How to reduce request to my db?

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MVC3

i have a partial view with a gridview in it. so when user clicks add button request will redirect to Add method of unitsController and after add it to databse i should refetch all data from database! is there a way to prevent controller from get all database records? below is my current controller

public class UnitsController : Controller
{
    TList<Units> model=null;

    public ActionResult UnitsPartial()
    {
        if(model==null)
          model = database.GetAll();
        return PartialView(model);
    }

    [HttpPost]
    public ActionResult Add(Units unit)
    {
        if (ModelState.IsValid)
        {
            database.Save(unit);
            model.Add(unit);          
        }

        return PartialView("UnitsPartial", model);
    }

in the last line i want to use return PartialView("UnitsPartial", model) instead return database.GetAll() to prevent a databse query, but model is null in Add method!
is my approach correct or not? and why model is null in add method?