如何在带有数据注释的实体框架中检索外键关系中的列子集

Question

Suppose I have an ordinary foreign-key column like this:

[Table("Thing")]
public class Thing
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid? Id { get; set; }

    public Guid? StatusId { get; set; }

    // want to omit this potentially large object
    [ForeignKey("StatusId")]
    public ThingStatus Status { get; set; } 

    // This column isn't in the Thing table; how to best populate it from ThingStatus?
    public string StatusName { get; set; }
    ...
}


[Table("ThingStatus")]
public class ThingStatus {...}

Now let us suppose ThingStatus has lots of columns, more than I want. Is there a slick way to retrieve only some of the values via the model annotations ? Instead of having a navigation property to ThingStatus, is there a way to tell EF to retrieve only ThingStatus.Name for my property StatusName, for example?

Assuming there's not, is there a more elegant way to get this than retrieving from ThingStatus via .Select and mapping it in code?

Answer 1

You can accomplish the desired effect by selecting an object. EF will only return what you tell it to select.

var results = myContext.Things
    .Select(x => new ThingViewModel()
    {
        StatusName = x.ThingStatus.Name
    })
    .ToList();