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287 lines
9.4 KiB
ReStructuredText
287 lines
9.4 KiB
ReStructuredText
.. _simple_ajax:
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Example Application: Simple AJAX
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================================
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This guide will walk you through building a simple Pecan web application that uses AJAX to fetch JSON data from a server.
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Project Setup
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-------------
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First, you'll need to install Pecan:
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::
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$ pip install pecan
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Use Pecan's basic template support to start a new project:
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::
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$ pecan create myajax
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$ cd myajax
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Install the new project in development mode:
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::
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$ python setup.py develop
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Adding JavaScript AJAX Support
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------------------------------
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For this project we will need to add `jQuery <http://jquery.com/>`_ support. To add jQuery go into the ``templates`` folder and edit the ``layout.html`` file.
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Adding jQuery support is easy, we actually only need one line of code:
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.. code-block:: html
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<script src="http://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js"></script>
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The JavaScript to make the AJAX call is a little more in depth but shouldn't be unfamiliar if you've ever worked with jQuery before.
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The ``layout.html`` file will look like this:
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.. code-block:: html
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<html>
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<head>
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<title>${self.title()}</title>
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${self.style()}
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${self.javascript()}
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</head>
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<body>
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${self.body()}
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</body>
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</html>
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<%def name="title()">
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Default Title
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</%def>
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<%def name="style()">
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<link rel="stylesheet" type="text/css" media="screen" href="/css/style.css" />
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</%def>
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<%def name="javascript()">
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<script src="http://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js"></script>
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<script language="text/javascript" src="/javascript/shared.js"></script>
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<script>
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function onSuccess(data, status, jqXHR) {
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// Use a template or something here instead
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// Just for demo purposes
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$("#result").html("<div>" +
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"<p></p><strong>Project Name: " + data.name + "</strong></p>" +
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"<p>Project License: " + data.licensing + "</p>" +
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"<p><a href='" + data.repository + "'>Project Repository: " + data.repository + "</a></p>" +
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"<p><a href='" + data.documentation + "'>Project Documentation: " + data.documentation + "</a></p>" +
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"</div>");
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}
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function onError(jqXHR, textStatus, errorThrown) {
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alert('HTTP Status Code: ' + jqXHR.status + ', ' + errorThrown);
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}
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$(document).ready(function () {
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$("#submit").click(function () {
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$.ajax({
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url: "/projects/",
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data: "id=" + $("#projects").val(),
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contentType: 'application/json',
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dataType: 'json',
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success: onSuccess,
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error: onError
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});
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return false;
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});
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});
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</script>
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</%def>
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**What did we just do?**
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#. In the ``head`` section we added jQuery support via the `Google CDN <https://developers.google.com/speed/libraries/devguide>`_
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#. Added JavaScript to make an AJAX call to the server via an HTTP ``GET`` passing in the ``id`` of the project to fetch more information on
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#. Once the ``onSuccess`` event is triggered by the returning data we take that and display it on the web page below the controls
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Adding Additional HTML
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----------------------
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Let's edit the ``index.html`` file next. We will add HTML to support the AJAX interaction between the web page and Pecan. Modify ``index.html`` to look like this:
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.. code-block:: html
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<%inherit file="layout.html" />
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<%def name="title()">
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Welcome to Pecan!
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</%def>
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<header>
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<h1><img src="/images/logo.png"/></h1>
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</header>
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<div id="content">
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<p>Select a project to get details:</p>
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<select id="projects">
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<option value="0">OpenStack</option>
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<option value="1">Pecan</option>
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<option value="2">Stevedore</option>
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</select>
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<button id="submit" type="submit">Submit</button>
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<div id="result"></div>
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</div>
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**What did we just do?**
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#. Added a dropdown control and submit button for the user to interact with. Users can pick an open source project and get more details on it
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Building the Model with JSON Support
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------------------------------------
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The HTML and JavaScript work is now taken care of. At this point we can add a model to our project inside of the ``model`` folder. Create a file in there called ``projects.py`` and add the following to it:
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.. code-block:: python
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class Project(object):
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def __init__(self, name, licensing, repository, documentation):
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self.name = name
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self.licensing = licensing
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self.repository = repository
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self.documentation = documentation
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def __json__(self):
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return dict(
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name=self.name,
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licensing=self.licensing,
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repository=self.repository,
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documentation=self.documentation
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)
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**What did we just do?**
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#. Created a model called ``Project`` that can hold project specific data
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#. Added a ``__json__`` method so an instance of the ``Project class`` can be easily represented as JSON. The controller we will soon build will make use of that JSON capability
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.. note::
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There are other ways to return JSON with Pecan, check out :ref:`jsonify` for more information.
