
-            stmt = relation.where(relation[reflection.foreign_key].eq(owner.id).
-              and(relation[reflection.association_foreign_key].in(records.map { |x| x.id }.compact))
-            ).compile_delete
-            owner.connection.delete stmt
+            relation  = join_table
+            condition = relation[reflection.foreign_key].eq(owner.id)
+
+            unless records == :all
+              condition = condition.and(
+                relation[reflection.association_foreign_key]
+                  .in(records.map { |x| x.id }.compact)
+              )
+            end
+
+            owner.connection.delete(relation.where(condition).compile_delete)
           end
         end
 
diff --git a/activerecord/lib/active_record/associations/has_many_association.rb b/activerecord/lib/active_record/associations/has_many_association.rb
index 059e6c77bc..e631579087 100644
--- a/activerecord/lib/active_record/associations/has_many_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_association.rb
@@ -89,8 +89,12 @@ module ActiveRecord
             records.each { |r| r.destroy }
             update_counter(-records.length) unless inverse_updates_counter_cache?
           else
-            keys  = records.map { |r| r[reflection.association_primary_key] }
-            scope = scoped.where(reflection.association_primary_key => keys)
+            if records == :all
+              scope = scoped
+            else
+              keys  = records.map { |r| r[reflection.association_primary_key] }
+              scope = scoped.where(reflection.association_primary_key => keys)
+            end
 
             if method == :delete_all
               update_counter(-scope.delete_all)
diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index 53d49fef2e..65a48a5e00 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -126,7 +126,12 @@ module ActiveRecord
         def delete_records(records, method)
           ensure_not_nested
 
-          scope = through_association.scoped.where(construct_join_attributes(*records))
+          # This is unoptimised; it will load all the target records
+          # even when we just want to delete everything.
+          records = load_target if records == :all
+
+          scope = through_association.scoped
+          scope.where! construct_join_attributes(*records)
 
           case method
           when :destroy
-- 
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