I am building an ASP.NET MVC application, and I am trying to find a way where I can collect data from the user in a custom view model, try and set these values to one or more of my entities, then based on validation logic on those entities, collect error messages if any and get them back to the view. I am new to MVC and web design in general, it is therefore quite possible that I am making major conceptual errors, but I have tried to research as far as I could.
I realize that this is more work than having the view be strongly typed to the entity, where it would then be easy to have the validation errors display, as in this tutorial. However, I don't want to do this for security and because there are some places where I want to have values collected from a single view model to be set in multiple different entities.
I also realize that I could set validation rules on the view model itself, rather then on the entity, but this seems like poor architecture, as I would have to define them redundantly in different view models, and I would then be less sure whether I had prevented bad values from being persisted to the database.
My plan is therefore to have the validation rules be set on the entity itself and to have the view model as a dumb container. Then, in a different location in the application, I would apply the values from the view model to my entity(ies) in accordance my business logic. At this point, I would like my validation logic to be called. If the data is invalid, I plan on setting the error string in the custom attribute on the view model to the error from the validation logic on the entity. I am thinking it would go something like this:
public class CustomViewModel()
{
[SomeCustomValidation()] //Has a place for an error string and a boolean IsValid
String Property { get; set; }
}
public class BusinessLogic()
{
CustomViewModel TestForValidity(CustomViewModel viewModel)
{
MyEntity.Property = viewModel.Property;
// if(MyEntity.IsValid)? catch SomeSortOfException?
// collect error message, put it in the attribute on the view model, set IsValid to false
}
}
public class MyEntity()
{
[MoreCustomValidation()]
public String Property { get; set; }
}
I therefore have three questions:
When I try to pass data that does not satisfy my validation rules, will some sort of error or exception be thrown? Is there some indication I can use or collect when I try to pass in invalid data?
If there is some error or exception thrown, how can I collect the error message so I can assign it to my view model?
Most importantly, am I going about this all wrong? Can attributes not be modified at runtime, for example to include a new error message or to change IsValid to false? I know that I can use reflection to access the attributes. If I can modify them, how would I do so?
Thank you in advance for your help. I apologize if I misunderstand something big.
It seems you might be over-complicating things a bit. I think what you want to do is prevent the model binder from binding to properties that it should not be able to, as well as retaining the ability to check ModelState.IsValid when properties on your model do not meet the requirements of their validation attributes.
IMO the best way to accomplish this is through the use of what I call "strongly-typed binding filters". First define an interface with only the properties that you want the model binder to be allowed to bind on your model.
public interface INewBlogPost
{
string Title { get; set; }
string Body { get; set; }
}
Then ensure your entity inherits from the binding filter interface.
public class BlogPost : INewBlogPost
{
...
}
Next, modify your action method to create a new entity and manually invoke the model binder whilst typing it to the interface you just defined.
public ActionMethod NewBlogPost()
{
BlogPost newBlogPost = new BlogPost();
TryUpdateModel<INewBlogPost>(newBlogPost);
if (ModelState.IsValid)
{
...
}
}
Because you passed in a type when invoking the model binder via TryUpdateModel you explicitly told the model binder what type to bind to. This means that the model binder will only have access to the properties listed in the interface. Now when you pass a model into the method to be bound it will have to be of type INewBlogPost. Because your entity inherits from your binding filter interface, an instance of it will satisfy this requirement. The model binder will happily bind to the properties on the interface completely oblivious of any other properties your model object may have.
See this blog post for more information.
Aside
It is sometimes easy to run into action method ambiguity when you have two action methods with the same name; one for POST and one for GET like this:
[HttpGet]
public ActionResult NewBlogPost()
{
return View();
}
[HttpPost]
public ActionResult NewBlogPost()
{
BlogPost newBlogPost = new BlogPost();
TryUpdateModel<INewBlogPost>(newBlogPost);
if (ModelState.IsValid) { ... }
}
An easy way to fix that is to modify your POST action method to look like this:
[HttpPost]
public ActionResult NewBlogPost(FormCollection formCollection)
{
BlogPost newBlogPost = new BlogPost();
TryUpdateModel<INewBlogPost>(newBlogPost, formCollection);
if (ModelState.IsValid) { ... }
}
The MVC model binder knows how to bind the request form collection to an argument of type FormCollection so it will populate this just fine. Because your POST action now accepts an argument, it is no longer ambiguous with your GET method. You can pass this formCollection into TryUpdateModel to be used as the binding source if you wish, but you don't have to as it will default to the request form collection anyway. But since you are passing it in you may as well use it :)
Related
I'm trying to find a method of handling partial updates; A ViewModel has 5 fields, but only one field is sent in the Request (i.e. only send fields that were modified instead of posing the entire view model), since null values were not explicitly sent for the other fields, I don't think that they should be set to null. Since AutoMapper does not have any kind of support for a Bind list, it's proving difficult to find an elegant solution...
public virtual IActionResult Edit(int id, ViewModel1 viewModel)
{
var model = GetModel(id);
mapper.Map(viewModel, model);
// any field that was not posted, but exists in the ViewModel1 is now null in the model
...
