代码详解—本部分详细解释源代码各部分如何相互配合，以便您可以针对其他类型的元数据和源轻松扩展它。

Code walkthrough-review the code with an explanation of how it all fits together so you can easily extend it for other types of metadata and sources.

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框架查询两个元数据源：活动记录模型和每个模型对象的定制元数据文件。

The framework queries two sources of metadata: the Active Record model and a custom metadata file for each model object.

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然后该信息用于优化内存使用率和内部表示该用户的数据源元数据的安全视图。

This information is then used to optimize the memory usage and internal representation of that user's secured view of the data source metadata.

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