How do I create linked X entities for a X entity using Entity Framework Core 2.0

Question

I want create a Product entity and that entity can have list of Products as LinkedProducts but I don't know why my codes not working. I'm student and very newbie to EF core mapping.
I created 2 Entity Classes Product.cs and ProductLink.cs, here is my classes

Product.cs

    public class Product : Content
    {
        public virtual string Description { get; set; }

        public virtual Guid? ThumbnailImageId { get; set; }

        [ForeignKey("ThumbnailImageId")]
        public virtual Media ThumbnailImage { get; set; }

        public virtual List<ProductLink> ProductLinks { get; set; } = new List<ProductLink>();
    }

ProductLink.cs

    public class ProductLink : EntityBase
    {
        [ForeignKey("ProductId")]
        public virtual Product Product { get; set; }

        public virtual Guid? ProductId { get; set; }

        [ForeignKey("LinkedProductId")]
        public virtual Product LinkedProduct { get; set; }

        public virtual Guid? LinkedProductId { get; set; }
    }

Error :

Unable to determine the relationship represented by navigation property 'Product.ProductLinks' of type 'List'. Either manually configure the relationship, or ignore this property using the '[NotMapped]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.

Answer 1

You have two relationships through ProductLink.Product and ProductLink.LinkedProduct reference navigation properties, but only one collection navigation property Product.ProductLinks, so EF does not know how to map them.

The minimum change required is to map the ProductLinks to one of the two related properties, for instance using InverseProperty attribute:

[InverseProperty("Product")]
public virtual List<ProductLink> ProductLinks { get; set; } = new List<ProductLink>();

For more info, see Relationships documentation topic.

Answer 2

So a bit more information on what exactly you're trying to do here would be helpful. From what I can see though, everything can probably be consolidated into a single Product class like so.

    public class Product : Content
    {
        public virtual string NormalizedName { get; set; }

        public virtual string ShortDescription { get; set; }

        public virtual string Description { get; set; }

        public virtual Guid? ThumbnailImageId { get; set; }

        [ForeignKey("ThumbnailImageId")]
        public virtual Media ThumbnailImage { get; set; }

        [ForeignKey("ProductId")]
        public virtual Guid? ProductId { get; set; }

        [ForeignKey("LinkId")]
        public virtual Guid? LinkId { get; set; }

        public virtual List<Product> ProductLinks { get; set; } = new List<Product>();
    }

What error are you receiving exactly?