asp.net-mvc
Operación CRUD

Introducción

Observaciones

Crear - Parte del controlador

Para implementar la funcionalidad de crear necesitamos dos acciones: GET y POST .

1. La acción GET utilizada para devolver la vista muestra un formulario que permite al usuario ingresar datos usando elementos HTML. Si hay algunos valores predeterminados que deben insertarse antes de que el usuario agregue datos, debe asignarse a las propiedades del modelo de vista en esta acción.

2. Cuando el usuario complete el formulario y haga clic en el botón "Guardar", trataremos los datos del formulario. Por eso ahora necesitamos la acción POST . Este método será responsable de administrar los datos y guardarlos en la base de datos. En caso de cualquier error, la misma vista devuelta con datos de formulario almacenados y mensaje de error explica qué problema ocurre después de enviar la acción.

Implementaremos estos dos pasos dentro de dos métodos Create () dentro de nuestra clase de controlador.

    // GET: Student/Create 
    // When the user access this the link ~/Student/Create a get request is made to controller Student and action Create, as the page just need to build a blank form, any information is needed to be passed to view builder
    public ActionResult Create()
    {
        // Creates a ViewResult object that renders a view to the response.
        // no parameters means: view = default in this case Create and model = null
        return View();
    }

    // POST: Student/Create        
    [HttpPost]
    // Used to protect from overposting attacks, see http://stackoverflow.com/documentation/asp.net-mvc/1997/html-antiforgerytoke for details
    [ValidateAntiForgeryToken]
    // This is the post request with forms data that will be bind the action, if in the data post request have enough information to build a Student instance that will be bind
    public ActionResult Create(Student student)
    {
        try
        {
        //Gets a value that indicates whether this instance received from the view is valid.
            if (ModelState.IsValid)
            {
                // Adds to the context
                db.Students.Add(student);
                // Persist the data 
                db.SaveChanges();
                // Returns an HTTP 302 response to the browser, which causes the browser to make a GET request to the specified action, in this case the index action.
                return RedirectToAction("Index");
            }
        }
        catch 
        {
            // Log the error (uncomment dex variable name and add a line here to write a log).
            ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists see your system administrator.");
        }
        // view = default in this case Create and model = student
        return View(student);
    }

Crear - Ver parte

@model ContosoUniversity.Models.Student

//The Html.BeginForm helper Writes an opening <form> tag to the response. When the user submits the form, the request will be processed by an action method.                 
@using (Html.BeginForm()) 
{
    //Generates a hidden form field (anti-forgery token) that is validated when the form is submitted.
    @Html.AntiForgeryToken()
    
<div class="form-horizontal">
    <h4>Student</h4>
    <hr />

    //Returns an unordered list (ul element) of validation messages that are in the ModelStateDictionary object.
    @Html.ValidationSummary(true, "", new { @class = "text-danger" })

    <div class="form-group">
        //Returns an HTML label element and the property name of the property that is represented by the specified expression.            
        @Html.LabelFor(model => model.LastName, htmlAttributes: new { @class = "control-label col-md-2" })

        <div class="col-md-10">
            //Returns an HTML input element for each property in the object that is represented by the Expression expression.
            @Html.EditorFor(model => model.LastName, new { htmlAttributes = new { @class = "form-control" } })

            //Returns the HTML markup for a validation-error message for each data field that is represented by the specified expression.
            @Html.ValidationMessageFor(model => model.LastName, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.FirstMidName, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.FirstMidName, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.FirstMidName, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.EnrollmentDate, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.EnrollmentDate, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.EnrollmentDate, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        <div class="col-md-offset-2 col-md-10">
            <input type="submit" value="Create" class="btn btn-default" />
        </div>
    </div>
</div>
}

<div>
    //Returns an anchor element (a element) the text is Back to List and action is Index
    @Html.ActionLink("Back to List", "Index")
</div>

Detalles - parte del controlador

Al ser url ~/Student/Details/5 : (~: raíz del sitio, Student: Controller, Details: Action, 5: student id), es posible recuperar al alumno por su id.

// GET: Student/Details/5
    public ActionResult Details(int? id)
    {
        // it good practice to consider that things could go wrong so,it is wise to have a validation in the controller
        if (id == null)
        {
            // return a bad request
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
        }
        Student student = db.Students.Find(id);
        if (student == null)
        {
            // if doesn't found return 404
            return HttpNotFound();
        }
        return View(student);
    }

Detalles - Ver parte

// Model is the class that contains the student data send by the controller and will be rendered in the view
@model ContosoUniversity.Models.Student   

<h2>Details</h2>

<div>
   <h4>Student</h4>
<hr />
<dl class="dl-horizontal">
    <dt>
        //Gets the display name for the model.
        @Html.DisplayNameFor(model => model.LastName)
    </dt>

