These two tables are, like the mailouts table, wrapped by a PHP class, this time called ProcessingItems.

与mailout s表一样，这两个表也由php类包装，这个类称为ProcessingItems。

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The disadvantages are that every time a new attribute is added anywhere in the class hierarchy a new attribute must be added to the table.

缺点是每次在类层次结构的任何地方添加一个新属性时都必须将一个新属性添加到表中。

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The current strategy for maximizing performance and convenience is to retrieve metadata for a particular table the first time an instance of the class that maps to that table is instantiated.

为了使性能最大化和更加便利，目前的策略是从某一个表中提出元数据，先把一个类的实例映射到那个表上，用来初始化。

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With the boom in global demand for alternative-fueled vehicles, now may be a good time to break out your Periodic Table of Elements from science class.

FORBES: Chile Gets A Charge From Lithium