Liftweb: create a form that can be submitted both traditionally and with AJAX_问答_开发者

Is it possible in Lift web framework to create forms (and links) that react via AJAX, but also work without Javascript support? If so, how?

When I build the form using <lift:form.ajax>, the form's action is set to javascript:// so that it no longer submits without JS. If I build the form without explicit AJAX support, I don't know how to insert the AJAX funct开发者_如何学Pythonionality.

I suppose I could build a RESTful interface (we'll have to build that anyway) and write custom Javascript to submit the form through that. I would like to avoid code duplication, though: if it is possible to handle all three inputs (RESTful, traditional HTTP POST, AJAX) with the same code, that would be best.

Take a look at http://demo.liftweb.net/form_ajax

FormWithAjax.scala

class FormWithAjax extends StatefulSnippet {
   private var firstName = ""
   private var lastName = ""
   private val from = S.referer openOr "/"

def dispatch = {
   case _ => render _
}

def render(xhtml: NodeSeq): NodeSeq =
{
   def validate() {
      (firstName.length, lastName.length) match {
         case (f, n) if f < 2 && n < 2 => S.error("First and last names too short")
         case (f, _) if f < 2 => S.error("First name too short")
         case (_, n) if n < 2 => S.error("Last name too short")
         case _ => S.notice("Thanks!"); S.redirectTo(from)
      }
   }

   bind( "form", xhtml, 
      "first" -> textAjaxTest(firstName, s => firstName = s, s => {S.notice("First name "+s); Noop}),
      "last" -> textAjaxTest(lastName, s => lastName = s, s => {S.notice("Last name "+s); Noop}),
      "submit" -> submit("Send", validate _)
   )
}

form_ajax.html

<lift:surround with="default" at="content">
  Enter your first and last name:<br>
  <form class="lift:FormWithAjax?form=post">
      First Name: <form:first></form:first>
      Last Name: <form:last></form:last>
      <form:submit></form:submit>
   </form>
</lift:surround>

And this will work without javascript:

<form action="/form_ajax" method="post">
   <input name="F1069091373793VHXH01" type="hidden" value="true">
   First Name: <input value="" type="text" name="F1069091373788OVAAWQ" onblur="liftAjax.lift_ajaxHandler('F1069091373789N2AO0C=' + encodeURIComponent(this.value), null, null, null)">
   Last Name: <input value="" type="text" name="F1069091373790VANYVT" onblur="liftAjax.lift_ajaxHandler('F1069091373791CJMQDY=' + encodeURIComponent(this.value), null, null, null)">
   <input name="F1069091383792JGBYWE" type="submit" value="Send">
</form>

I dont know a lot about Lift so my answer focuses on alternate way to do it. This is jQuery based and will do with AJAX when Javascript is usable and traditional POST if there is no Javascript support enabled.

Form:

<form id="ajaxform" action="formhandler.php" method="post" enctype="multipart/form-data" >

<input name="firstname" type="text" />
<input name="email" type="email" />
<input name="accept" type="submit" value="Send" />

</form>

<div id="result"></div>

JS:

note: jQuery $.ajax() sends as application/x-www-form-urlencoded by default, it may be good to set form enctype="application/x-www-form-urlencoded" too.

$("#ajaxform").submit(function(e){

  // Alternative way to prevent default action:
  e.preventDefault();

  $.ajax({
    type: 'POST',
    url: 'formhandler.php',
    // Add method=ajax so in server side we can check if ajax is used instead of traditional post:
    data: $("#ajaxform").serialize()+"&method=ajax",
    success: function(data){ // formhandler.php returned some data:
      // Place returned data <div id="result">here</div>
      $("#result").html(data);
    }
  });

  // Prevent default action (reposting form without ajax):
  return false;
});

Server side (PHP)

<?php

if (isset($_POST['method']) && $_POST['method'] == 'ajax') {
  // AJAX is used this time, only #result div is updating in this case.
} else {
  // Traditional POST is used to send data, whole page is reloading. Maybe send <html><head>... etc.
}

?>

What About REST then?

This is something you should decide to use or to not use, it is not something to support as alternate to other methods (ajax, traditional) but more something integrate within other methods. Of course you can always enable or disable REST feature. You can always make form method="POST/GET/PUT/DELETE" and ajax call RESTful:

...
  $.ajax({
    type: 'PUT',
    url: 'formhandler.php',
...

...
  $.ajax({
    type: 'DELETE',
    url: 'formhandler.php',
...

But REST asks us to use XML, JSON, ... for requests too

Well, that is not well supported by browsers (without Javascript) but $.ajax() uses application/x-www-form-urlencoded as default encoding.

Ofcourse, with Javascript one can always convert data container to XML or JSON ... Here's how it can be done with jQuery, JSON object:

/* This is function that converts elements to JSON object,
 * $.fn. is used to add new jQuery plugin serializeObject() */
$.fn.serializeObject = function()
{
   var o = {};
   var a = this.serializeArray();
   $.each(a, function() {
       if (o[this.name]) {
           if (!o[this.name].push) {
               o[this.name] = [o[this.name]];
           }
           o[this.name].push(this.value || '');
       } else {
           o[this.name] = this.value || '';
       }
   });
   return o;
};

But I want one AJAX call that does everything:

You are right, computers should do our work. It's what they are designed for.

So, another thing that needs to be done is to check what http method our original html form wants to use and adapt it to send ajax requests with same method that would be used without javascript support. This is modified version from under JS: heading used earlier:

...
  // Alternative way to prevent default action:
  e.preventDefault();

  // Find out what is method that form wants to use and clone it:
  var restmethod = $('#ajaxform').attr('method');

  // Put form data inside JSON object:
  var data = $('#orderform').serializeObject();
  // Add method=ajax so in server side we can check if ajax is used instead of traditional post:
  data.method = 'ajax';

  $.ajax({
    type: restmethod, // Use method="delete" for ajax if so defined in <form ...>
    url: 'formhandler.php',
    data: data, // data is already serialized as JSON object
...

Now, our AJAX handler sends data as JSON object using method (post|get|put|delete) that is defined at <form method="put" ...>, if form method changes then our ajax handler will adapt changes too.

That's all, some code tested and is actually in use, some is not tested at all but should work.