.. _client_label:

Using the Client
****************
Users will interact with the database by using the :class:`happi.Client`, this
will handle the authentication, and methods for adding, editing and removing
devices.

Happi is incredibly flexible, allowing us to put arbitrary key-value pair
information into the databse. While this will make adding functionality easy in
the future, it also means that any rules on the structure of the data we allow
will need to be performed by the :class:`.happi.Client` itself. To make this
intuitive, the client deals primarily with objects we will call Device
Containers, see :ref:`device_label` in order to see more about how the devices
are created. However the basic use cases for the client can be demonstrated
without much knowledge of how the :class:`.Device` container works.

.. _entry_code:

Creating a New Entry
^^^^^^^^^^^^^^^^^^^^
A new device must be a subclass of the basic container :class:`.Device`.
While you are free to use the initialized object whereever you see fit, the client
has a hook to create new devices. 

Before we can create our first client, we need to create a backend for our device
information to be stored.

.. ipython:: python

    from happi.backends.json_db import JSONBackend

    db = JSONBackend(path='doc_test.json', initialize=True)

If you are connecting to an existing database you can pass the information
directly into the ``Client`` itself at `__init__``. See :ref:`db_choice`
about how to configure your default backend choice

.. ipython:: python

    from happi import Client, Device

    client = Client(path='doc_test.json')

    device = client.create_device("Device", name='my_device',prefix='PV:BASE', beamline='XRT', z=345.5)
    
    device.save()

Alternatively, you can create the device separately and add the device
explicitly using :meth:`.Device.save`

.. ipython:: python

    device = Device(name='my_device2',prefix='PV:BASE2', beamline='MFX', z=355.5)
   
    client.add_device(device)

The main advantage of the first method is that all of the container classes are
already stored in the :attr:`.Client.device_types` dictionary so they can be
easily accessed with a string. Keep in mind, that either way, all of the
mandatory information needs to be given to the device before it can be loaded
into the database. For more information on device creation see
:ref:`device_label`.
    
Searching the Database
^^^^^^^^^^^^^^^^^^^^^^
There are two ways to load information from the database
:meth:`.Client.find_device` and :meth:`.Client.search`. The former should only
be used to load one device at at a time. Both accept criteria in the from of
keyword-value pairs to find the device or device/s you desire. Here are some
example searches to demonstrate the power of the Happi Client

First, lets look for all the devices of type generic ``Device``, as first their
corresponding objects or as a dictionary

.. ipython:: python
    
    client.search(type='Device')

    client.search(type='Device', as_dict=True)


There are also some more advance methods to search specific areas of the
beamline


.. ipython:: python
    
    client.search(type='Device', beamline='MFX')
   
    client.search(type='Device', start=314.4, end=348.6)

You can also explicitly load a single device. The advantage of this method is
you won't have to parse a list of returned devices. If nothing meets your given
criteria, an ``SearchError`` will be raised 

.. ipython:: python

   device =  client.find_device(prefix='PV:BASE2')

   print(device.prefix, device.name)

   try:
       client.find_device(name='non-existant')
   except Exception as exc:
       print(exc)


Editing Device Information
^^^^^^^^^^^^^^^^^^^^^^^^^^
The workflow for editing a device looks very similar to the code within
:ref:`entry_code`, but instead of instantiating the device you use either
:meth:`.Client.find_device` or :meth:`.Client.search` to grab an existing device from
the dataprefix. When the device is retreived this way the class method
:meth:`.Device.save` is overwritten, simply call this when you are done editing
the Device information.

.. ipython:: python

    my_motor = client.find_device(prefix='PV:BASE')
    
    my_motor.z = 425.4
    
    my_motor.save()

.. note::

    Because the database uses the ``prefix`` key as a device's identification you
    can not edit this information in the same way. Instead you must explicitly
    remove the device and then use :meth:`.Client.add_device` to create a new
    entry. 
    
Finally, lets clean up our example objects by using
:meth:`.Client.remove_device` to clean them from the database

.. ipython:: python

    device_1 = client.find_device(name='my_device')
    
    device_2 = client.find_device(name='my_device2')

    for device in (device_1, device_2):
        client.remove_device(device)

.. _db_choice:

Selecting a Backend
^^^^^^^^^^^^^^^^^^^
Happi supports both JSON and MongoDB backends. You can always import your
chosen backend directly, but in order to save time you can create an
environment variable ``HAPPI_BACKEND`` and set this to ``"mongodb"``. This well
tell the library to assume you want to use the :class:`.MongoBackend`.
Otherwise, the library uses the :class:`.JSONBackend`.