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Two "forms" in one <form> clash their required attributes

The issue:
I have a single page with two email forms (one <form>, two divs inside this which look like forms to the user). When you submit either form, the C# behind looks at the values of the form and sends them in an email. This works well, and now I want a little validation, but I can't add required attributes to the inputs as the code doesn't know it's two separate "forms" and needs to handle the required attributes separately for each one.
I understand why this issue occurs, but I want to know if there's a way to tell the page to handle the required attributes in groups.
What I've tried: Both "forms" are handled by the code behind, and so need to be run server-side, so separate <form> elements wouldn't work. I have tried nesting the "forms" as <form> elements inside the server-side <form>, which separates the required attributes as desired, but seemingly breaks a number of things and I've read this is generally bad practice anyway.
What I'm not asking: To validate the form in the code behind.
Edit:
David's answer works great to validate groups of textboxes, which is what I needed.
To additionally validate a checkbox, I used javascript. onclientclick we can check if the checkbox is checked AND validate using Page_ClientValidate('validationgroup') and then return true, else return false. onclick is only fired when onclientclick returns true.

use one form with two submit buttons. Use validationgroup to distinguish
http://msdn.microsoft.com/en-us/library/ms227424(v=vs.100).aspx

if you write your own validation function for each submit button it should be possible
<input type='submit' onclick='return validateFirstButton()'/>

To validate checkboxes follow the instructions here:
http://codeclimber.net.nz/archive/2007/07/19/How-to-add-a-required-validator-to-a-CheckBoxList.aspx
Because this derives from BaseValidator you will be able to use groups. Hope this helps

MVC - Refresh View Model asynchronously via AJAX + Controller?

I've been working on filtering a list of log entries, and I'm getting close to being complete.
I'm wondering if it's possible to update the current View's model asynchronously via $.ajax().
I currently have the $.ajax() working, however it returns the entire page's HTML as opposed to a partial view, or a model itself.
Is anybody aware of a way to simply update the model on the current view?

You'd have to return the model in json format and use js templating
functionality to replace the server rendered html in the dom. –
WestDiscGolf
The above is the solution, so I'll keep it simple and use a more conventional method.

This concept doesn't really make sense. The model doesn't really exist any more once the page is rendered, until it is reinstantiated on the following POST (assuming it is reinstantiated, i.e. your controller action accepts an argument of the same type). In the meantime, it is just manifested as form fields with name properties that correspond to what were the model's properties.
You can, however, dynamically create form fields that will (if possible) be mapped back to model properties again when the form is posted.
Create a field, whose name property matches the name of your model property:
<input type="hidden" id="hdnMyProperty" name="MyProperty" />
Then use jQuery to populate the field's value:
var property = /* Your returned value here */;
$('#hdnMyProperty').val(property);
There are a couple of common ways of achieving this:
Make an AJAX request to a controller action that returns a JsonResult and dynamically create the form field(s) in your Javascript (potentially - as has been mentioned - utilizing something like Knockout).
Create a controller action that returns a PartialViewResult and dynamically insert the returned markup in the appropriate place.
When you issue the next post request, the model binder will try to map this to an appropriate property in the newly-instantiated model.

You could simply use Knockout. No need to re-invent the wheel in this case.

Append ASP.Net element via jQuery .append()

Is it possible to do something like this
$("#popupForgot").append("<asp:TextBox ID='emailTextF' runat='server' Width='200px' Text='" + $.cookie("forLogin") + "'></asp:TextBox>")
I need to append an asp.net element to a div tag which will have the cookie value as it's text. I've tried with the code above and it doesn't work.
Thank you in advance

It is not possible to do this, because asp:TextBox is rendered via server-side, whereas jQuery works on client-side.
However you can render your textbox with asp:TextBox control and then you can change its value with jQuery:
$("#emailTextF").text($.cookie("forLogin"));
UPDATE
It turns out that asp:TextBox rendered id isn't equal to id parameter (used inside asp:TextBox), try this:
$("#<%= emailTextF.ClientID %>").text($.cookie("forLogin"));

