Creating an app
===============

The Django web site has a very good
`tutorial <https://docs.djangoproject.com/en/dev/intro/tutorial01/>`_ to
get you familiar with the Django framework. The more you know about
Django, the easier you will find it working with the OmeroWeb framework.
One major feature of Django that we do not use in OmeroWeb is the Django
database mapping, since all data comes from the OMERO server and is
saved back there. You will notice that the models.py files in each app
are empty.

.. note:: Since OMERO 5.0, the web framework uses Django 1.6 instead of Django 1.3.
    One important change is the syntax of the
    `url template tag <https://docs.djangoproject.com/en/dev/ref/templates/builtins/#std:templatetag-url>`_,
    which now requires quotes, and will need to be updated for OMERO 4.4 web apps moving to OMERO 5.0.

Getting set up
--------------

You will need to have an OMERO server running that you can connect to.
This will typically be on your own machine, although it does not
necessarily have to be. If you want to connect to another server (not
localhost) you can edit the server list as described on the OMERO.web 
deployment page (see :doc:`Unix </sysadmins/unix/install-web>` or 
:doc:`Windows </sysadmins/windows/install-web>` version) and choose that 
server when you log in. That page also describes how to set debug to 'True' 
which is important when developing with OMERO.web and you should also be using 
the Django 'development' server.

::

    $ bin/omero web start
    Starting django development webserver... 
    Validating models...

    0 errors found
    December 09, 2013 - 14:34:10
    Django version 1.6, using settings 'omeroweb.settings'
    Starting development server at http://127.0.0.1:4080/
    Quit the server with CONTROL-C.

.. note:: Port number is 4080

You should make sure that you can access the webclient and webadmin on
your local machine before starting to develop your own code. Be sure to
use the correct port number, E.g:

-  ` http://localhost:4080/webclient/ <http://localhost:4080/webclient/>`_

When you edit and save your app, Django will
automatically detect this and you only need to refresh your browser
to see the changes. You can see this in the :snapshot:`OMERO.web intro
movie <movies/omero-4-3/mov/OmeroWebIntro-4.3.mov>`.

If you want to run OMERO.web from source code, see :doc:`/developers/Web/EditingOmeroWeb`.

You can place your app anywhere on your :envvar:`PYTHONPATH`,
as long as it can be imported by OMERO.web.

.. note::

   OMERO 5 uses Django 1.6 which has a different project layout from OMERO 4.4. 
   If you are upgrading your app from 4.4.x you may need to update some import
   statements. E.g. ``from omeroweb import webgateway`` will become
   ``import webgateway``.

Creating an app
---------------

We suggest you use github (as we do) since it is much easier for us to
help you with any problems you have if we can see your code. The steps below
describe how to create a stand-alone git repository for your app, similar to 
`webtagging <https://github.com/dpwrussell/webtagging>`_.
If you do not want to use github, simply ignore the github steps below.

The steps below describe setting up a new app. You should choose an
appropriate name for your app and use it in place of <your-app> in the
examples below:

Create and checkout a new github repository OR manually create a new directory
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

-  Login to your github account homepage (E.g.
   `<https://github.com/>`_\ <your-name>/) and click
   "New repository"
-  Enter the name of <your-app>, add description and choose to add
   README.

-  Checkout your new repository (into a new directory)

   ::

       $ git clone git@github.com:<your-name>/<your-app>.git


-  OR: If you haven't used git to create your app directory above, then

   ::

        $ mkdir <your-app>

Add your app location to your PYTHONPATH
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If your app is not in a directory that is already on your :envvar:`PYTHONPATH`
then you need to add it:

::

    $ export PYTHONPATH=$PYTHONPATH:/path/to/your-app

Add the essential files to your app
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

-  Create an empty file ``<your-app>/__init__.py`` (NB: both double
   underscores)
-  Create urls.py

   ::

       from django.conf.urls.defaults import *
       from omeroweb.<your-app> import views

       urlpatterns = patterns('django.views.generic.simple',

            # index 'home page' of the <your-app> app
            url( r'^$', views.index, name='<your-app>_index' ),

        )

-  Create views.py

   ::

        from django.http import HttpResponse

        def index(request):
            """
            Just a place-holder while we get started
            """
            return HttpResponse("Welcome to your app home-page!")

Add your app to OMERO.web
~~~~~~~~~~~~~~~~~~~~~~~~~

This will add your app to the INSTALLED\_APPS, so that URLs are
registered etc.

::

    $ bin/omero config set omero.web.apps '["<your-app>"]'

.. note::

    For releases before 4.4, you need to 'register' your app with Django
    manually by adding it to the INSTALLED\_APPS list in
    omeroweb/settings.py following the pattern of existing apps there. You
    also need to edit omeroweb/urls.py to add your app's urls.py file to the
    list of "urlpatterns". Again, you should be able to follow the existing
    examples there. You can also specify at this point the URL under which
    your app will be found.

Now you can view the home-page we created above (NB: you will need to
restart the OMERO.web server for the config settings to take effect)

::

     $ bin/omero web stop
     $ bin/omero web start

Go to ` http://localhost:4080/ <http://localhost:4080/>`_\ <your-app>/
OR ` http://localhost:8000/ <http://localhost:8000/>`_\ <your-app>/
Should see 'Welcome'

Commit your code and push to github
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

::

    $ git status (see new files, plus .pyc files)
    $ echo "*.pyc" > .gitignore         # ignore .pyc files
    $ echo ".gitignore" >> .gitignore   # ALSO ignore .gitignore

    $ git add ./
    $ git commit -m "Initial commit of bare-bones OMERO.web app"
    $ git push origin master

Connect to OMERO: example
~~~~~~~~~~~~~~~~~~~~~~~~~

We have got our new app working, but it is not connecting to OMERO yet.
Let us create a simple "stack preview" for an Image with multiple
Z-sections. We are going to display the image name and 5 planes evenly
spaced across the Z-stack. You should be able to add the appropriate
code to urls.py, views.py that you created above, and add a template
under /omeroweb/<your-app>/templates/<your-app>/ 

.. note::

   note that /<your-app>/ appears twice in that path (need an extra folder 
   under templates). This example can be found in webtest.

