Implement PUT method for empty JSON list

To clear/empty a data-set, you PUT an empty JSON list to the data
endpoint (ie /data/my-data-group/my-data-type).

We currently only allow an empty list - in the future we could extend to
allow setting the entire contents of the data set.

https://www.pivotaltracker.com/story/show/69622004

[Delivers #69622004]

backdrop/core/data_set.py

@@ -61,6 +61,10 @@ def query(self, query):
 
         return result
 
+    def empty(self):
+        collection = self.db.get_collection(self.config.name)
+        collection.remove({})
+
     def _add_id(self, datum):
         self._validate_presence_of_auto_id_keys(datum)
         return dict(datum.items() + [("_id", self._generate_id(datum))])

backdrop/core/database.py

@@ -119,6 +119,9 @@ def group(self, keys, query, collect_fields):
             reduce=self._build_reducer_function(collect_fields)
         )
 
+    def remove(self, *args, **kwargs):
+        return self._collection.remove(*args, **kwargs)
+
     def _build_collector_code(self, collect_fields):
         template = "if (current['{c}'] !== undefined) " \
                    "{{ previous['{c}'].push(current['{c}']); }}"

backdrop/write/api.py

@@ -90,6 +90,34 @@ def write_by_group(data_group, data_type):
         abort(400, repr(e))
 
 
+@app.route('/data/<data_group>/<data_type>', methods=['PUT'])
+@cache_control.nocache
+def put_by_group_and_type(data_group, data_type):
+    """
+    Put by group/type
+    e.g. PUT https://BACKDROP/data/gcloud/sales
+    Note: At the moment this is just being used to empty data-sets.
+          Trying to PUT a non empty list of records will result in a
+          PutNonEmptyNotImplementedError exception.
+    """
+    data_set_config = data_set_repository.get_data_set_for_query(
+        data_group,
+        data_type)
+
+    _validate_config(data_set_config)
+    _validate_auth(data_set_config)
+
+    try:
+        data = listify_json(request.json)
+        if len(data) > 0:
+            abort(400, 'Not implemented: you can only pass an empty JSON list')
+
+        return _empty_data_set(data_set_config)
+
+    except (ParseError, ValidationError) as e:
+        abort(400, repr(e))
+
+
 @app.route('/<data_set:data_set_name>', methods=['POST'])
 @cache_control.nocache
 def post_to_data_set(data_set_name):
@@ -198,6 +226,14 @@ def _append_to_data_set(data_set_config, data, ok_message=None):
         return jsonify(status='ok')
 
 
+def _empty_data_set(data_set_config):
+    data_set = DataSet(db, data_set_config)
+    data_set.empty()
+    return jsonify(
+        status='ok',
+        message='{} now contains 0 records'.format(data_set_config.name))
+
+
 def listify_json(data):
     if data is None:
         raise ValidationError("Request must be JSON")

features/support/http_test_client.py

@@ -15,17 +15,30 @@ def get(self, url, headers=None):
         return HTTPTestResponse(response)
 
     def post(self, url, **message):
+        return self.post_or_put('POST', url, **message)
+
+    def put(self, url, **message):
+        return self.post_or_put('PUT', url, **message)
+
+    def post_or_put(self, method, url, **message):
+        assert method in ('POST', 'PUT'), 'Only support POST, PUT'
+        http_function = {
+            'POST': requests.post,
+            'PUT': requests.put
+        }[method]
+
         headers = dict(message.get("headers", []))
+
         if "data" in message:
             headers.update({"Content-type": message['content_type']})
-            response = requests.post(
+            response = http_function(
                 self._write_api.url(url),
                 data=message['data'],
                 headers=headers,
                 timeout=60,
             )
         elif "files" in message:
-            response = requests.post(
+            response = http_function(
                 self._write_api.url(url),
                 files=message['files'],
                 headers=headers,