String in Unique Key in Entity Framework

Is it possible to put a string in Unique Key ?

    public int ID{ get; set; }

    public string TweetID { get; set; }

Because I need ID in primary key (it's ok) and TweetID in unique key (for no duplication in database)

EDI开发者_如何学运维T : I use Entity Framework 4 and MVC3

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It is possible to define unique key on string column but you must do it in the database (as unique index) because none of current EF versions support unique keys.