JQuery is, in the end, just JavaScript code. Javascript code runs in the client's browser.
ASP tags are a server side construct; they will be converted into <input type="Text"/> fields (or something else for multi-line textboxes) before they are sent to the client's browser.
These two are completely separate concepts that can't really interact with each other (directly).
If you want to add a textbox via JQuery it can't be an ASP textbox, it needs to be an HTML textbox. If you really do need to add an ASP textbox (you don't appear to need it from what you've shown here though) then you'll need to do a postback to the server to add it. (You could do that postback asynchronously via AJAX if you wanted.)

Your code will run in the browser, this means that you asp:TextBox will not be processed by the server. So, in short, no.

You can't do this, cause ASP.NET tags processed on the server-side, before data sends to the client.
The ways is:
-add this ASP.NET control before, and change it's value by JQuery,
-if you need to add controls dynamically, use sample html tag , and get data on server from the Form.

When do you use Html.Action over Html.Partial

I still don't get the primary purpose of Html.Action in asp.net mvc. I have been using Html.Partial every time I need to load up a partial view or wanted to split up some code in a view to clean it up.
Where does Html.Action fit into all of this (e.g. where would you want to use Html.Action and not use Html.Partial)?
Edit
The answers seem to be use Html.Action for dynamic data. I don't get this as you can use Partial Views for Dynamic data as well.
For instance if a user on my site edits a row. A ajax call is made to a method and I go grab that row from the db. I then return a parital view of a form that has all the data on it ready for editing. If an error occurs then I return a json result with the error method and my javascript consumes it and alerts the user.
If all is good then the rendered html is put into a jquery dialog and displayed to the user.
Is it because you can use the "ChildActionOnlyAttribute" that makes people use Action instead?

Ankur has the right idea but I find you can really simplify the concept down further.
For me it comes down to What versus How
If you know what you want to render but not how it's likely you'll use a partial to let it determine how to render the information.
For example, maybe your view model is for an invoice. Your invoice view model probably already has all the information you need about the invoice itself, including an enumerable of the line items on the invoice perhaps. A partial might be a good choice for the line items so that it's self contained. You already have the line items details (the what), but a partial will handle how it gets rendered (the how)
On the flip side, maybe your invoice view model has a customer ID on it but no actual customer details. Here you don't have the what, so you'd pass in the customer ID to an Action and it'll get what data it needs and pass it off to the view to render how it seems fit.
So in summary if you already have all the data you want to work with, just stick with a Partial, but if you are missing information that you need to obtain, Action would be better.
Where this get really fuzzy around the edges is when a Partial view includes the ability to retrieve it's own data via Ajax (or other technologies). In which case you might be able to get away with making that Customer details portion in my example, a Partial, and have it retrieve the data it needs Using Ajax after the client get's the response. But that's more up to you if that sort of thing even makes sense for your implementation.
Addendum:
It's worth noting that if you decide to try out ASP.NET MVC Core, ChildActions are no longer available. In which case your choices will be limited to partial views, ajax, or the newly introduced feature of Components. The last of which is similar to ChildActions, but slightly different in how they are implemented.

Perhaps an example will make this clearer.
Let's say you have a menu which appears on every page, so you put it in your layout. The menu will never change - there is just some basic navigation links, Home, About, Contact us etc, so you just use a normal partial view. This will work fine - as the content is static - you don't need to go to a database to get the data. You can just use #Html.Partial("Menu");.
Later you decide you need to change the menu so that it gets all the links from a database. You update your partial view to have a model that is a List<string> - one for each link.
Now, if you still want to just use a Partial View, every action would need to query the database to get the list of links, and every Model for every View would need to have a List<string> property for the links, so that it could pass this to the Menu Partial View. This would be a bad idea.
Instead, you would make a new Child Action GetMenuLinks() - this would query the database to get the links as a List<string>, and pass this to the Partial View. This puts the Child Action in charge of getting it's own data. This means you only need to have this query in one place, the 'About Us' action for example doesn't need to worry about getting the list of links for the menu.

