Decrease in a field of table Asp.net MVC

Question

I am developing course manager in Asp.net MVC, and in the course table has a field qty vacancies. I wonder how I do to make one Count-- (or some other way to Decrease) this field. For example: In the list of courses will appear the courses and the amount of vacancies and a sign up button. The student by clicking sign up, the field qty vacancies decreasing the number of vacancies in the table and on screen. Courses with 50 vacancies, if an application is made will decrease 49, 48, 47... How I make the field automatically update both table and user screen!?

Answer 1

I’m guessing you’re using Entity Framework to abstract the database. An example of Action in the Controller it would be something like that:

public ActionResult Inscrever(int id) // Este id é o id do curso
{
    // Aqui penso que ocorreria uma seleção do aluno logado.
    // Depois uma associação do aluno ao curso.
    // Suponho que o curso seria colocado em uma variável "curso".
    curso.QuantidadeVagas--;
    context.Entry(curso).State = EntityState.Modified;
    context.SaveChanges();
    return RedirectToAction("AlgumaAction", "AlgumController");
}

Only that as are various bank operations you do here (select student, select course, create association, modify course), recommend you use transactional scope. Then I’d be like this:

public ActionResult Inscrever(int id) 
{
    using (var scope = new TransactionScope()) 
    {
        // Aqui penso que ocorreria uma seleção do aluno logado.
        // Depois uma associação do aluno ao curso.
        // Suponho que o curso seria colocado em uma variável "curso".
        curso.QuantidadeVagas--;
        context.Entry(curso).State = EntityState.Modified;
        context.SaveChanges();

        scope.Complete(); 
    }

    return RedirectToAction("AlgumaAction", "AlgumController");
}

For display on screen, it is trivial: the course value update will automatically reflect on the presentation:

@model Curso

<h1>Quantidade de Vagas: @Model.QuantidadeVagas</h1>

---

An example of Ajax would be a button like this:

<button id="decremento" name="1">Decrementar</button>

Add jQuery to your Views (try to use Bundling) and write something like that:

<script>
    $(document).ready(function() {
        $("#decremento").click(function() {
            $.ajax({
              type: "POST",
              url: '/MeuController/Inscrever/' + $(this).attr("name")
            });
        });
    }); 
</script>