}
The only approach I can think of, is to use Request.Form.Keys and Reflection to build an ExpandoObject that only contains the posted properties, then set CreateMissingTypeMaps and ValidateInlineMaps to allow AutoMapper to map the dynamic types... It just feels like this is a dirty workaround to compensate for functionality that's missing in AutoMapper... Is there a standard way of handling this?
When I put a breakpoint on a getter of a property in my view model, asp.net core model binding is reading my property value. This is before the view model is used in the actual view. Is there a reason it is doing this? Model binding should be for setting the properties on your view model from the value provider, not for reading them from your view model. Is there a way to prevent this?
Edit: Since there is a vote to close this question due to not providing steps to easily reproduce, here they are. Create the following controller in an asp.net core project:
public class TestController : Controller
{
public IActionResult Test(TestViewModel model)
{
return View(model);
}
public class TestViewModel
{
public string TestProperty
{
get
{
return "";
}
set
{
return;
}
}
}
}
If you put your break point in the getter, and a break point in the test controller action, you will see that the getter is accessed before it actually enters the controller action to be consumed by the view. It doesn't seem like properties in your view model should be read at this point. Just look for ideas on why this is happening, and if it is possible (or a good idea) to prevent this behavior. Thanks!
I'm not sure what version of MVC you're using, but in MVC version 5.2.3, the DefaultModelBinder calls the model class getters before setting the request values on each property during the binding process prior to the controller method being called. I could not figure out why it does this, but I was able to change that behavior by implementing a custom model binder based on the original DefaultModelBinder source code that removes the calls to the getters.
See a more detailed explanation and my full solution here: https://stackoverflow.com/a/54431404/10987278.
In your comments you mention you already have a custom model binder, so you might be able to just add the BindProperty(...) override from my solution to get the behavior you're after.
I have a simple form that posts a ViewModel to an Action method. Before saving the information the ModelState is checked with a standard if(ModelState.IsValid). Then a new object is created and saved. Great, it works.
Recently another dev went in and created a new view with my original ViewModel. He also added a new [Required] property to the ViewModel to make his logic work.
By doing that his logic broke my initial logic. Because my initial view doesn't use his new Required property so ModelState.IsValid check now fails and my code doesn't run.
What is the best approach to take here ? Though I don't want to but should I get rid of ModelState.IsValid check on my Post actions or can I somehow flag his new property to Not be required when used in my original views or when being posted in my action method ?
Thank you in advance.
You can use attribute [Bind(Exclude="")] in your action method like below. Then, when you submit the form, model binder will ignore that property even it is required.
[HttpPost]
public ActionResult Index([Bind(Exclude = "AdditionalProperty")]YourModel model)
{
//
}
You can derive the model from IValidatableObject, and then perform your own custom validations using
public virtual IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
}
How do I use IValidatableObject?
Edtied to add: If it were me, it would seem to make more sense to have him create an inherited model from your model, even if it only has 1 property in it. This would keep the native MVC validations working correctly with minimal effort on your part.
you have two choice(to the best of my knowledge!), first you can unbind the that required property while posting it to the action:
[HttpPost]
public ActionResult Create([Bind(Exclude = "RequiredProperty")]MyViewModel myViewModel)
{
if(ModelState.IsValid)
{
//
}
}
but you can solve this issue for your application by mapping the ViewModel to View in your get action, and send it to the view. try this great article
Here's my problem:
We have an intranet asp.net mvc 3 application with a controlled set of users. We have a Person class, that contains a large amount of information, that is initially loaded and stored in the session. The data/editing for this object spans across many screens. Basically, each screen is a subset of the Person's data.
I'm trying to take advantage of the built in model binding in asp.net mvc. Should I create a data class that binds the form data from each screen and then updates my session object using a service object?
Example below: DxFormData contains a subset of the person data and will only be used as a parameter on this method.
public ActionResult Dx(DxFormData data)
{
// Update current session Person object with data passed in if modelstate is valid
var viewModel = this.GetDxViewModel();
return View(viewModel);
}
public class DxForm Data
{
public string AdmitDx { get; set; }
public string PrinDx { get; set; }
}
I'm looking for thoughts on this approach and if there's a better solution available to me. The problem that I see, is that the person class contains all the data and I'm creating another class with a subset of that data. Obviously, duplicating the properties.
