在实体框架中使用现有外键值

Question

I am using Entity Framework Code First. I have two model classes, Currency and Invoice:

public class Currency
{
    [HiddenInput(DisplayValue = false)]
    public int CurrencyID { get; set; }
    public string ShortName { get; set; }
    public string FullName { get; set; }

    [Required(ErrorMessage = "Please enter a positive price")]
    public double Rate { get; set; }
}

public class Invoice
{
    public int InvoiceID { get; set; }
    public int CurrencyID { get; set; }
    public double RateOfExchange { get; set; }
    public double CurrencyAmount { get; set; }

    public virtual Currency Currency { get; set; }
    public virtual Customer Customer { get; set; }
}

I have some initialized my database with some Currency values. Whenever I add a new Invoice, I want it to use existing values from the Currency table for its Currency property but every time I create a new Invoice value and assign its Currency property with an existing value from the Currency table, it creates a duplicate value in the currency table. How can I solve this problem.

Answer 1

Above the line:

public virtual Currency Currency { get; set;}

Add the following attribute:

[ForeignKey("CurrencyID")]