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Working with the Controllers
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----------------------------
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We don't need to do anything major to the ``root.py`` file in the ``controllers`` folder except to add support for a new controller we will call ``ProjectsController``. Modify the ``root.py`` like this:
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.. code-block:: python
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from pecan import expose
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from myajax.controllers.projects import ProjectsController
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class RootController(object):
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projects = ProjectsController()
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@expose(generic=True, template='index.html')
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def index(self):
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return dict()
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**What did we just do?**
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#. Removed some of the initial boilerplate code since we won't be using it
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#. Add support for the upcoming ``ProjectsController``
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The final piece is to add a file called ``projects.py`` to the ``controllers`` folder. This new file will host the ``ProjectsController`` which will listen for incoming AJAX ``GET`` calls (in our case) and return the appropriate JSON response.
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Add the following code to the ``projects.py`` file:
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.. code-block:: python
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from pecan import expose, response
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from pecan.rest import RestController
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from myajax.model.projects import Project
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class ProjectsController(RestController):
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# Note: You would probably store this information in a database
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# This is just for simplicity and demonstration purposes
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def __init__(self):
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self.projects = [
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Project(name='OpenStack',
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licensing='Apache 2',
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repository='http://github.com/openstack',
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documentation='http://docs.openstack.org'),
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Project(name='Pecan',
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licensing='BSD',
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repository='http://github.com/pecan/pecan',
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documentation='https://pecan.readthedocs.io'),
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Project(name='stevedore',
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licensing='Apache 2',
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repository='http://github.com/dreamhost/pecan',
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documentation='http://docs.openstack.org/developer/stevedore/')
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]
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@expose('json', content_type='application/json')
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def get(self, id):
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response.status = 200
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return self.projects[int(id)]
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**What did we just do?**
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#. Created a local class variable called ``projects`` that holds three open source projects and their details. Typically this kind of information would probably reside in a database
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#. Added code for the new controller that will listen on the ``projects`` endpoint and serve back JSON based on the ``id`` passed in from the web page
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Run the application:
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::
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$ pecan serve config.py
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Open a web browser: `http://127.0.0.1:8080/ <http://127.0.0.1:8080/>`_
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There is something else we could add. What if an ``id`` is passed that is not found? A proper ``HTTP 404`` should be sent back. For this we will modify the ``ProjectsController``.
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Change the ``get`` function to look like this:
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.. code-block:: python
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@expose('json', content_type='application/json')
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def get(self, id):
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try:
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response.status = 200
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return self.projects[int(id)]
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except (IndexError, ValueError) as ex:
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abort(404)
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To test this out we need to pass an invalid ``id`` to the ``ProjectsController``. This can be done by going into the ``index.html`` and adding an additional ``option`` tag with an ``id`` value that is outside of 0-2.
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.. code-block:: html
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<p>Select a project to get details:</p>
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<select id="projects">
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<option value="0">OpenStack</option>
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<option value="1">Pecan</option>
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<option value="2">Stevedore</option>
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<option value="3">WSME</option>
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</select>
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You can see that we added ``WSME`` to the list and the value is 3.
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Run the application:
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::
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$ pecan serve config.py
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Open a web browser: `http://127.0.0.1:8080/ <http://127.0.0.1:8080/>`_
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Select ``WSME`` from the list. You should see the error dialog box triggered.
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