Everyone knows there is a limit to the size of the query string, right?  Well ok, maybe you didn't - but there is.  What that limit is depends on the browser.  There is a lot of conflicting information out there on the magical Google.  An RFC defines it, but no one really seems to pay attention to those anyhow.  (Are you listening Microsoft, of course you are! =]).  Anyhow, for IE, the query string length is usually around 2000 characters.

However, in most cases you're better off using a form and posting your data up to the server side that way, as the limitations on data are so large you will likely not need to worry about them.  Sometimes, query strings can also show your users just a little too much information - though I'm by no means a proponent of "security through obscurity" hiding a little bit more from your users will keep the curious ones a little more in check =).

When working with Mapguide Enterprise/Mapguide Open Source we need to grab some potentially massive XML strings from the MgMap object and pass these along to the server side for processing.  Take the selection XML from the MgMap object, even a single entity selection can use a significant portion of the characters available in the query string.  On top of that, passing this data via query string requires that the data be URL encoded, using even more of our precious query string characters.

Depending on the design of your application it may not always be feasible to define a hard coded form, or even a form defined server side using ASP.NET.  In some cases (you guessed it - my case) you may want to use javascript and do all the work on the client side to define a form and pass the data long that way.

Well you're in luck, I found a pretty nice solution (WELL, at least I'm liking it  =]).   I'm kicking myself for not realizing this long ago, but oh well.  So the following javascript function demonstrates how to build, add, populate, and submit a form on the fly using some information from the MgMap object.

   1: function postData()   

   2: {   3: //get the map   

   3: mapObj = GetMap();   

   4:  

   5: //define the new form   

   6: var newForm = document.createElement("form");   

   7: //set the method to POST - the opposite of query strings..   

   8: newForm.method="POST";  

   9:  //add the new form to the current document  

  10:  document.body.appendChild(newForm);  

  11:  

  12:  //lets get some data and add it to the form  

  13:  AddFormElement(newForm, "MapName", oMap.GetMapName());  

  14:  AddFormElement(newForm, "SID", oMap.GetSessionId());  

  15:  //be sure you escape the selection XML - or you will get an error on post about a   

  16:  //"potentially dangerous form value".  Remember on the server side to Server.UrlDecode() it  

  17:  AddFormElement(newForm, "sel", escape(oMap.GetSelectionXML()));  

  18:  

  19:  //lets create our new window  

  20:  var szTarget = "targetWin"  

  21:  newForm.target = szTarget;  

  22:  //set the name/path of the ASPX file you want to process your form with  

  23:  newForm.action = "/url_to_open/file.aspx"  

  24:  

  25:  //open a new window to submit the form to.  Its a good idea to have a blank.htm so you don't get a file not found error  

  26:  var oWin = window.open("blank.htm",szTarget,'menubar=yes, resizable=yes,scrollbars=yes, status=no,toolbar=no,width=300, height=300');  

  27:  

  28:  //give the window focus.  Users like this  

  29:  oWin.focus();  

  30:  

  31:  //submit the form - it will now open in the new window  

  32:  newForm.submit();  

  33:  //remove the form from the document, we're done with it  

  34:  document.body.removeChild(newForm);  

  35:  }  

  36:  

  37:  function AddFormElement(form, elementName, elementVal)  

  38:  {  

  39:      var newElement = document.createElement("<input name='" + elementName + "' type='hidden'/>");  

  40:      newElement.value = elementVal;  

  41:      form.appendChild(newElement);  

  42:      return form;  

  43:  }

On the server side, you can now access this data from ASP.NET using Request.Form, for example Request.Form("MapName") would give you the map name.  Don't forget when retrieving the selection XML to run that through Server.UrlDecode, or HttpUtility.UrlDecode.

As usual, any comments, bugs, or rotten fruit - send em my way.  Enjoy!