Facet adjustments.

- Only update eurovoc_category_label facet if not already present in
  facet dict.
- Add further information about facet search to readme.

README.rst

@@ -66,9 +66,6 @@ do::
 Configuration
 -------------
 
-Adding templates, and Eurovoc category field to the dataset schema
-++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
-
 The Eurovoc plugin doesn't automatically change CKAN templates or add a Eurovoc
 category field to your dataset schema.
 
@@ -124,6 +121,17 @@ Note: Changing the value of ``category_field_name`` will not migrate previous
 values assigned to the old field name.
 
 
+Search facet
+++++++++++++
+
+The Eurovoc plugin will add a faceted search option to dataset, group and
+organization search page.
+
+You can make adjustments to the Eurovoc facet in your own extension by
+updating the ``eurovoc_category_label`` entry in the facet dictionary using
+the appropriate ``IFacets`` interface methods.
+
+
 -----------------
 Running the Tests
 -----------------

ckanext/eurovoc/plugin.py

@@ -94,9 +94,11 @@ def organization_facets(self, facets_dict, organization_type, package_type):
         return facets_dict
 
     def _update_facets(self, facets_dict):
-        facets_dict.update({
-            'eurovoc_category_label': plugins.toolkit._('Eurovoc Categories')
-        })
+        '''Add `eurovoc_category_label` to facets if not already present.'''
+        if 'eurovoc_category_label' not in facets_dict:
+            facets_dict.update({
+                'eurovoc_category_label': plugins.toolkit._('Eurovoc Categories')
+            })
 
     # IPackageController