ASP.NET MVC 4.0 model binder not working with collection

Question

The default model binder is not mapping the collections in my model. Here is my code:

Model:

public class Company
{
   public string Name;
   public List<CompanyActivity> Activities
}

public class CompanyActivity
{
   public string  Code;
   public string Description
}

Controller:

[HttpPost]
public ActionResult Index(Company company) {}

View/HTML:

<input name="Name" type="text" value="some name" />
<input name="Activities[0].Code" type="text" value="1" />
<input name="Activities[0].Description" type="text" value="a" />
<input name="Activities[1].Code" type="text" value="2" />
<input name="Activities[1].Description" type="text" value="b" />

The Name input is mapped but the Activities list is empty.

The HTML you've given shows the value="" attribute as empty. What happens when you provide values? Also, what is your MVC view source? — Dai
– Dai, Commented Jan 16, 2014 at 8:14

Community · Accepted Answer · 2017-05-23 11:57:38Z

1

You have defined your model with fields, but you have to use properties. You only have to change your model for this:

public class Company
{
    public string Name { get; set; }
    public List<CompanyActivity> Activities { get; set; }
}

public class CompanyActivity
{
    public string Code { get; set; }
    public string Description { get; set; }
}

Differences between fields and properties: Difference between Property and Field in C# 3.0+ and ASP.net MVC - Model binding excludes class fields?

edited May 23, 2017 at 11:57

CommunityBot

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answered Jan 16, 2014 at 9:01

Carlos Corral Carvajal

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2 Comments

Carlos Corral Carvajal Over a year ago

why? I have created a proyect with your code. Without properties dont bind and with properties bind properly. The HTML is right, like I said I have only added the {get;set;} and it works fine.

Oliver Over a year ago

Interesting I didn't realize the modelbinder was smart enough to do this using that name syntax. My answer is not nearly as neat in comparison.

Oliver · Accepted Answer · 2014-01-16 08:21:21Z

0

The names need to be identical for it to build them as a collection/array:

I would create a ViewModel to handle this case, this is why I almost always build a ViewModel to handle view rendering and the idiosyncrasies of MVC.

Model

public class Company
{
   public string Name;
   public List<CompanyActivity> Activities
}

ViewModel

public class CompanyViewModel
{
   public string Name;

   //View specific
   public List<int> CompanyActivityCodes
}

View

<input name="Name" type="text" value="" />
<input name="CompanyActivityCodes" type="text" value="" />
<input name="CompanyActivityCodes" type="text" value="" />

This will then bind the CompanyActivityCodes property, you can then reassign these to build up the Activities property in the controller.

public ActionResult Index(CompanyViewModel companyViewModel) 
{
  var company = new Company { Name = companyViewModel }; 
  company.Activities = companyViewModel.CompanyActivityCodes.Select(x =>  new CompanyActivity { Code = x });
}

answered Jan 16, 2014 at 8:21

Oliver

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3 Comments

jlp Over a year ago

I have updated my code. Activities is a list of objects, not a list of ints.

Oliver Over a year ago

yes but it's not that clever where it can figure out the nested properties when using collections.

Oliver Over a year ago

I understand, the modelbinder is not advanced enough however to figure out the nested properties when working with collections. For this reason I created a ViewModel which essentially "flattens" you CompanyActivity class into a flat class. As you see I have named the property CompanyActivityCodes as it flattens the code property in the activities collection. You've edited the question to include additional properties which complicates matters.

Vova Bilyachat · Accepted Answer · 2014-01-16 08:24:52Z

0

it shoould be

<input name="company.Activities[0].Code" type="text" value="" />

answered Jan 16, 2014 at 8:24

Vova Bilyachat

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