在Entity Framework中将两个外键定义为主键

Question

In Entity Framework, I'd like to use two foreign keys as primary key of another entity type.

public class CustomerExtensionValue {

    // Values for extended attributes of a customer
    [Key]
    [Column(Order = 0)]
    public Customer Customer { get; set; }

    [Key]
    [Column(Order = 1)]
    public CustomerExtension Extension { get; set; }

    [Required]
    public string Value { get; set; }
}

However, this gives me an error that a key would be missing. \\tSystem.Data.Entity.Edm.EdmEntityType: : EntityType 'CustomerExtensionValue' has no key defined. Define the key for this EntityType.

I'm know I could define two more attributes holding the primary keys of the referenced entity types. Is Visual Studio not smart enough to use their primary keys on his own?

Answer 1

Primary keys always must be defined by scalar properties in the entity class. You cannot refer to the PKs by navigation properties alone. In your model a definition like this is required:

public class CustomerExtensionValue {

    [Key, ForeignKey("Customer"), Column(Order = 0)]
    public int CustomerId { get; set; }

    [Key, ForeignKey("Extension"), Column(Order = 1)]
    public int ExtensionId { get; set; }

    public Customer Customer { get; set; }
    public CustomerExtension Extension { get; set; }

    [Required]
    public string Value { get; set; }
}