==================================
Izenda Database Behaviors
==================================


Soft Delete
-----------

Instead of physically removing rows, Izenda will set the Deleted flag on
them to preserve historical data. Therefore, normal-case queries should
always include a ``Deleted = 0`` condition.

Report/Dashboard-specific Data
------------------------------

Report Relationship Data
~~~~~~~~~~~~~~~~~~~~~~~~

Each report uses its own set of relationships. Report creators are free
to modify or remove the default relationships suggested from Data Model
or create new ones. Therefore, IzendaRelationship table stores both Data
Model relationships (without a ReportId) and Report-specific
relationships (with a value in ReportId). Report-specific relationships
will also be deleted along with the report.

Example:

   .. _Data_Model_and_Report_Relationships:

   .. figure:: /_static/images/Data_Model_and_Report_Relationships.png

      Data Model and Report Relationships.png


* First row is a Data Model relationship.
* Second row is a Report relationship with value in ReportId, and copied from the Data Model relationship above.

Dashboard Filter Data
~~~~~~~~~~~~~~~~~~~~~

Dashboard part can use a different filter value than the specified value
in the included report part. Therefore, dashboard part filter data is
stored in the separate table IzendaDashboardPartFilterField, with the
default values copied from report filter data in
Izenda(ReportPart)FilterField.

Subscription Filter Data
~~~~~~~~~~~~~~~~~~~~~~~~

Specific subscriptions can also choose to use a different filter value
than the one in report/dashboard. Therefore, subscription filter data is
also stored in a separate table IzendaSubscriptionFilterField.

History Tables
--------------

History tables are used to keep previous versions of the data in a
separate place, for specific Izenda features:

-  IzendaReportHistory

       to display in :ref:`View_Report_History` in Report List.

-  IzendaPasswordHistory

       to validate against new passwords following :doc:`../ui/doc_configuration_security_policies`.

.. note::

   Normal tables only retain deleted data for a short time before archiving, and do not keep updated data. Hence, there should be no attempt to read history information from them.