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@@ -149,6 +149,10 @@ module ActiveRecord
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         "INSERT INTO #{quote_table_name(table_name)} VALUES(DEFAULT)"
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       end
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+      def case_sensitive_equality_operator
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+        "="
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+      end
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+
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       protected
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         # Returns an array of record hashes with the column names as keys and
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         # column values as values.

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@@ -511,6 +511,10 @@ module ActiveRecord
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         keys.length == 1 ? [keys.first, nil] : nil
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       end
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+      def case_sensitive_equality_operator
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+        "= BINARY"
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+      end
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+
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       private
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         def connect
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           @connection.reconnect = true if @connection.respond_to?(:reconnect=)

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@@ -627,17 +627,23 @@ module ActiveRecord
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           is_text_column = finder_class.columns_hash[attr_name.to_s].text?
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-          if !value.nil? && is_text_column
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-            value = value.to_s
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+          if value.nil?
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+            comparison_operator = "IS ?"
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+          else
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+            comparison_operator = "#{connection.case_sensitive_equality_operator} ?"
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+
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+            if is_text_column
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+              value = value.to_s
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+            end
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           end
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+          sql_attribute = "#{record.class.quoted_table_name}.#{connection.quote_column_name(attr_name)}"
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+
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           if value.nil? || (configuration[:case_sensitive] || !is_text_column)
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-            condition_sql = "#{record.class.quoted_table_name}.#{attr_name} #{attribute_condition(value)}"
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+            condition_sql = "#{sql_attribute} #{comparison_operator}"
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             condition_params = [value]
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           else
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-            # sqlite has case sensitive SELECT query, while MySQL/Postgresql don't.
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-            # Hence, this is needed only for sqlite.
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-            condition_sql = "LOWER(#{record.class.quoted_table_name}.#{attr_name}) #{attribute_condition(value)}"
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+            condition_sql = "LOWER(#{sql_attribute}) #{comparison_operator}"
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             condition_params = [value.downcase]
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           end
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@@ -654,28 +660,10 @@ module ActiveRecord
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             condition_params << record.send(:id)
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           end
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-          results = finder_class.with_exclusive_scope do
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-            connection.select_all(
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-              construct_finder_sql(
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-                :select     => "#{connection.quote_column_name(attr_name)}",
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-                :from       => "#{finder_class.quoted_table_name}",
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-                :conditions => [condition_sql, *condition_params]
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-              )
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-            )
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-          end
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-
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-          unless results.length.zero?
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-            found = true
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-
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-            # As MySQL/Postgres don't have case sensitive SELECT queries, we try to find duplicate
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-            # column in ruby when case sensitive option
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-            if configuration[:case_sensitive] && finder_class.columns_hash[attr_name.to_s].text?
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-              found = results.any? { |a| a[attr_name.to_s] == value.to_s }
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-            end
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-            
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-            if found
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+          finder_class.with_exclusive_scope do
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+            if finder_class.exists?([condition_sql, *condition_params])
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               message = record.errors.generate_message(attr_name, :taken, :default => configuration[:message])
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-              record.errors.add(attr_name, message) 
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+              record.errors.add(attr_name, message)
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             end
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           end
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         end