I have a complex view model which has some subclasses. For the sake of a simple example, let's assume there's one subclass.
That subclass is displayed by rendering a partial view. The user can toggle that view in the interface, completely hiding the whole thing.
Now there are two valid input options:
The user chooses to hide the partial and doesn't fill in anything. The whole thing should be ignored.
The user chooses to view the partial, now he has to fill it in. Some of the fields are required, some are not.
What's a good way to handle this is MVC validation? I cannot mark the fields as Required, since the postback will post the empty values and the server side logic will say ModelState.IsValid is false beacuse there are fields missing.
Of course I can lose the [Required] attributes and do the checks manually myself, but I was wondering if there's no better way to get the same result.
The simplest way of doing this is like this ASP.NET MVC 3 Data Annotation: Add validation dynamically.
For a harder (a bit nicer) solution read this: DataAnnotations "NotRequired" attribute
Related
I have an entity with, amongst others, the fields: CreatedBy, CreatedAt, ChangedAt
Now in the view, I do not want the user to fill these fields.
My approach was to fill them on the HTTP POST Action, before ModelState.IsValid check is made and before saving the data to the database.
However, ModelState.IsValid keeps returning false no matter what. What is the right way to implement this? Should I take the validation (ModelState.IsValid) from the POST action?
One problem, many solutions (from best to worst, in my opinion).
First solution
The best way would be to use a ViewModel (a class containing only the fields which must be edited by user and / or validated).
In this case, the CreatedBy, CreatedAt, ChangedAt fields would not appear in your ViewModel class.
Second solution
If you don't want ViewModel, you can put the "not mutable by user" fields as hidden fields in your view
#Html.HiddenFor(m => m.CreatedAt)
of course, hidden fields can be changed by user, so it's always an open door to unwanted datas...
Third solution
Clean ModelState from undesired errors before checking if it's valid (should become really boring if you've many fields concerned).
if (ModelState.ContainsKey("CreatedAt")) {
ModelState["CreatedAt"].Errors.Clear();
}
//then test for ModelState.IsValid()
Other solutions
WhiteList, BlackList for model binding, or... anything I forgot !
Many projects like to separate the View Model from the Domain Model. This allows you to create a View-Model class specifically tailored for the data you want to render and/or receive in a certain action while keeping the domain model correct/consistent.
In your View-Model class you would either not define any such property as the created date (since it is not supposed to be posted but is determined in the action). Or if you use one and the same View-Model for rendering and posting, and you want to render the date, you can make the date nullable (see Alexey's answer) on the View-Model while keeping it mandatory on the domain model.
DateTime is not nullable. If you want to keep those fields as null during model binding, if there is no values for them use:
Nullable<DateTime>
or shortcut:
DateTime?
I've understood that a viewmodel in MVC is supposed to reflect data on a single page rather than objects in the model. But should the viewmodel correspond to the data you want to show on that page or to the data you want back from that page? If we for example look at a login page then I just want username and password back in the post, but I might need more variables than that when displaying the login page (previous error messages etc).
Should the viewmodel then just contain username and password as parameters and the rest of the variables end up in viewbags. Or should the viewmodel contain all values I want to show even though I'm only interested in a few of them in the response.
What is best practice when using viewmodels?
All data that somehow interacts between the html and your server should be in a ViewModel.
This allows you to perform formatting and such outside your html and inside your ViewModel properties.
However, if your page contains a lot of controls or data, you may want to split it into multiple ViewModels (example one for the Get and one for the Post).
The post model may contain only data that you entered and needs to be validated.
I think it's best to put everything in the view-model. This keeps the code cleaner and makes discovery and maintenance easier as well. The view-model should be your primary mechanism here.
I would say only properties you need, in your case username and password. If you want to display error messages then that's what ModelState is for. You can always append any error messages to your ModelState:
ModelState.AddModelError("PropertyName", "Error Text")
Beyond that let's say you have a form that contains a list of categories that you need to pick one category from a drop down. In this case I usually attach that list to my model even though the only thing being submitted is the actual selected value. But this is a matter of preference, meaning I could also set a ViewBag to contain this SelectList of categories and then bind that to your DropDownList. I suppose it's better to place this in a model because ViewBag is dynamic and you will have to cast anything in the ViewBag into it's underlying type on your views.
In our asp.net mvc I've created view with two partial views inside.
That view accepts model of some type, for example Customer.
First partial view doesn't have model because it is search form with empty field.
