问题
In Short: How do I successfully edit a DB entry without needing to include every single field for the Model inside of the Edit View?
UPDATE
So I have an item in the DB (an Article). I want to edit an article. The article I edit has many properties (Id, CreatedBy, DateCreated, Title, Body). Some of these properties never need to change (like Id, CreatedBy, DateCreated). So in my Edit View, I only want input fields for fields that can be changed (like Title, Body). When I implement an Edit View like this, Model Binding fails. Any fields that I didn't supply an input for gets set to some 'default' value (like DateCreated gets set to 01/01/0001 12:00:00am). If I do supply inputs for every field, everything works fine and the article is edited as expected. I don't know if it's correct in saying that "Model Binding fails" necessarily, so much as that "the system fills in fields with incorrect data if no Input field was supplied for them in the Edit View."
How can I create an Edit View in such a way that I only need to supply input fields for fields that can/need editing, so that when the Edit method in the Controller is called, fields such as DateCreated are populated correctly, and not set to some default, incorrect value? Here is my Edit method as it currently stands:
[HttpPost]
public ActionResult Edit(Article article)
{
// Get a list of categories for dropdownlist
ViewBag.Categories = GetDropDownList();
if (article.CreatedBy == (string)CurrentSession.SamAccountName || (bool)CurrentSession.IsAdmin)
{
if (ModelState.IsValid)
{
article.LastUpdatedBy = MyHelpers.SessionBag.Current.SamAccountName;
article.LastUpdated = DateTime.Now;
article.Body = Sanitizer.GetSafeHtmlFragment(article.Body);
_db.Entry(article).State = EntityState.Modified;
_db.SaveChanges();
return RedirectToAction("Index", "Home");
}
return View(article);
}
// User not allowed to edit
return RedirectToAction("Index", "Home");
}
And the Edit View if it helps:
. . .
@using (Html.BeginForm()) {
@Html.ValidationSummary(true)
<fieldset>
<legend>Article</legend>
<p>
<input type="submit" value="Save" /> | @Html.ActionLink("Back to List", "Index")
</p>
@Html.Action("Details", "Article", new { id = Model.Id })
@Html.HiddenFor(model => model.CreatedBy)
@Html.HiddenFor(model => model.DateCreated)
<div class="editor-field">
<span>
@Html.LabelFor(model => model.Type)
@Html.DropDownListFor(model => model.Type, (SelectList)ViewBag.Categories)
@Html.ValidationMessageFor(model => model.Type)
</span>
<span>
@Html.LabelFor(model => model.Active)
@Html.CheckBoxFor(model => model.Active)
@Html.ValidationMessageFor(model => model.Active)
</span>
<span>
@Html.LabelFor(model => model.Stickied)
@Html.CheckBoxFor(model => model.Stickied)
@Html.ValidationMessageFor(model => model.Stickied)
</span>
</div>
<div class="editor-label">
@Html.LabelFor(model => model.Title)
</div>
<div class="editor-field">
@Html.EditorFor(model => model.Title)
@Html.ValidationMessageFor(model => model.Title)
</div>
<div class="editor-label">
@Html.LabelFor(model => model.Body)
</div>
<div class="editor-field">
@* We set the id of the TextArea to 'CKeditor' for the CKeditor script to change the TextArea into a WYSIWYG editor. *@
@Html.TextAreaFor(model => model.Body, new { id = "CKeditor", @class = "text-editor" })
@Html.ValidationMessageFor(model => model.Body)
</div>
</fieldset>
. . .
If I were to leave out these two inputs:
@Html.HiddenFor(model => model.CreatedBy)
@Html.HiddenFor(model => model.DateCreated)
when the Edit method is called, they're set to default values. CreatedBy is set to Null, Created is set to 01/01/0001 12:00:00am
Why are they not set to the values as they are currently set to in the DB?
回答1:
After yet some more research I came upon some tools that assist in the ViewModel process - one being AutoMapper & the other InjectValues. I went with InjectValues primarily because it can not only "flatten" objects (map object a -> b) but it can also "unflatten" them (map object b -> a) - something that AutoMapper unfortunately lacks out-of-the-box - something I need to do in order to update values inside of a DB.
Now, instead of sending my Article model with all of its properties to my views, I created an ArticleViewModel containing only the following properties:
public class ArticleViewModel
{
public int Id { get; set; }
[MaxLength(15)]
public string Type { get; set; }
public bool Active { get; set; }
public bool Stickied { get; set; }
[Required]
[MaxLength(200)]
public string Title { get; set; }
[Required]
[AllowHtml]
public string Body { get; set; }
}
When I Create an Article, instead of sending an Article object (with every property) I send the View a 'simpler' model - my ArticleViewModel:
//
// GET: /Article/Create
public ActionResult Create()
{
return View(new ArticleViewModel());
}
For the POST method we take the ViewModel we sent to the View and use its data to Create a new Article in the DB. We do this by "unflattening" the ViewModel onto an Article object:
//
// POST: /Article/Create
public ActionResult Create(ArticleViewModel articleViewModel)
{
Article article = new Article(); // Create new Article object
article.InjectFrom(articleViewModel); // unflatten data from ViewModel into article
// Fill in the missing pieces
article.CreatedBy = CurrentSession.SamAccountName; // Get current logged-in user
article.DateCreated = DateTime.Now;
if (ModelState.IsValid)
{
_db.Articles.Add(article);
_db.SaveChanges();
return RedirectToAction("Index", "Home");
}
ViewBag.Categories = GetDropDownList();
return View(articleViewModel);
}
The "missing pieces" filled in are Article properties I didn't want to set in the View, nor do they need to be updated in the Edit view (or at all, for that matter).