-  **urls.py**

   ::

       url( r'^stack_preview/(?P<imageId>[0-9]+)/$', views.stack_preview, 
            name="<your-app>_stack_preview" ),

-  **views.py** Here we are using the @login\_required decorator to
   retrieve a connection to OMERO from the session key in the HTTP
   request (or provide a login page and redirect here). 'conn' is passed
   to the method arguments. NB: Note a couple of new imports to add at
   the top of your page.

   ::

       from omeroweb.webclient.decorators import login_required
       from django.shortcuts import render_to_response


       @login_required()
       def stack_preview (request, imageId, conn=None, **kwargs):
           """ Shows a subset of Z-planes for an image """
           image = conn.getObject("Image", imageId)       # Get Image from OMERO
           image_name = image.getName()
           sizeZ = image.getSizeZ()                        # get the Z size
           # 5 Z-planes
           z_indexes = [0, int(sizeZ*0.25), 
                    int(sizeZ*0.5), int(sizeZ*0.75), sizeZ-1]
           return render_to_response('webtest/stack_preview.html',
                {'imageId':imageId, 
                'image_name':image_name, 
                'z_indexes':z_indexes})

-  **<your-app>/templates/<your-app>/stack\_preview.html**

   ::

       <html>
       <head>
            <title>Stack Preview</title>
       </head>
       <body>
            <h1>{{ image_name }}</h1>

            {% for z in z_indexes %}
                <img src="{% url 'webgateway.views.render_image' imageId z 0 %}"
                    style="max-width: 200px; max-height:200px"/>
            {% endfor %}
       </body>
       </html>


Viewing the page at http://localhost:4080/<your-app>/stack_preview/<image-id>/ 
should give you the image name and 5 planes from the Z stack. You will notice 
that we are using webgateway to handle the image rendering using a URL 
auto-generated by Django - see :doc:`/developers/Web/WebGateway`.

Resources for writing your own code
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The webtest app has a number of examples. If you go to the webtest
homepage E.g. `<http://localhost:8000/webtest>`_ you will
see an introduction to some of them. This page tries to find random
image and dataset from your OMERO server to use in the webtest examples.

Extending templates
~~~~~~~~~~~~~~~~~~~

We provide several HTML templates in
webgateway/templates/webgateway/base. This is a nice way of giving users
the feeling that they have not left the webclient, if you are providing
additional functionality for webclient users. You may choose not to use
this if you are building a 'stand-alone' web application. In either
case, it is good practice to create your own templates with common
components (links, logout etc), so you can make changes to all your
pages at once. See :doc:`/developers/Web/WritingTemplates` for more info.

App settings
~~~~~~~~~~~~

You can add settings to your app that allow configuration via the command line
in the same way as for the base OMERO.web in omeroweb/settings.py.
The list of CUSTOM_SETTINGS_MAPPINGS in omeroweb/settings.py code is a good
source for examples of the different data types and parsers you can use.

For example, if you want to create a user-defined setting yourapp.foo,
that contains a dictionary of key-value pairs, you can add to
CUSTOM_SETTINGS_MAPPINGS in yourapp/settings.py:

::

    import json
    CUSTOM_SETTINGS_MAPPINGS = {
        "omero.web.yourapp.foo": ["FOO", '{"key": "val"}', json.loads]
    }

From somewhere else in your app, you can then access the settings:

::

    from yourapp import settings

    print settings.FOO

Users can then configure this on the command line as follows:

::

    $ bin/omero config set omero.web.yourapp.foo '{"userkey": "userval"}'


OMERO.web top links
~~~~~~~~~~~~~~~~~~~

You can configure settings 'top_links' to add a link to the list of links at the
top of the webclient main pages.

-  **Name your url in urls.py** (optional). Preferably we use url names to refer to urls.
   For example, the homepage of your app might be named like this in urls.py.

   ::

       url( r'^$', views.index, name='webmobile_index' ),


-  **Update configuration** Use the OMERO command line interface to add the link or links to the appropriate list.
   NB: Since there is not currently an option to **add** to web settings lists, you will need to include
   the full list of links when you configure the list.

To add a single link, using the format ["Label", "URL_name"], you can follow this example:

::

    $ bin/omero config set omero.web.ui.top_links '[["Mobile", "webmobile_index"]]'

Multiple links can be added in the same way. 
You can also create **external** links by specifying the full URL instead of the "URL_name". For example:

::

    $ bin/omero config set omero.web.ui.top_links '[["Mobile", "webmobile_index"], ["OME", "https://www.openmicroscopy.org"]]'


OMERO.web plugins (OMERO 4.4)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you want to display content from your app within the webclient UI, please see :doc:`/developers/Web/WebclientPlugin`.