fixed association preloading to use = instead of IN when there's only one record

[#1013 state:committed]
Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

activerecord/lib/active_record/association_preload.rb

@@ -95,7 +95,7 @@ def preload_has_and_belongs_to_many_association(records, reflection, preload_opt
         records.each {|record| record.send(reflection.name).loaded}
         options = reflection.options
 
-        conditions = "t0.#{reflection.primary_key_name}  IN (?)"
+        conditions = "t0.#{reflection.primary_key_name} #{in_or_equals_for_ids(ids)}"
         conditions << append_conditions(options, preload_options)
 
         associated_records = reflection.klass.find(:all, :conditions => [conditions, ids],
@@ -222,8 +222,6 @@ def preload_belongs_to_association(records, reflection, preload_options={})
 
           table_name = klass.quoted_table_name
           primary_key = klass.primary_key
-          conditions = "#{table_name}.#{connection.quote_column_name(primary_key)} IN (?)"
-          conditions << append_conditions(options, preload_options)
           column_type = klass.columns.detect{|c| c.name == primary_key}.type
           ids = id_map.keys.uniq.map do |id|
             if column_type == :integer
@@ -234,6 +232,8 @@ def preload_belongs_to_association(records, reflection, preload_options={})
               id
             end
           end
+          conditions = "#{table_name}.#{connection.quote_column_name(primary_key)} #{in_or_equals_for_ids(ids)}"
+          conditions << append_conditions(options, preload_options)
           associated_records = klass.find(:all, :conditions => [conditions, ids],
                                           :include => options[:include],
                                           :select => options[:select],
@@ -248,10 +248,10 @@ def find_associated_records(ids, reflection, preload_options)
         table_name = reflection.klass.quoted_table_name
 
         if interface = reflection.options[:as]
-          conditions = "#{reflection.klass.quoted_table_name}.#{connection.quote_column_name "#{interface}_id"} IN (?) and #{reflection.klass.quoted_table_name}.#{connection.quote_column_name "#{interface}_type"} = '#{self.base_class.sti_name}'"
+          conditions = "#{reflection.klass.quoted_table_name}.#{connection.quote_column_name "#{interface}_id"} #{in_or_equals_for_ids(ids)} and #{reflection.klass.quoted_table_name}.#{connection.quote_column_name "#{interface}_type"} = '#{self.base_class.sti_name}'"
         else
           foreign_key = reflection.primary_key_name
-          conditions = "#{reflection.klass.quoted_table_name}.#{foreign_key} IN (?)"
+          conditions = "#{reflection.klass.quoted_table_name}.#{foreign_key} #{in_or_equals_for_ids(ids)}"
         end
 
         conditions << append_conditions(options, preload_options)
@@ -277,6 +277,9 @@ def append_conditions(options, preload_options)
         sql
       end
 
+      def in_or_equals_for_ids(ids)
+        ids.size > 1 ? "IN (?)" : "= ?"
+      end
     end
   end
 end

activerecord/test/cases/inheritance_test.rb

@@ -193,7 +193,7 @@ def test_eager_load_belongs_to_something_inherited
 
   def test_eager_load_belongs_to_primary_key_quoting
     con = Account.connection
-    assert_sql(/\(#{con.quote_table_name('companies')}.#{con.quote_column_name('id')} IN \(1\)\)/) do
+    assert_sql(/\(#{con.quote_table_name('companies')}.#{con.quote_column_name('id')} = 1\)/) do
       Account.find(1, :include => :firm)
     end
   end