asp.net-mvc
CRUD操作

前書き

備考

作成 - コントローラパート

作成機能を実装するには、 GETとPOSTという 2つのアクションが必要です。

1. HTML要素を使用してユーザーがデータを入力できる形式を表示するビューを返すために使用されるGETアクション。ユーザーがデータを追加する前にいくつかのデフォルト値が挿入される場合は、このアクションのビューモデルプロパティに割り当てる必要があります。

2. ユーザーがフォームに入力して「保存」ボタンをクリックすると、フォームからのデータが処理されます。そのため、 POSTアクションが必要です。このメソッドは、データの管理とデータベースへの保存を行います。エラーが発生した場合は、フォームデータとエラーメッセージが格納された同じビューが、送信アクション後に発生する問題を説明します。

これら2つのステップは、コントローラクラス内の2つのCreate（）メソッド内で実装します。

    // 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);
    }

作成 - ビューパーツ

@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>

詳細 - コントローラ部

url〜 ~/Student/Details/5によって：（〜：サイトルート、学生：コントローラ、詳細：アクション、5：学生ID）、そのIDで学生を取り出すことができます。

// 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);
    }

詳細 - パーツを表示

// 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>

編集 - コントローラパート

 // 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);
    }

このメソッドは詳細アクションメソッドと非常によく似ていますが、これはリファクタリングの候補ですが、このトピックの範囲外です。

    // 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);
    }

削除 - コントローラ部分

取得要求で削除アクションを実行する誘惑に抵抗することは良い習慣です。それは巨大なセキュリティエラーであり、常にpostメソッドで行われなければならない。

    // 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");
    }