Tukukkk

I have designed the domain models for my ASP.NET Core server side application with join tables to create many-to-many relationships. I am unsure if the design is sound and I am trying to understand if there are common design patterns for my model. I am inexperienced in designing models. I have included an abstraction of my models below.

My business rules are: an Owner can own many PencilCase. PencilCase is in the theme of ColorsInCase and a Color can only exist once in the PencilCase, but the PencilCase can have a collection of Pen (in different Size) in that Color and a collection of Pencil in that Color (again in different Size). The PencilCase should not hold two Pen of the same Size in the same Color (same for Pencil).

An example of where I am doubtful for my design: ColorInCase has its own Id while it could be a composite of PencilCaseId and ColorId. But then I am not sure how I can reference ColorInCase in Pen and Pencil if it doesn't have its own Id.

Another example of my concern: my principal object is actually the Owner, but in this design I would start from PencilCase to get a relationship with Owner. I am not sure if this will get me in difficulty later on.

Is this a sound model design, or is there a common design pattern for these nested many-to-many relationships (or nested collections)?

public class Owner

{

    public int Id { get; set; }

    public string Name { get; set; }

}

public class PencilCase

{

    public int Id { get; set; }

    public int OwnerId { get; set; }

    public Owner Owner { get; set; }

    public List<ColorInCase> ColorsInCase { get; set; }

    public PencilCase()

    {

        ColorsInCase = new List<ColorInCase>();

    }



}

public class Color

{

    public int Id { get; set; }

    public string Name { get; set; }

}

public class ColorInCase

{

    public int Id { get; set; }

    public int PencilCaseId { get; set; }

    public PencilCase PencilCase { get; set; }

    public int ColorId { get; set; }

    public Color Color { get; set; }

    public List<Pencil> Pencils { get; set; }

    public List<Pen> Pens { get; set; }

    public ColorInCase()

    {

        Pencils = new List<Pencil>();

        Pens = new List<Pen>();

    }

}



public class Pen

{

    public byte Size { get; set; }

    public int ColorInCaseId { get; set; }

    public ColorInCase ColorInCase { get; set; }



}



public class Pencil

{

    public byte Size { get; set; }

    public int ColorInCaseId { get; set; }

    public ColorInCase ColorInCase { get; set; }

}

Pen and Pencil have a key created by ModelBuilder on Size and