This blog post shows how to validate models containing complex types such as Objects and Lists in ASP.NET MVC 3.

In a first step we modify the properties of the model ( Models/ValidationModel.cs) and add some complex types:

public class ValidUserNameAttribue : ValidationAttribute
{
  public override bool IsValid(object value)
  {
    return (value != null && value.ToString() == "Bob");
  }
}

public class User
{
  [Required]
  [StringLength(8, MinimumLength = 3)]
  [ValidUserNameAttribue(ErrorMessage = "User name != 'Bob'")]
  [Display(Name = "User name")]
  public string UserName { get; set; }

  [Required]
  [StringLength(8, MinimumLength = 3)]
  [Display(Name = "Display name")]
  public string DisplayName { get; set; }
}

public class ValidationModel
{
  public User User { get; set; }

  public List Users { get; set; }
}

In a second step we modify the form ( Views\Home\Partial\_Form.cshtml) to add input element for the new model properties:

@model MVC3_Ajax_Form_jQuery_Validation.Models.ValidationModel

@DateTime.Now: Partial/_Form.cshtml rendered
< hr/>

@using (Html.BeginForm("Form", "Home"))
{
  <h1><em>User</em> object</h1>

  <p>
    @Html.LabelFor(m => m.User.UserName):
    @Html.EditorFor(m => m.User.UserName)
    @Html.ValidationMessageFor(m => m.User.UserName)
  </p>

  <p>
    @Html.LabelFor(m => m.User.DisplayName):
    @Html.EditorFor(m => m.User.DisplayName)
    @Html.ValidationMessageFor(m => m.User.DisplayName)
  </p>

  <h1>List of <em>User</em> objects</h1>

  for (var i = 0; i <= 1; i++)
  {
    <h2>User @i</h2>

    <p>
      @Html.LabelFor(m => m.Users[i].UserName):
      @Html.EditorFor(m => m.Users[i].UserName)
      @Html.ValidationMessageFor(m => m.Users[i].UserName)
    </p>

    <p>
      @Html.LabelFor(m => m.Users[i].DisplayName):
      @Html.EditorFor(m => m.Users[i].DisplayName)
      @Html.ValidationMessageFor(m => m.Users[i].DisplayName)
    </p>
  }

  <input type="submit" value="Submit" />
}

In a last step we adapt the “success-view” ( Views\Home\Partial\_Success.cshtml) that is shown after the data have been successfully validated on the server side:

@model MVC3_Ajax_Form_jQuery_Validation.Models.ValidationModel

< p><strong>Model is valid :)</strong></p>

< p>
  Model.User.Username: '@Model.User.UserName'<br />
  Model.User.DisplayName: '@Model.User.DisplayName'<br />
  Model.Users[0].Username: '@Model.Users[0].UserName'<br />
  Model.Users[0].DisplayName: '@Model.Users[0].DisplayName'<br />
  Model.Users[1].Username: '@Model.Users[1].UserName'<br />
  Model.Users[1].DisplayName: '@Model.Users[1].DisplayName'
</ p>

As you can see in the source code above, there is no magic; model binding and validation of complex objects and lists work out of the box in ASP.NET MVC 3.