Add a workaround for table referencing another from different DAG

This replaces node's parent to link to root, instead of failing to lookup table from another DAG
Also references issue created on Github

dashboard/model/tables_data.py

@@ -1,5 +1,6 @@
 import csv
 from concurrent.futures import ThreadPoolExecutor
+from typing import Dict
 
 from dashboard.models import Period, Table
 from dashboard.utils import clean_dag_id, handle_resource, simple_state
@@ -43,7 +44,6 @@ class DagTableProgress:
 
 class TableDataProvider:
 
-
     @staticmethod
     def _format_table_id(table):
         id = table['db'] + '.' + table['name']
@@ -75,8 +75,8 @@ def get_tables(self):
     def history(self, table):
         return self.__get_detailed_view_data(self.tables[table], DETAILED_CHART_DAYS_NUM)
 
-    def get_tables_by_dag(self, dag_name):
-        return [table for table in self.tables.values() if table.dag_id == dag_name]
+    def get_tables_by_dag(self, dag_name) -> Dict[str, Table]:
+        return {id: table for id, table in self.tables.items() if table.dag_id == dag_name}
 
     def get_tables_graph(self, dag_id, execution_date):
         name_without_version = clean_dag_id(dag_id)
@@ -89,7 +89,7 @@ def get_tables_graph(self, dag_id, execution_date):
                           state=self.airflow.get_dag_state(dag_id, execution_date))
 
         # tables
-        for table in dag_tables:
+        for table in dag_tables.values():
             yield GraphVertex(
                 id=table.id,
                 name=table.name + (' ({})'.format(table.period.name) if table.period else ''),
@@ -98,7 +98,9 @@ def get_tables_graph(self, dag_id, execution_date):
                     dag_progress[table.task_id].end_date,
                     dag_progress[table.task_id].duration
                 ),
-                parent=table.get_parent()
+                # workaround for table.uses not being able to reference table managed by other DAG
+                # see https://github.com/Wikia/discreETLy/issues/22
+                parent='main' if table.uses is None or table.uses not in dag_tables.keys() else table.uses
             )
 
     @handle_resource('influx')