Using the Client

Users will interact with the database by using the 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 happi.Client itself. To make this intuitive, the client deals primarily with objects we will call Containers, see Containers in order to see more about how they are created.

Creating a New Entry

A new device must be a subclass of the basic container 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.

In [1]: from happi.backends.json_db import JSONBackend

In [2]: 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 Selecting a Backend about how to configure your default backend choice

In [3]: from happi import Client, Device

In [4]: client = Client(path='doc_test.json')

In [5]: device = client.create_device("Device", name='my_device',prefix='PV:BASE', beamline='XRT', z=345.5, location_group="Loc1", functional_group="Func1", device_class='types.SimpleNamespace', args=[])

In [6]:

Alternatively, you can create the device separately and add the device explicitly using

In [7]: device = Device(name='my_device2',prefix='PV:BASE2', beamline='MFX', z=355.5, location_group="Loc2", functional_group="Func2")

In [8]: client.add_device(device)
Out[8]: 'my_device2'

The main advantage of the first method is that all of the container classes are already stored in the 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.

Searching the Database

There are two ways to load information from the database Client.find_device() and 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:

In [9]: results ='Device')

This returns a list of zero or more SearchResult instances, which can be used to introspect metadata or even instantiate the corresponding device instance.

Working with the SearchResult

Representing a single search result from and its variants, a SearchResult can be used in multiple ways.

This result can be keyed for metadata as in:

In [10]: result = results[0]

In [11]: result['name']
Out[11]: 'my_device'

The HappiItem can be readily retrieved:

In [12]: result.item
Out[12]: Device (name=my_device, prefix=PV:BASE, z=345.5)

In [13]: type(result.item)
Out[13]: happi.device.Device

Or the object may be instantiated:

In [14]: result.get()
          md=Device (name=my_device, prefix=PV:BASE, z=345.5))

See that SearchResult.get() returns the class we expect, based on the device_class.

In [15]: result['device_class']
Out[15]: 'types.SimpleNamespace'

In [16]: type(result.get())
Out[16]: types.SimpleNamespace

There are also some more advance methods to search specific areas of the beamline or use programmer-friendly regular expressions, described in the upcoming sections.

Searching for items on a beamline

To search for items on a beamline such as MFX, one would use the following:

In [17]:'Device', beamline='MFX')
Out[17]: [SearchResult(client=<happi.client.Client object at 0x7fb8785c3160>, metadata={'name': 'my_device2', 'device_class': None, 'args': ['{{prefix}}'], 'kwargs': {'name': '{{name}}'}, 'active': True, 'documentation': None, 'prefix': 'PV:BASE2', 'beamline': 'MFX', 'location_group': 'Loc2', 'functional_group': 'Func2', 'z': 355.5, 'stand': None, 'detailed_screen': None, 'embedded_screen': None, 'engineering_screen': None, 'system': None, 'macros': None, 'lightpath': False, 'parent': None, '_id': 'my_device2', 'creation': 'Wed Jan  6 13:28:22 2021', 'last_edit': 'Wed Jan  6 13:28:22 2021', 'type': 'Device'})]

Searching a range

Searching a Z-range on the beamline, or a range with any arbitrary key is also easy by way of Client.search_range(). For example:

In [18]: client.search_range('z', start=314.4, end=348.6, type='Device')
Out[18]: [SearchResult(client=<happi.client.Client object at 0x7fb8785c3160>, metadata={'name': 'my_device', 'device_class': 'types.SimpleNamespace', 'args': [], 'kwargs': {'name': '{{name}}'}, 'active': True, 'documentation': None, 'prefix': 'PV:BASE', 'beamline': 'XRT', 'location_group': 'Loc1', 'functional_group': 'Func1', 'z': 345.5, 'stand': None, 'detailed_screen': None, 'embedded_screen': None, 'engineering_screen': None, 'system': None, 'macros': None, 'lightpath': False, 'parent': None, '_id': 'my_device', 'creation': 'Wed Jan  6 13:28:22 2021', 'last_edit': 'Wed Jan  6 13:28:22 2021', 'type': 'Device'})]

This would return all devices between Z=314.4 and Z=348.6.

Any numeric key can be filtered in the same way, replacing ‘z’ with the key name.

Searching with regular expressions

Any key can use a regular expression for searching by using Client.search_regex()

In [19]: client.search_regex(name='my_device[2345]')
Out[19]: [SearchResult(client=<happi.client.Client object at 0x7fb8785c3160>, metadata={'name': 'my_device2', 'device_class': None, 'args': ['{{prefix}}'], 'kwargs': {'name': '{{name}}'}, 'active': True, 'documentation': None, 'prefix': 'PV:BASE2', 'beamline': 'MFX', 'location_group': 'Loc2', 'functional_group': 'Func2', 'z': 355.5, 'stand': None, 'detailed_screen': None, 'embedded_screen': None, 'engineering_screen': None, 'system': None, 'macros': None, 'lightpath': False, 'parent': None, '_id': 'my_device2', 'creation': 'Wed Jan  6 13:28:22 2021', 'last_edit': 'Wed Jan  6 13:28:22 2021', 'type': 'Device'})]

Editing Device Information

The workflow for editing a device looks very similar to the code within Creating a New Entry, but instead of instantiating the device you use either Client.find_device() or to grab an existing device from the dataprefix. When the device is retreived this way the class method is overwritten, simply call this when you are done editing the Device information.

In [20]: my_motor = client.find_device(prefix='PV:BASE')

In [21]: my_motor.z = 425.4

In [22]:
Out[22]: 'my_device'


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 Client.add_device() to create a new entry.

Finally, lets clean up our example objects by using Client.remove_device() to clean them from the database

In [23]: device_1 = client.find_device(name='my_device')

In [24]: device_2 = client.find_device(name='my_device2')

In [25]: for device in (device_1, device_2):
   ....:     client.remove_device(device)

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 MongoBackend. Otherwise, the library uses the JSONBackend.