How to check if a record already exists in the db using asp.Net MVC

Question

I'm trying in asp.net MVC to see if a customer has already got an agreement associated to them. This is so the customer can only have 1 agreement assigned to them. I have looked at various examples Best way to check if object exists in Entity Framework? and http://www.experts-exchange.com/questions/28371483/MVC-Controller-Check-If-A-Record-Exists-Before-inserting-Call-a-method.html but can't seem to get them working in my solution. I would like to have it in the Create Action method.

This is my Create controller

     public ActionResult Create()
    {
        ViewBag.CustomerId = new SelectList(db.Customers, "CustomerID", "LastName");
        ViewBag.SupplierId = new SelectList(db.Suppliers, "SupplierId", "SupplierName");
        return View();
    }

    // POST: Agreements/Create
    // To protect from overposting attacks, please enable the specific properties you want to bind to, for 
    // more details see http://go.microsoft.com/fwlink/?LinkId=317598.
    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create([Bind(Include = "AgreementId,CustomerId,SupplierId")] Agreement agreement)
    {
        //Trying to check here before the create 
        /*
        var exists = (from c in db.Agreements
                   where c.CustomerId == C)
        */

        if (ModelState.IsValid)
        {
            agreement.AgreementId = Guid.NewGuid();
            db.Agreements.Add(agreement);
            db.SaveChanges();
            return RedirectToAction("Index");
        }

        ViewBag.CustomerId = new SelectList(db.Customers, "CustomerID", "LastName", agreement.CustomerId);
        ViewBag.SupplierId = new SelectList(db.Suppliers, "SupplierId", "SupplierName", agreement.SupplierId);
        return View(agreement);
    }

Can it be done this way?

Many thanks

Answer 1

db.Agreements.Any(ag=> ag.CustomerId == c)

Answer 2

Method 'FirstOrDefault' return null if not found that item.

var foo = db.FooTable.FirstOrDefault(w => w.Id == Id); if (foo == null) { }