Usually media failure is caused by either the complete loss of a data file or a system change number (SCN) time stamp being out of sync with the rest of the database.
In this case, mocking out the database interaction allows you to focus on the Grails functionality, doing it in a fraction of the time it would otherwise take.
在这种情况下，模拟数据库交互可以使您专注于Grails功能，只花少部分时间来进行测试。
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Retrieving a single Person out of the database could very well lead to retrieving all of humanity back to the beginning of time.