Second form is form with populated fields.
What I found out that on first view, if I have called input fields like properties in model and if I don't provide value for them, mvc implicitly binds values from model to the fields.
First I was thinking is some of kind of mistake, but then I've expiremented little bit with a code:
-I've added native input element with id and name called the same like model, input field is empty in browser
-If I try the same thing with Html.TextBox helper and don't provide value, mvc gets that value from my model object(by name of property/field) and in browser that field is populated.
Is this a bug or am I doing something wrong?
Thanx
That's by design.
I'd recomend reading:
http://asp.net/mvc
http://weblogs.asp.net/scottgu/archive/tags/MVC/default.aspx
and last but not least:
http://channel9.msdn.com/Events/MIX
especially mix10 has a tonn of sessions about mvc
all are good read and watch (-:
That is by design. If you send a model to a view and you're using the HTML input Helpers that come with ASP.NET MVC, they'll implicitly populate themselves from the model.
This is helpful in many situations. If you don't want this behavior, you can always NOT use the helpers or write your own simple helpers.
I'm porting an existing system to ASP.NET MVC2. In the current legacy app, the user can select from dozens of available fields to customize CRUD forms for different entities in the domain model, similar to the way ERP systems allow customization of core modules.
My question: I'm looking for a good pattern or example for this kind of behavior in ASP.NET MVC2. It seems to me it's rather like creating a ViewModel dynamically based upon user choices, or perhaps the right approach is data-driven view pages that aren't strongly-typed where I can reflect over the results client-side to determine field headings or something -- if that makes sense :). Or maybe I can drive AutoMapper or similar dynamically # runtime based on user choices?
The underlying domain model is EF4-based and I'm using a simple Repository pattern # present for the ViewModel.
TIA for any input! Michael
If I didn't find anything else that matched the needs and went on to do it custom, I would:
Use the ViewModel with all the fields / not just the ones the user picked.
Pass both the ViewModel and the view configuration to the view
Call some html helper that for each item in the configuration adds a field with the corresponding property in the model
The configuration could be passed as either part of a containing ViewModel or in a separate entry in ViewData
Depending on what you need, building/passing the view configuration could be put in an Action Filter. Alternatively the helper could pull it directly.
A different approach is if you need completely custom fields. I mean user defined fields. If that's the scenario, that's not typed at the controller level already, so I'd pass the list of fields/values to the view. The view can do a foreach on those adding the fields. Again that could be moved to a HtmlHelper.
I am wondering if there is a way to make ASP.NET controls play nicely with my ASP.NET MVC app. Here is what I am doing.
I have an order page which displays info about a single Order object. The page will normally have a bunch of rows of data, each row representing an OrderItem object. Each row is an ASP.NET User Control. On the user control there is a form element with two text boxes (Quantity and Price), and an update button.
When I click the update button, I expect the form to post the data for that individual OrderItem row to a controller method and update the OrderItem record in the database.
Here is my problem: When the post happens, the framework complains because the fields on the form don't match the parameters on the controller method. Each form field is something like "OrderItem_1$Quantity" or "OrderItem_2$Price" instead of just "Quantity" or "Price" which would match my method parameters.
I have been told that I can overcome this by making sure that the IDs of all my controls are unique for the page, but allow the NAMEs to be repeated between different forms, so that if a form for an individual row is posted, the name can be something that will match what is on my controller method.
The only problem is that I am using ASP.NET controls for my text boxes (which I REALLY want to continue doing) and I can't find any way to override the name field. There is no Name propery on an ASP.NET control, and even when I try to set it using the Attributes accessor property by saying "control.Attributes["Name"] = "Price";" it just adds another name= attribute to the HTML tag which doesn't work.
Does any one know how I can make this work? I really don't like all of the HtmlHelper functions like TextBox and DropDown because I hate having my .aspx be so PHP or ASP like with the <%%> tags and everything. Thanks!
I think you're straddled between two worlds of ASP.NET WebForms and ASP.NET MVC. You really need to use the Html.TextBox methods, etc. in MVC. This gives you complete control over the markup, which is one of the main benefits of MVC.
The very problem you're having with control over the generated HTML, e.g. getting two name attributes, is exactly what MVC is designed to address. If you stop fighting it and go with the flow, it'll work much better.
<% %> tags aren't a problem unless you have logic in there. Putting simple presentation logic on your view is fine.
If you don't like this, then maybe it's better to stick with standard ASP.NET.