    <dd>
        //Returns HTML markup for each property in the object that is represented by the Expression expression.
        @Html.DisplayFor(model => model.LastName)
    </dd>

    <dt>
        @Html.DisplayNameFor(model => model.FirstMidName)
    </dt>

    <dd>
        @Html.DisplayFor(model => model.FirstMidName)
    </dd>

    <dt>
        @Html.DisplayNameFor(model => model.EnrollmentDate)
    </dt>

    <dd>
        @Html.DisplayFor(model => model.EnrollmentDate)
    </dd>
    <dt>
        @Html.DisplayNameFor(model => model.Enrollments)
    </dt>
    <dd>
        <table class="table">
            <tr>
                <th>Course Title</th>
                <th>Grade</th>
            </tr>
            @foreach (var item in Model.Enrollments)
            {
                <tr>
                    <td>
                        @Html.DisplayFor(modelItem => item.Course.Title)
                    </td>
                    <td>
                        @Html.DisplayFor(modelItem => item.Grade)
                    </td>
                </tr>
            }
        </table>
    </dd>
</dl>
</div>
<p>
    //Returns an anchor element (a element) the text is Edit, action is Edit and the route value is the model ID property.
    @Html.ActionLink("Edit", "Edit", new { id = Model.ID }) |
    @Html.ActionLink("Back to List", "Index")
</p>

Editar - parte del controlador

 // GET: Student/Edit/5
 // It is receives a get http request for the controller Student and Action Edit with the id of 5
    public ActionResult Edit(int? id)
    {
         // it good practice to consider that things could go wrong so,it is wise to have a validation in the controller
        if (id == null)
        {
            // returns a bad request
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
        }
        
        // It finds the Student to be edited.
        Student student = db.Students.Find(id);
        if (student == null)
        {
            // if doesn't found returns 404
            return HttpNotFound();
        }
        // Returns the Student data to fill out the edit form values.
        return View(student);
    }

Este método es muy similar al método de acción de detalles, que es un buen candidato para una refactorización, pero está fuera del alcance de este tema.

    // POST: Student/Edit/5
    [HttpPost]

    //used to To protect from overposting attacks more details see http://stackoverflow.com/documentation/asp.net-mvc/1997/html-antiforgerytoke
    [ValidateAntiForgeryToken]

    //Represents an attribute that is used for the name of an action.
    [ActionName("Edit")]
    public ActionResult Edit(Student student)
    {
        try
        {
            //Gets a value that indicates whether this instance received from the view is valid.
            if (ModelState.IsValid)
            {
                // Two thing happens here:
                // 1) db.Entry(student) -> Gets a DbEntityEntry object for the student entity providing access to information about it and the ability to perform actions on the entity.
                // 2) Set the student state to modified, that means that the student entity is being tracked by the context and exists in the database, and some or all of its property values have been modified.
                db.Entry(student).State = EntityState.Modified;

                // Now just save the changes that all the changes made in the form will be persisted.
                db.SaveChanges();

                // Returns an HTTP 302 response to the browser, which causes the browser to make a GET request to the specified action, in this case the index action.
                return RedirectToAction("Index");
            }
        }
        catch
        {
            //Log the error add a line here to write a log.
            ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists, see your system administrator.");
        }

        // return the invalid student instance to be corrected.
        return View(student);
    }

Eliminar - parte del controlador

Es una buena práctica resistir la tentación de realizar la acción de eliminación en la solicitud de obtención. Sería un gran error de seguridad, se debe hacer siempre en el método posterior.

    // GET: Student/Delete/5
    public ActionResult Delete(int? id)
    {
        // it good practice to consider that things could go wrong so,it is wise to have a validation in the controller
        if (id == null)
        {
            // returns a bad request
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
        }

        // It finds the Student to be deleted.
        Student student = db.Students.Find(id);
        if (student == null)
        {
            // if doesn't found returns 404
            return HttpNotFound();
        }
        // Returns the Student data to show the details of what will be deleted.
        return View(student);
    }

    // POST: Student/Delete/5
    [HttpPost]

    //Represents an attribute that is used for the name of an action.
    [ActionName("Delete")]

    //used to To protect from overposting attacks more details see http://stackoverflow.com/documentation/asp.net-mvc/1997/html-antiforgerytoke
    [ValidateAntiForgeryToken]
    public ActionResult Delete(int id)
    {
        try
        {
            // Finds the student
            Student student = db.Students.Find(id);

            // Try to remove it
            db.Students.Remove(student);

            // Save the changes
            db.SaveChanges();
        }
        catch
        {
            //Log the error add a line here to write a log.
            ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists, see your system administrator.");
        }

        // Returns an HTTP 302 response to the browser, which causes the browser to make a GET request to the specified action, in this case the index action.
        return RedirectToAction("Index");
    }