CODEWITHSUNDEEP
c#asp.net-mvcentity-frameworkinheritancemany-to-many
Matthew Hudson
Matthew Hudson

Reputation: 1316

MVC - How to best implement Many-To-Many relationship to TPT Derived Entity (DB First) in DB and EDMX

This week I've been experimenting with inheritance, something which until recently I hadn't used much.

In simplest terms: I need to implement a sign up system for Vendors, who once verified are able to purchase multiple packages. Rather than simply creating a Vendors class, I wanted to try out Table-Per-Type inheritance from a Person entity. Originally I had the below implementation.

Implementation 1

This implementation worked as far as creating a PersonLogin and verifying the account. However as soon as I tried to use the PersonLogin as a Vendor I realized I was stuck as each Person must be of a specific sub-type and cannot be multiple.

So back to the drawing board I went: I redesigned my DB to have Vendors inherit from the PersonLogin entity, and the PersonLogin to inherit from the Person entity.

implementation 2

I am now implementing this second version, however as I'm relatively new to the world of inheritance I am not sure whether I have done it correctly or efficiently.

I want to find the best way to accomplish this functionality, whether I use inheritance or relationships is irrelevant.

Current Controller Action for adding Packages to Vendors:

[HttpPost]
public ActionResult RegisterPackage(int packageID, int personID)
{
    if (ModelState.IsValid)
    {
        db.PackagesInVendors.Add(new PackagesInVendor() { PackageID = packageID, VendorID = personID });
        db.SaveChanges();
        return View("Index");
    }
    ViewBag.Packages = new SelectList(db.Packages, "ID", "Name", packageID);
    ViewBag.People = new SelectList(db.People, "PersonID", "Email", personID);
    return View();
}

All feedback or suggestions are most welcome, Cheers.

Upvotes: 0

Views: 136

Answers (1)

Neil Thompson
Neil Thompson

Reputation: 6425

Good question and good investigation.

I'm keen to see what others post, but I 'save' TPT Inheritance for special cases where it would be more work to avoid database inheritance than to use it.

In your Vendor-Person scenario I would use composition over inheritance and include a ForeignKey Vendor.PersonId

I wouldn't use inheritance at all in your scenario.

An example where I might use inheritance would be if I had 'base type' Product that had 'categories' with their own properties, ie: ClothingProduct, ToyProduct, ExperienceProduct etc.

One gotcha of EF TPT inheritance is that it's easy to work with inherited tables in EF - but in one situation satellite websites were also using the raw data with sql queries and I am told it made data access for them much harder.

Upvotes: 1

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