The Edit method is pretty much the same, except instead of sending a fresh ViewModel to the View we send a ViewModel pre-populated with data from our DB. We do this by retrieving the Article from the DB and flattening the data onto the ViewModel. First, the GET method:
//
// GET: /Article/Edit/5
public ActionResult Edit(int id)
{
var article = _db.Articles.Single(r => r.Id == id); // Retrieve the Article to edit
ArticleViewModel viewModel = new ArticleViewModel(); // Create new ArticleViewModel to send to the view
viewModel.InjectFrom(article); // Inject ArticleViewModel with data from DB for the Article to be edited.
return View(viewModel);
}
For the POST method we want to take the data sent from the View and update the Article stored in the DB with it. To do this we simply reverse the flattening process by 'unflattening' the ViewModel onto the Article object - just like we did for the POST version of our Create method:
//
// POST: /Article/Edit/5
[HttpPost]
public ActionResult Edit(ArticleViewModel viewModel)
{
var article = _db.Articles.Single(r => r.Id == viewModel.Id); // Grab the Article from the DB to update
article.InjectFrom(viewModel); // Inject updated values from the viewModel into the Article stored in the DB
// Fill in missing pieces
article.LastUpdatedBy = MyHelpers.SessionBag.Current.SamAccountName;
article.LastUpdated = DateTime.Now;
if (ModelState.IsValid)
{
_db.Entry(article).State = EntityState.Modified;
_db.SaveChanges();
return RedirectToAction("Index", "Home");
}
return View(viewModel); // Something went wrong
}
We also need to change the strongly-typed Create & Edit views to expect an ArticleViewModel instead of an Article:
@model ProjectName.ViewModels.ArticleViewModel
And that's it!
So in summary, you can implement ViewModels to pass just pieces of your Models to your Views. You can then update just those pieces, pass the ViewModel back to the Controller, and use the updated information in the ViewModel to update the actual Model.
回答2:
View model example:
public class ArticleViewModel {
[Required]
public string Title { get; set; }
public string Content { get; set; }
}
Binding example
public ActionResult Edit(int id, ArticleViewModel article) {
var existingArticle = db.Articles.Where(a => a.Id == id).First();
existingArticle.Title = article.Title;
existingArticle.Content = article.Content;
db.SaveChanges();
}
That is simple example, but you should look at ModelState to check if model doesn't have errors, check authorization and move this code out of controller to service classes, but that is another lesson.
This is corrected Edit method:
[HttpPost]
public ActionResult Edit(Article article)
{
// Get a list of categories for dropdownlist
ViewBag.Categories = GetDropDownList();
if (article.CreatedBy == (string)CurrentSession.SamAccountName || (bool)CurrentSession.IsAdmin)
{
if (ModelState.IsValid)
{
var existingArticle = _db.Articles.First(a => a.Id = article.Id);
existingArticle.LastUpdatedBy = MyHelpers.SessionBag.Current.SamAccountName;
existingArticle.LastUpdated = DateTime.Now;
existingArticle.Body = Sanitizer.GetSafeHtmlFragment(article.Body);
existingArticle.Stickied = article.Stickied;
_db.SaveChanges();
return RedirectToAction("Index", "Home");
}
return View(article);
}
// User not allowed to edit
return RedirectToAction("Index", "Home");
}
回答3:
another good way without viewmodel
// POST: /Article/Edit/5
[HttpPost]
public ActionResult Edit(Article article0)
{
var article = _db.Articles.Single(r => r.Id == viewModel.Id); // Grab the Article from the DB to update
article.Stickied = article0.Stickied;
// Fill in missing pieces
article.LastUpdatedBy = MyHelpers.SessionBag.Current.SamAccountName;
article.LastUpdated = DateTime.Now;
if (ModelState.IsValid)
{
_db.Entry(article0).State = EntityState.Unchanged;
_db.Entry(article).State = EntityState.Modified;
_db.SaveChanges();
return RedirectToAction("Index", "Home");
}
return View(article0); // Something went wrong
}
回答4:
Use ViewModels.
Through my continued research of finding a solution to this issue I believe that using these things called "ViewModels" is the way to go. As explained in a post by Jimmy Bogard, ViewModels are a way to "show a slice of information from a single entity."
asp.net-mvc-view-model-patterns got me headed on the right track; I'm still checking out some of the external resources the author posted in order to further grasp the ViewModel concept (The blog post by Jimmy being one of them).
回答5:
In addition to the answer, AutoMapper can also be used to unflatten it. Using AutoMapper to unflatten a DTO
来源：https://stackoverflow.com/questions/10935803/successful-model-editing-without-a-bunch-of-hidden-fields