Imports the dashboard from the object to the database.

         Once dashboard is imported, json_metadata field is extended and stores
         remote_id and import_time. It helps to decide if the dashboard has to
         be overridden or just copies over. Slices that belong to this
         dashboard will be wired to existing tables. This function can be used
         to import/export dashboards between multiple superset instances.
         Audit metadata isn't copied over.

def import_obj(cls, dashboard_to_import, import_time=None):
        """Imports the dashboard from the object to the database.

         Once dashboard is imported, json_metadata field is extended and stores
         remote_id and import_time. It helps to decide if the dashboard has to
         be overridden or just copies over. Slices that belong to this
         dashboard will be wired to existing tables. This function can be used
         to import/export dashboards between multiple superset instances.
         Audit metadata isn't copied over.
        """
        def alter_positions(dashboard, old_to_new_slc_id_dict):
            """ Updates slice_ids in the position json.

            Sample position_json data:
            {
                "DASHBOARD_VERSION_KEY": "v2",
                "DASHBOARD_ROOT_ID": {
                    "type": "DASHBOARD_ROOT_TYPE",
                    "id": "DASHBOARD_ROOT_ID",
                    "children": ["DASHBOARD_GRID_ID"]
                },
                "DASHBOARD_GRID_ID": {
                    "type": "DASHBOARD_GRID_TYPE",
                    "id": "DASHBOARD_GRID_ID",
                    "children": ["DASHBOARD_CHART_TYPE-2"]
                },
                "DASHBOARD_CHART_TYPE-2": {
                    "type": "DASHBOARD_CHART_TYPE",
                    "id": "DASHBOARD_CHART_TYPE-2",
                    "children": [],
                    "meta": {
                        "width": 4,
                        "height": 50,
                        "chartId": 118
                    }
                },
            }
            """
            position_data = json.loads(dashboard.position_json)
            position_json = position_data.values()
            for value in position_json:
                if (isinstance(value, dict) and value.get('meta') and
                        value.get('meta').get('chartId')):
                    old_slice_id = value.get('meta').get('chartId')

                    if old_slice_id in old_to_new_slc_id_dict:
                        value['meta']['chartId'] = (
                            old_to_new_slc_id_dict[old_slice_id]
                        )
            dashboard.position_json = json.dumps(position_data)

        logging.info('Started import of the dashboard: {}'
                     .format(dashboard_to_import.to_json()))
        session = db.session
        logging.info('Dashboard has {} slices'
                     .format(len(dashboard_to_import.slices)))
        # copy slices object as Slice.import_slice will mutate the slice
        # and will remove the existing dashboard - slice association
        slices = copy(dashboard_to_import.slices)
        old_to_new_slc_id_dict = {}
        new_filter_immune_slices = []
        new_timed_refresh_immune_slices = []
        new_expanded_slices = {}
        i_params_dict = dashboard_to_import.params_dict
        remote_id_slice_map = {
            slc.params_dict['remote_id']: slc
            for slc in session.query(Slice).all()
            if 'remote_id' in slc.params_dict
        }
        for slc in slices:
            logging.info('Importing slice {} from the dashboard: {}'.format(
                slc.to_json(), dashboard_to_import.dashboard_title))
            remote_slc = remote_id_slice_map.get(slc.id)
            new_slc_id = Slice.import_obj(slc, remote_slc, import_time=import_time)
            old_to_new_slc_id_dict[slc.id] = new_slc_id
            # update json metadata that deals with slice ids
            new_slc_id_str = '{}'.format(new_slc_id)
            old_slc_id_str = '{}'.format(slc.id)
            if ('filter_immune_slices' in i_params_dict and
                    old_slc_id_str in i_params_dict['filter_immune_slices']):
                new_filter_immune_slices.append(new_slc_id_str)
            if ('timed_refresh_immune_slices' in i_params_dict and
                    old_slc_id_str in
                    i_params_dict['timed_refresh_immune_slices']):
                new_timed_refresh_immune_slices.append(new_slc_id_str)
            if ('expanded_slices' in i_params_dict and
                    old_slc_id_str in i_params_dict['expanded_slices']):
                new_expanded_slices[new_slc_id_str] = (
                    i_params_dict['expanded_slices'][old_slc_id_str])

        # override the dashboard
        existing_dashboard = None
        for dash in session.query(Dashboard).all():
            if ('remote_id' in dash.params_dict and
                    dash.params_dict['remote_id'] ==
                    dashboard_to_import.id):
                existing_dashboard = dash

        dashboard_to_import.id = None
        alter_positions(dashboard_to_import, old_to_new_slc_id_dict)
        dashboard_to_import.alter_params(import_time=import_time)
        if new_expanded_slices:
            dashboard_to_import.alter_params(
                expanded_slices=new_expanded_slices)
        if new_filter_immune_slices:
            dashboard_to_import.alter_params(
                filter_immune_slices=new_filter_immune_slices)
        if new_timed_refresh_immune_slices:
            dashboard_to_import.alter_params(
                timed_refresh_immune_slices=new_timed_refresh_immune_slices)

        new_slices = session.query(Slice).filter(
            Slice.id.in_(old_to_new_slc_id_dict.values())).all()

        if existing_dashboard:
            existing_dashboard.override(dashboard_to_import)
            existing_dashboard.slices = new_slices
            session.flush()
            return existing_dashboard.id
        else:
            # session.add(dashboard_to_import) causes sqlachemy failures
            # related to the attached users / slices. Creating new object
            # allows to avoid conflicts in the sql alchemy state.
            copied_dash = dashboard_to_import.copy()
            copied_dash.slices = new_slices
            session.add(copied_dash)
            session.flush()
            return copied_dash.id