Concepts
========

.. _import-vs-export:

Import vs. Export
-----------------

From the framework's perspective, everything is actually an "import"
and never an "export" per se, i.e. data always flows from a source and
to a destination - or in other words, the "local" side always
*imports* from the "host" side.  But see :doc:`exporting` for more
about that.

.. _importer-vs-import-handler:

Importer vs. Import Handler
---------------------------

All import (and export) tasks are accomplished by way of 2 things:

The "importer" is responsible for reading data from one place and
writing it to another place.  But it cannot run itself, it just
contains the e.g. table-specific read/write logic.

The "import handler" is responsible for running one or more importers.
It also is (usually) responsible for "transaction-level" logic, e.g.
connecting to a database, and ultimately committing that transaction.
It usually has no table-specific logic, as that is the importer's job.

For instance you might want to import all customers and products from
your POS into Rattail; this would require something like:

 * import handler for POS -> Rattail
 * importer for Customer data
 * importer for Product data