Side note: I did write a custom model binder that returned the session person for binding. However, I am continually getting errors when it attempts to bind.
I don't see problem with this approach. If you try to use the Parent class as the action parameter then in each form submit action then you will get validation errors because the model is not completely filled, so you should use view models in this case and unfortunately you can't avoid duplicating properties.
I have an ASP.Net MVC application with a model which is several layers deep containing a collection.
I believe that the view to create the objects is all set up correctly, but it just does not populate the collection within the model when I post the form to the server.
I have a piece of data which is found in the class hierarchy thus:
person.PersonDetails.ContactInformation[0].Data;
This class structure is created by LinqToSQL, and ContactInformation is of type EntitySet<ContactData>. To create the view I pass the following:
return View(person);
and within the view I have a form which contains a single text box with a name associated to the above mentioned field:
<%= Html.TextBox("person.PersonDetails.ContactInformation[0].Data")%>
The post method within my controller is then as follows:
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Create (Person person)
{
//Do stuff to validate and add to the database
}
It is at this point where I get lost as person.PersonDetails.ContactInformation.Count() ==0. So the ModelBinder has created a ContactInformation object but not populated it with the object which it should hold (i.e ContactData) at index 0.
My question is two fold:
1. Have I taken the correct approach.. i.e. should this work?
2. Any ideas as to why it might be failing to populate the ContactInformation object?
Many thanks,
Richard
I think that your model is too complex for the default model binder to work with. You could try using multiple parameters and binding them with prefixes:
public ActionResult Create(
Person person,
[Bind(Prefix="Person.PersonDetails")]
PersonDetails details,
[Bind(Prefix="Person.PersonDetails.ContactInformation")]
ContactInformation[] info )
{
person.PersonDetails = details;
person.PersonDetails.ContactInformation = info;
...
}
Or you could develop your own custom model binder that would understand how to derive your complex model from the form inputs.
If a property is null, then the model binder other could not find it or could not find values in the submitted form necessary to make an instance of the type of the property. For example, if the property has a non-nullable ID and your form does not contain any data for that ID , the model binder will leave the property as null since it cannot make a new instance of the type without knowing the ID.
In other words, to diagnose this problem you must carefully compare the data in the submitted form (this is easy to see with Firebug or Fiddler) with the structure of the object you are expecting the model binder to populate. If any required fields are missing, or if the values are submitted in such a way that they cannot be converted to the type of a required field, then the entire object will be left null.
I've been struggling with this same type of scenario and eventually came to realize that the underlying problem is that the MVC default model binder does not seem to work on EntitySet<T> fields, only List<T> fields. I did however find a simple workaround that seems acceptable. In my case, I have a Company entity that has one to many relationship to Contacts (my Linq-to-Sql EntitySet).
Since it seems that when I change my code from EntitySet<Contact> to List<Contact>, the MVC default model binder starts working as expected (even though the LTS isn't now), I figured I would provide an alternate, "aliased" property to MVC that is of type List<Contact>, and sure enough, this seems to work.
In my Company entity class:
// This is what LINQ-to-SQL will use:
private EntitySet<Contact> _Contacts = new EntitySet<Contact>();
[Association(Storage="_Contacts", OtherKey="CompanyID", ThisKey="ID")]
public EntitySet<Contact> Contacts
{
get { return _Contacts; }
set { _Contacts.Assign(value); }
}
// This is what MVC default model binder (and my View) will use:
public List<Contact> MvcContacts
{
get { return _Contacts.ToList<Contact>(); }
set { _Contacts.AddRange(value); }
}
So now, in my View, I have the following:
<label>First Name*
<%= Html.TextBox("Company.MvcContacts[" + i + "].FirstName") %>
</label>
<label>Last Name*
<%= Html.TextBox("Company.MvcContacts[" + i + "].LastName") %>
</label>
Seems to work like a charm!
Best of luck!
-Mike
Maybe lack of Bind attribute is the case:
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Create ([Bind] Person person)
{
// Do stuff to validate and add to the database
}
The first argument of Html.TextBox is the name of the textbox, the second would be the value.
"Wrong":
<%= Html.TextBox("person.PersonDetails.ContactInformation[0].Data")%>
"Right":
<%= Html.TextBox("nameoftextbox", person.PersonDetails.ContactInformation[0].Data)%>
Make sure your models (and all nested models) are using properties (getters/setters) instead of fields. Apparently the default binder needs properties to function properly. I had a very similar situation that was fixed by changing the necessary fields to properties.