Partial views
Use for sharing subsections of view markup between views. Partial views can
contain inline code, HTML helper methods, and references to other partial
views. Partial views do not invoke an action method, so they cannot be used
to perform business logic.
Child actions
Use for creating reusable UI controls or widgets that need to contain business
logic. When you use a child action, it invokes an action method, renders a
view, and injects the result into the response stream.

I use Html.Action() to load dynaimc content that I do not wish to contain in the view model (for instance, user information in a sidebar). It is very useful for keeping input and output view models identical.
Note that I always use Html.Action() in conjunction with applying the ChildActionOnlyAttribute to the controller method that I am calling so that the HTML fragment is not accessible via the URL.

Use Html.Partial when you require a subset of your view model to render the section in question--usually it is something that has to do with what you're working on. If could be a subsection of a form, a relevant content piece related to the main view etc. A partial receives its model information from the parent view.
Otherwise use Html.Action to render content that is independent of your main view, such as a navigation piece, an aside, or other distractions. Html.Action uses its own model provided by its controller, rather than provided by the parent view.

This question is answered (and elected for 149 times!) here:
Html.Partial vs Html.RenderPartial & Html.Action vs Html.RenderAction
Update
Sorry, meant to send you these postings rather
MVC Html.Partial or Html.Action\
#Html.Partial() Vs #Html.Action() - MVC Razor
Hope this helps.

Filtering Pane, ASP MVC 3

My plan is to create a a two-pane page using ASP MVC 3. The left pane should be a small filter pane and the right the main content, showing a list of objects (say products).
Initially all products will be shown since no filter is applied. When selecting "only red", only red products are shown in the list. When further selecting a price range, only products in that price range will be shown.
Functionally the plan is to implement the filtering pane as a treeview with checkboxes (to be able to drill down to more and more specific filtering options), graphically it will probably be enhanced in some way to improve usability.
What is the best way to implement the coupling between the filter pane and the main list? Everything should work server side, but should of course use javascript (jQuery) when possible for direct feedback.
The simplest way is probably to make it closely coupled solution, calling a specific Asp MVC action using a custom-built javascript (with fallback to a form post). Doable enough, sure, but how to make the solution reusable? Also it would be nice to not loose all filtering data when navigating forward and back, i suppose GET arguments is the only decent way to do that?
Are there any best practices, any guidelines or anything to base this on to make a nice modular structure for filtering.

Victor, I recently had to solved this same problem. I'm not promising it's the best way but it's pretty clear and should even work well in case JavaScript is disabled (who even does that anymore?).
Create a that calls the action with all the field-selectable search options like "only red".
To that same form, add empty, hidden value for the things not directly as fields (paging, sorting...)
Setup your form with the excellent and very easy to use JQuery.Forms (http://www.malsup.com/jquery/form/) to make you form submit via JQuery (all your form values will be passed as JSON on form submit).
Make your back/next/paging/sorting links pass their individual values via query (no-JS fallback) and use JQuery to capture their click events. The JQuery click events on those links should assign the value of the value passed by the link (page number, sort column name...) to the corresponding hidden field in the form and call submit (with thanks to Jquery.Forms will submit via AJAX).
When you configure JQuery.Forms, you can define a callback method. In the callback method take the result (the HTML returned by your action that should contained your filtered+sorted+paged result) and replace the document (or DIV if you used a partial action + view) with that.
The result is a JQuery solution that works when JS is off. You also have very minimal JS code to write other than wiring the event handlers.
I'm not sure if it will be helpful but in MVC 3 you have access to a property called IsAjax from the view so you can do specific things to server a slightly different view when called from AJAX.
Cheers