Remote Validation for LIST of MODELs

Question

I used the following tutorial: http://msdn.microsoft.com/en-us/library/gg508808%28VS.98%29.aspx

And everything seemed fine, but in my case, string Username always comes back null. After tonnes of research, I found everyone discovered BIND Prefixes. That would be great in many circumstances, but not this one. I should note all properties and names line up, however in my for loop, the EditorFor creates a [i].Username field and this doesn't map to any model property.

QUESTION: I think I want to map [i].Username to Username where i is any number from 0-infinity, so when it GETS, the value is passed to the Action properly. How do I do this? If this is wrong, what do I do validate this for a specific row in a table?

@for (var i = 0; i < Model.Count; i++)
{
  BLAH BLAH BLAH CODE FOR BUILDING TABLE ROWS
  <td>
     @Html.EditorFor(modelItem => Model[i].Username)
  </td>                               
}

Since I could technically have HUNDREDS if not THOUSANDS of records, I would rather not had a binding PREFIX for all 1000. Am I fundamentally missing something here? I am new to ASP.NET MVC and am used to WebForms so I feel like sometimes I am mixing concepts and mashing up something that is entirely wrong.

EDIT: I fixed it by doing the following, but not sure if this is the best idea. I set the parameter equal to the FieldName without [i] prefix, but still retrieve the element with the [i] prefix. Javascript isn't my Forte so please let me know if it is horrible.

adapters.add("remote", ["url", "type", "additionalfields"], function (options) {
    var value = {
        url: options.params.url,
        type: options.params.type || "GET",
        data: {}
    },
        prefix = getModelPrefix(options.element.name);

    $.each(splitAndTrim(options.params.additionalfields || options.element.name), function (i, fieldName) {

        var paramName = fieldName.substr(fieldName.lastIndexOf(".") + 1);

        var actualFieldName = appendModelPrefix(fieldName, prefix)
        value.data[paramName] = function () {
            return $(options.form).find(":input").filter("[name='" + escapeAttributeValue(actualFieldName) + "']").val();
        };
    });

    setValidationValues(options, "remote", value);
});

Answer 1

You have not posted your code for the model or controller, but assuming you have a RemoteAttribute applied to property Username, for example

public class MyModel
{
  [Remote("IsValidUserName", "Person")]
  public string Username { get; set; }
}

with a method in PersonController

public JsonResult IsValidUserName(string Username)
{
  ....
}

and the view

@model List<Person>
...
@for (var i = 0; i < Model.Count; i++)
{
  @Html.EditorFor(m => m[i].Username)                           
}

This will generate html such as

<input name="[0].UserName" ... />
<input name="[1].UserName" ... />

Unfortunately the remote method in jquery-validate posts back the name and value of the element so that the ajax call looks like

$.ajax({
  url: '/Person/IsValidUserName',
  data: { [0].UserName: 'someone@somewhere.com' },
  ...

which will not bind.

I have reported this as an issue at Codeplex with a possible solution. In the meantime you can modify the remote method in jquery-validate.js file as follows

remote: function(value, element, param) {
  ....
  var data = {};
  // data[element.name] = value;
  data[element.name.substr(element.name.lastIndexOf(".") + 1)] = value; // add this

This will strip the prefix so that the posted data is

 data: { UserName: 'someone@somewhere.com' },

and will correctly bind to the method.

Answer 2

Assuming the code is formatted in the following way:
View:

@for(var i = 0; i<Model.Count; i++) {
    <div class="row">
        @Html.EditorFor(modelItem => Model[i].Username)
    </div>
}

<style>
    .valid{
        background: lime;
    }
</style>
@{await Html.RenderPartialAsync("_ValidationScriptsPartial");}

Model:

public class MyModel {
    [Remote("IsValidUserName", "Validation", HttpMethod = "POST")]
    public string Username { get; set; }
}

It is possible to use the automatic modelbinding to bind to the remote validation. If you were to use a list or array for this, the binding would fail while a Dictionary can catch this error.
Be aware however that the Key in the dictionary will be consistent with the id in the view (e.g. [5].Username will map to {Key: 5, Value: MyModel{Username:...}}) and won't be a default 0, hence the use of a Linq query.
Controller:

[HttpPost]
public JsonResult IsValidUserName(Dictionary<int,MyModel> Users) {
    return Json(Users.First().Value.Username.Contains("User"));
}