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rd);      List<OrderItem> selectByExample(OrderItemExample example);      OrderItem selectByPrimaryKey(Integer id);      int updateByPrimaryKeySelective(OrderItem record);      int updateByPrimaryKey(OrderItem record); } 

This is the interface of the OrderItemMapper, which is responsible for CRUD operations on the order_item table in the database. It includes methods such as deleteByPrimaryKey, insert, selectByExample, and updateByPrimaryKey. These methods are used to manipulate data in the order_item table based on different conditions or parameters. For example, deleteByPrimaryKey method deletes a row from the table based on its primary key value; insert method inserts a new row into the table with values specified in an OrderItem object; selectByExample method retrieves rows from the table that match certain criteria specified by an OrderItemExample object; and so on.