For qualifying blogs, this is an alternate source of revenue.
对于高质量的博客，这是一个替代的收入来源。
This may be the best policy when the alternate source provides no IDs.
当备用源不提供ID时，这可能是最好的策略。
Understand whether an alternate source provides valid IDs or no IDs.
了解备用源是否提供有效的ID或者不提供ID。
The real alternate source may provide valid IDs, invalid IDs, or no IDs.
实际的备用源可能提供有效的ID、无效的ID、或者不提供ID。
To cache the records from the alternate source, you need a cache per value type returned.
要缓存这些来自备用源的记录，您需要为返回的每种值类型设置一个缓存。
This means that an alternate source used by the facade must return either valid IDs or no IDs.
这意味着，facade所使用的备用源必须返回有效的ID或者不返回ID。
If you lost your main source of income tomorrow, could you find an alternate source to replace it?
如果你明天失去了主要的经济来源，你能找到一个取代它的供选择的来源吗？
You can determine which subpolicy to use (the first or the second) by knowing whether or not the alternate source returns valid IDs.
通过了解备用源是否返回有效的 ID，您可以确定使用哪个子策略（第一个还是第二个）。
This policy may be most useful in migration scenarios when coupled with some sort of clean-up mechanism associated with the alternate source.
在迁移场景中，当与关联于备用源的某些类型的清理机制结合使用时，这个策略可能是最有价值的。
If an alternate source doesn't natively expose the same interface, you can apply a transform pattern to the source; however, this pattern is out of this article's scope.
如果一个备用源没有在本地公开相同的接口，那么您可以对这个源应用转换模式，然而对这个模式的讨论超出了本文的范围。
The mechanism (out of scope for this pattern) would run periodically to remove entity records that shouldn't be migrated from an alternate source to the preferred source.
这种机制（超出了这个模式范围）将周期性地运行，以删除那些不应该从备用源迁移到首选源的实体记录。
You may require a different set of actions when the matching records from an alternate source don't have a valid ID or have no ID; this would be the case for external sources like Acxiom.
当来自备用源的匹配记录不包含有效的ID或者没有 ID时，您可能需要进行一组不同的操作，对于外部源，如 Acxiom，便是这种情况。
You may require a different set of actions when the matching records from an alternate source don't have a valid ID or have no ID; this would be the case for external sources like Acxiom.
当来自备用源的匹配记录不包含有效的ID或者没有 ID时，您可能需要进行一组不同的操作，对于外部源，如 Acxiom，便是这种情况。
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