实体框架6：使用空或空白外键加载相关实体

Question

Parent has a collection of Child. Child has a Foreign Key to Parent (ParentID), but that foreign key might by null / blank. I want Entity Framework to always load Child with null / blank foreign key for all Parent.

public class Parent
{
    public string ID { get; set; }
    public virtual ICollection<Child> Children { get; set; } //Should load it's children AND children without foreign key.
}

public class Child
{
    public string ID { get; set; }
    public string ParentID { get; set; } //This can be null / blank.
}

Answer 1

Without a ParentId, the child is what's known as an orphan . There's no way to link a child to a parent without a populated foreign key property.

If you're just looking to query the Children for records with a null or empty ParentId, do something like the following with your DbContext:

var orphans = myContext.Children.Where(child => String.IsNullOrEmpty(child.ParentId));