在创建映射时，必须为枚举的键传入这个类。

When you create the map, you must pass in the class for the enumerated key.

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这是映射(map)的一个绝好用例，在这里，每个映射(map)的键都是一个枚举值，而每个值都是键的错误信息。

This is a great use-case for a Map, in which each key of the Map is one of these enumerated values, and each value is the error message for that key. Listing 10 illustrates how this works.

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演示如何使用布尔值、外键和枚举列类型来执行表行筛选。

Shows how to perform table-row filtering using Boolean, foreign-key, and enumeration column types.

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