If I'm posting some variables to a Web API method, is it possible to do this without creating a view model?
It seems that you can only bind to a single parameter (which represents the request's body), so if there are multiple variables then that necessitates a view model to contain them.
You can only have one param decorated with [FromBody], so therefore that one param must encapsulate all the data coming from the request body.
Related
I have a use case where I used different models for the GET and POST actions in my controller. This works great for my view, because most of the data goes into labels. The model for the GET method contains 10 properties, but the model for the POST method only needs 3.
This GET view renders a form, which only needs 3 of these properties, not all 10. Thus, the model for the POST method accepts a model class which contains only these 3 properties. Therefore, the ASP.Net MVC model binder populates the model class parameter on my POST method with only these 3 necessary properties, and all is well.
Here's the question: When I encounter some business rule violation in the POST method, and want to use ModelState.AddModelError, and re-display the original view, I no longer have the 7 properties that were not POSTed, as they were not part of the form, and are not part of the model class which this method takes as its parameter.
Currently, I'm calling into a builder to return an instance of the model class for the POST method, and have the GET method itself delegating to the same builder. So, in these cases, when there is some business rule violation in the POST method, I return a View("OriginalGetView", originalGetModel). How can I use ModelState.AddModelError in this case, in the POST method, if I want to send custom messages back to the view, using a completely different model class?
It seemed way too lazy to use the same model class for both the GET and POST methods, given that their needs were so different. What is the best practice here? I see a lot of people recommending to use the same model for both methods, and to POST all of the fields back from hidden form fields, but that just seems like a waste of bandwidth in the majority of cases, and it feels ugly to be sending things like "VendorName" back to the server, when I already have "VendorId".
I may be misunderstanding what you are trying to do, but make sure you aren't being penny-wise and pound foolish. I see you may only want to post the identifiers and not necessarily the descriptors. But it sounds like you have to re-display the view after posting...if so you can just access the model properties if you post the same model that is in the get. If you only post the identifiers, you have to spend time re-accessing the database to get the description values(i.e. vendorname as you describe) using the vendor id no? Wouldn't that also be extra processing? Like I said, I could be misunderstanding your post, but for consistency using the same view model for your view to get and post makes the most sense to me.
Hidden Inputs maybe the best solution here still I think, even on 2g you shouldn't create any lag unless unless the values of your Model properties are long strings or something encrypted or xml.
So your .cshtml would have this in it for the 4 properties not currently included in the form:
<form>
#Html.HiddenFor(m => m.Property1)
#Html.HiddenFor(m => m.Property2)
#Html.HiddenFor(m => m.Property3)
#Html.HiddenFor(m => m.Property4)
But you could also get the model state errors from the original posted model and recreate the ModelError state in your response model to get around using hidden inputs.
I just found this guide (not the answer with Green Checkmark but the highest upped Answer: ASP.NET MVC - How to Preserve ModelState Errors Across RedirectToAction?
Note: if you need to copy model properties from Model to another Model (of the same type or different type), in a cleaner way, check out AutoMapper.
Perhaps this could help with what you were trying to achieve - 'Model' level errors - which wouldn't need to attach to a specific field/property - but can be displayed in a Global area.
https://stackoverflow.com/a/53716648/10257093
I am having trouble grasping the MVC model. Does/Can the MVC model apply to my very simple webapp example? (Assume it uses a server to calculate and not javascript.) If it does, what is the model, what is the controller and what is the view?
Of course it applies.
The controller would be a servlet. Its role would be to get the numbers as request parameters, parse them, validate them, and compute the sum. If there is a validation problem, it would store an error message in a request attribute, and forward to the JSP page displaying the form, with the error message. If there is no problem, it would store the result in a request attribute and forward to another JSP displaying the result.
The model would be the two operands and the result of the computation: a simple Integer or Double in this case. It would also be the error message in case of a validation error.
The views would be the JSP containing the form, and populating the fields with the two operands, as well as the JSP displaying the result.
So you have the classical 3 components: the controller which handles inputs, creates a model and forwards to a view. The model which holds the data to display. The view which generates the HTML markup displaying the model.
I've got an object with a list defined inside it which points to a type that can be inherited. From what I understand MVC's default model binder will always instance the base type when reading data back in to this array from a form so by default I will have a list of base types.
So I need to use my own model binder and override CreateModel to instance a specific type (say from a hidden field). However when I do this and use
bindingContext.ValueProvider.GetValue("ModelType")
it always returns null even though through using fiddler I can see that form value Settings[0].ModelType contains my objects type and I need this value in CreateModel to instance the correct type.
Solved it. If your array objects need to be typed based on each item you need to use the following call to get "into" the array item
bindingContext.ValueProvider.GetValue(bindingContext.ModelName + ".ModelType")
I'm not sure if this is the standard way to do it. If anyone has any better suggestions feel free to add them
I am new to MVC. I have a controller ActionResult that has various incoming requests from various parties. I want this ActionResult to figure out what type of request it is, validate it, and perform several RedirectToAction.
My problem is that while I know how to bind a single model/object to an ActionResult and have the framework automatically map the variables from the request to that model's properties, I don't know how to achieve the same "automapping" functionality when I need to map the same request to several models that are completely separate from each other inside a single ActionResult. I am unable to determine what models are contained inside the request until I map them and validate them, by checking if the models' properties are not null.
Any thoughts?
You should really create different Actions. Since the models that are passed in are different you cannot bind them to the same action.
Of course, what you could do is create different action methods, and from there on just call a single method that contains all of your logic
If you have access to the different model classes you could create an interface that they implement, and use this interface as the model type in your controller method.
Then you could create a custom model binder and do your checking of properties there.
I have a quick question on scope of ModelAttributes.
Dev. Env: Spring MVC 3.1/Java 6/JSP w/JSTL for Views
In my controller, I add an attribute to the model via
model.addAttribute(“appForResubmission”, appForResubmission);
In the JSP(served out in response to a GET request) I read it’s contents as:
${appForResubmission.appId}
— works fine and the data is shown on JSP as expected.
Upon submission of the JSP, in the same controller in a different method(in response to a PUT request), I try to read the attributes from the Model for any changes and I am doing this as
#ModelAttribute(“appForResubmission”) Application app
in the method signature.
However, all I get is a new Application object when I try to interrogate the object for data. Spring’s documentation says this kind of instantiation of a new object happens when the requested attribute does not exist in the Model.
What would cause the attribute to be lost? Any ideas? I am suspecting it is a scope issue someplace but I am not sure where the problem could be.
Any pointers you could provide is greatly appreciated?
Thank you,
M. Reddy
The scope of a modelattribute is the request, internally it is just equivalent to HttpSerletRequest.setAttribute("model", model).
If you want the model to be available in a different controller you probably have two options, one is to reconstruct it, based on what you submit to the controller or using your persistent source. The second option is for specific model attributes to be added to the session using #SessionAttribute({'modelname'}), but just be careful that you have to call SessionStatus.complete to remove the model added to the session later.