Adding features

We'll next implement the ability to add a new feature. To do this, we'll put an Add Feature button onto the "Edit Shapefile" view. Clicking on this button will call the "Edit Feature" URL, but without a feature ID. We'll then modify the "Edit Feature" view so that if no feature ID is given, a new Feature object is created.

Open the shapefiles application's views.py module, find the edit_shapefile() function, and add the following highlighted lines to this function:

def edit_shapefile(request, shapefile_id):
    try:
        shapefile = Shapefile.objects.get(id=shapefile_id)
    except Shapefile.DoesNotExist:
        raise Http404

    tms_url = "http://"+request.get_host()+"/tms/"
    find_feature_url = "http://" + request.get_host() \
                     + "/editor/find_feature"
    add_feature_url = "http://" + request.get_host() \
                    + "/edit_feature/" + str(shapefile_id)
 
    return render(request, "select_feature.html",
                  {'shapefile'      : shapefile,
                   'find_feature_url' : find_feature_url,
                   'add_feature_url' : add_feature_url,
                   'tms_url'        : tms_url})

Then, edit the select_feature.html template and add the following highlighted lines to the body of this template:

<body onload="init()">
  <h1>Edit Shapefile</h1>
  <b>Please choose a feature to edit</b>
  <br/>
  <div id="map" class="map"></div>
  <br/>
  <div style="margin-left:20px">
    <button type="button"
     onClick='window.location="{{ add_feature_url }}";'>
      Add Feature
    </button>
    <button type="button"
      onClick='window.location="/";'>
      Cancel
    </button>
  </div>
</body>

This will place an Add Feature button onto the "Select Feature" page. Clicking on that button will call the http://127.0.0.1:8000/edit_feature/N URL (where N is the record ID of the current shapefile). As you can see, this URL supplies the ID of the desired shapefile but not the ID of the feature to edit. This is because we're adding a new feature rather than editing an existing one.

We next need to add a URL pattern to support this URL. Open the urls.py module and add the following entry to the URL pattern list:

  url(r'^edit_feature/(?P<shapefile_id>\d+)$',
      shapeEditor.shapefiles.views.edit_feature),

Then, go back to views.py and change the function definition for the edit_feature() function to look like this:

def edit_feature(request, shapefile_id, feature_id=None):

Notice that the feature_id parameter is now optional. Now, find the following block of code:

  try:
    feature = Feature.objects.get(id=feature_id)
  except Feature.DoesNotExist:
    return HttpResponseNotFound()

You need to replace this block with the following:

  if feature_id == None:
    feature = Feature(shapefile=shapefile)
  else:
    try:
      feature = Feature.objects.get(id=feature_id)
    except Feature.DoesNotExist:
      return HttpResponseNotFound()

This will create a new Feature object if the feature_id value is not specified, but it will still fail if an invalid feature ID is specified.

With these changes, you should be able to add a new feature to the shapefile. Go ahead and try it out: run the Django web server if it's not already running, and click on the Edit hyperlink for your imported shapefile. Then, click on the Add New Feature hyperlink, and try creating a new feature. The new feature should appear within the "Select Feature" view:

Table of Contents for Python Geospatial Development - Third Edition

Adding features

Table of Contents for
Python Geospatial Development - Third Edition