默认情况下，该类为空，因为Rails将根据来自数据库的表元数据推断该类的属性。

The class is empty by default, as Rails infers the attributes of the class based on table metadata from the database.

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通过属性表定义元数据。

Define the metadata through property sheets.

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创建“现有表”时，首先会创建一个代理表，然后检索和存储远程表中的元数据，并将该元数据放入到这个代理表中。

Creating an "existing table" creates a proxy table, then retrieves and stores metadata from a remote table and places the metadata into the proxy table.

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