实体框架IsUnique并接受Null

Question

How can I make a Code First property that accepts null values but it's also an [Index(IsUnique=true)] ?

For example: a passport number should't be repeated, ergo the IsUnique , but if the user doesn't insert one, then it defaults to null, so it accepts multiple nulls.

Answer 1

Since it will not be unique then, you cannot do it that way. But you can manage it, by attaching a table:

public class Person {
    public int Id { get; set; }
}

public class Passport {
    [Key]
    public int PersonId { get; set; }
    [ForeignKey("PersonId")]
    public Person Person { get; set; }
    [Index(IsUnique=true)]
    public string PassportId { get; set; }
}

Be aware, that there are countries, which do not allow storing such numbers.