MVC HttpGet Attribute - asp.net-mvc

Question

MVC noob here and cannot find a simple enough explanation from this.
I just started working on a fairly large app built with MVC.
In the controller I'm using, most of the ActionResults have the [HttpGet] attribute appended to them. So I'm building off that code, and I built two ActionResults myself but left the [HttpGet] attributes off.
These make calls out to the database layer and then return results to the view. They work fine. When I noticed they didn't have [HttpGet] on them, I added them and then the calls stopped working. I can't figure out why, or the rhyme and reason for when they have to be there.
Here's a call I'm making from the view:
function getExcelExport() {
var activePane = $('div.tab-pane.active');
var agencyCompany = $(activePane).find('#Agency_AgencyId').val();
if (!$(activePane).find('#form0').valid()) { return false; }
var month = $(activePane).find('#CommissionMonth').val();
var year = $(activePane).find('#CommissionYear').val();
window.location = 'AgencyManagement/GetCommissionsExcel?agencyID=' + agencyCompany + '&month=' + month + '&year=' + year;
};
and here's the action in the controller:
public ActionResult GetCommissionsExcel(string agencyid, string month, string year)
{
try
{
var as400rep = new iSeriesRepository(new iSeriesContext());
var results = as400rep.GetCommissionExcel(agencyid, month, year);
string xml = String.Empty;
XmlDocument xmlDoc = new XmlDocument();
XmlSerializer xmlSerializer = new XmlSerializer(results.GetType());
using (System.IO.MemoryStream xmlStream = new System.IO.MemoryStream())
{
xmlSerializer.Serialize(xmlStream, results);
xmlStream.Position = 0;
xmlDoc.Load(xmlStream);
xml = xmlDoc.InnerXml;
}
var fName = string.Format("CommissionsExcelExport-{0}", DateTime.Now.ToString("s"));
fName = fName + ".xls";
byte[] fileContents = System.Text.Encoding.UTF8.GetBytes(xml);
return File(fileContents, "application/vnd.ms-excel", fName);
}
catch (Exception ex)
{
Log.Error(ex.Message, ex.InnerException);
throw;
}
}
Is there a simple explanation for this?

Answer 1

The reason that when you added [HttpGet] and the calls 'stopped' working is because you would be calling the method using a different HTTP verb e.g. POST.
Applying a Http verb attribute on a method means, to restrict an action method so that the method handles only HTTP GET requests.
The reason why it all worked when you did not use a http verb attribute is because that action method is then available via all Http verbs.
Mark that Action Method with [HttpPost] and it will work.
[HttpPost]
public ActionResult Action(int id)
{
}
You are able to have the same Method name for a GET and a POST, but the method requires a different signature (overloading).
[HttpGet]
public ActionResult Action() { }
[HttpPost]
public ActionResult Action(int id) { }
This is usually used in a PRG pattern (POST, Redirect, GET). You can read further about this here

Answer 2

[HttpGet] marks the Action as application only for GET requests -
Consider the following:
public ActionResult DoSomething() { }
if you were to GET to /DoSomething OR POST /DoSomething - the action would be invoked.
Specifying:
[HttpGet]
public ActionResult DoSomething() { }
ensures this is only going to be called if the request was a GET