Add cache warmup endpoint (#1063)

* Refactor permissions in the views.py.

* Add get_viz to the slice.

* Add warm up cache endpoint.

* Resolve comments.

caravel/models.py

@@ -43,6 +43,8 @@
 from sqlalchemy.sql.expression import TextAsFrom
 from sqlalchemy_utils import EncryptedType
 
+from werkzeug.datastructures import ImmutableMultiDict
+
 import caravel
 from caravel import app, db, get_session, utils, sm
 from caravel.viz import viz_types
@@ -250,6 +252,30 @@ def slice_link(self):
         return '<a href="{url}">{obj.slice_name}</a>'.format(
             url=url, obj=self)
 
+    def get_viz(self, url_params_multidict=None):
+        """Creates :py:class:viz.BaseViz object from the url_params_multidict.
+
+        :param werkzeug.datastructures.MultiDict url_params_multidict:
+            Contains the visualization params, they override the self.params
+            stored in the database
+        :return: object of the 'viz_type' type that is taken from the
+            url_params_multidict or self.params.
+        :rtype: :py:class:viz.BaseViz
+        """
+        slice_params = json.loads(self.params)  # {}
+        slice_params['slice_id'] = self.id
+        slice_params['json'] = "false"
+        slice_params['slice_name'] = self.slice_name
+        slice_params['viz_type'] = self.viz_type if self.viz_type else "table"
+        if url_params_multidict:
+            slice_params.update(url_params_multidict)
+        immutable_slice_params = ImmutableMultiDict(slice_params)
+        return viz_types[immutable_slice_params.get('viz_type')](
+            self.datasource,
+            form_data=immutable_slice_params,
+            slice_=self
+        )
+
 
 def set_perm(mapper, connection, target):  # noqa
     if target.table_id: