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c#linqentity-frameworklambda
Pete
Pete

Reputation: 2463

Find top level entities in self referencing table

In Entity Framework, how do I search for objects that are at the top level in EF?

If I have a group of subassemblies that have subcomponents. Those subassemblies can be placed in larger assemblies.

In a real world example: Let's say we build a cabinet with a computer and the computer has parts. How do I find the computers that have not been installed in a cabinet or, perhaps, parts not installed in a computer?

public class Component
{
    public int Id { get; set; }
    public string Model { get; set; }
    public string PartId { get; set; }
    public DateTime Manufactured { get; set; }
    public string SerialNumber { get; set; }
    public string ProductType { get; set; }
    public string Description { get; set; }
    public virtual List<Component> SubComponents { get; set; }
}

Upvotes: 2

Views: 589

Answers (1)

Pete
Pete

Reputation: 2463

I think I found my answer here...Self Referencing Tables

public class Component
{
    [Key]
    public int Id { get; set; }
    public string Model { get; set; }
    public string PartId { get; set; }
    public DateTime Manufactured { get; set; }
    public string SerialNumber { get; set; }
    public string ProductType { get; set; }

    //Added this...
    public int? ParentComponentId { get; set; }
    [ForeignKey("ParentComponentId")]
    public virtual Component ParentComponent { get; set; }

    public virtual List<Component> SubComponents { get; set; }
    public string Description { get; set; }
}

Originally I was trying to add a Foreign Key to the SubComponents but I actually needed a FK on the parent relationship. Now my EF query looks like this...

return _db.Components.Where(x => x.ParentComponent == null).ToList();

Upvotes: 3

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