Add an attribute called id of type Key (see the import list for the fully qualified class name).

添加一个类型为Key的id属性(见于完全合格类名的导入列表)。

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An Entity class needs a primary key.

Entity类需要一个主键。

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You can also create a primary key class for entities that have composite keys.

还可以为具有组合键的实体创建一个主键类。

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Urban boosters, apartment-builders and greens--all advocates of expanding the renter class--tend to ignore several key facts.

FORBES: New Geographer

Watkins wanted to turn the school's sports into a big-time Division One program and thought that building a first-class stadium was the key.

FORBES: Show Me the Money

But Gore's stridency and class warfare rhetoric were off-key.

FORBES: Election Stranger Than Fiction