Example of how to add a custom preview on CKAN 2.2 that embeds a URL based on a resource field

ckanext-example_ckanext_example_templates_package_snippets_resource_form.html

<form id="resource-edit" class="dataset-form dataset-resource-form form-horizontal" method="post" action="{{ action }}" data-module="basic-form resource-form" enctype="multipart/form-data">

...

      {{ form.input('url_viz', id='field-url_viz', label=_('URL Viz'), value=data.url_viz, error=errors.url_viz, classes=[]) }}

...

embeded_viz.html

{% extends 'dataviewer/base.html' %}

{% block page %}
  <div>
    <pre data-module="textpreview">
      <div class="loading">

      Add an iframe here pointing to {{ c.resource.url_viz }}

      </div>
    </pre>
  </div>

{% endblock %}

plugin.py

import ckan.plugins as plugins
import ckan.plugins.toolkit as toolkit


class PluginClass(plugins.SingletonPlugin, toolkit.DefaultDatasetForm):
    plugins.implements(plugins.IConfigurer)
    plugins.implements(plugins.IDatasetForm)
    plugins.implements(plugins.IResourcePreview)

    # IConfigurer

    def update_config(self, config):
        # Register this extension templates directory

        toolkit.add_template_directory(config, 'templates')

    # IDatasetForm

        # This will register our custom "url_viz" field in the resources schema

    def is_fallback(self):
        return True

    def package_types(self):
        return ('dataset',)

    def _customize_package_schema(self, schema):

        schema['resources']['url_viz'] = [toolkit.get_validator('not_missing')]

    def create_package_schema(self):
        schema = super(PluginClass, self).create_package_schema()
        self._customize_package_schema(schema)
        return schema

    def update_package_schema(self):
        schema = super(PluginClass, self).update_package_schema()
        self._customize_package_schema(schema)
        return schema

    def show_package_schema(self):
        schema = super(PluginClass, self).show_package_schema()
        self._customize_package_schema(schema)
        return schema

    # IResourcePreview

        # This configures a custom preview that looks for the "url_viz" field
        # and shows an iframe to embed it

    def can_preview(self, data_dict):

        # Need to do this stuff because custom fields are not available
        # data_dict['resource']

        can_preview = False
        if not data_dict.get('package'):
            return can_preview
        for resource in data_dict['package'].get('resources', []):
            if resource['id'] == data_dict['resource']['id']:
                can_preview = 'url_viz' in resource

        return can_preview

    def setup_template_variables(self, context, data_dict):
        if not data_dict.get('package'):
            return

        # Need to do this stuff because custom fields are not available
        # data_dict['resource']

        for resource in data_dict['package'].get('resources', []):
            if resource['id'] == data_dict['resource']['id']:
                toolkit.c.resource['url_viz'] = resource['url_viz']

    def preview_template(self, context, data_dict):

        return 'embeded_viz.html'