labthings_fastapi.dependencies.metadata

FastAPI dependency to get metadata from all Things.

This module defines a FastAPI dependency (see Dependencies) that will retrieve metadata from every Thing on the server. This is intended to simplify the task of adding metadata to data collected by Thing instances.

Functions

thing_states_getter(→ Callable[[], ...)

Generate a function to retrieve metadata from all Things in this server.

Module Contents

labthings_fastapi.dependencies.metadata.thing_states_getter(request: fastapi.Request) → Callable[[], collections.abc.Mapping[str, Any]]

Generate a function to retrieve metadata from all Things in this server.

Warning

This function is deprecated in favour of the ThingServerInterface, which is available as a property of every Thing. See ThingServerInterface.get_thing_states for more information.

This is intended to make it easy for a Thing to summarise the other Things in the same server, as is often appropriate when embedding metadata in data files. For example, it’s used to populate the UserComment EXIF field in images saved by the OpenFlexure Microscope.

This is intended for use as a FastAPI dependency, so the request argument will be supplied automatically.

This function does not collect the metadata when it is run. Instead, we return a function that will collect the metadata when it is called. This delays collection of metadata until it is needed.

Delaying collection of metadata is useful because FastAPI dependencies are evaluated only once, before the action starts. If we collect metadata then, there is no way for it to change during an action, so the metadata may be out of date.

For example, if we take a Z stack of microscope images, we need to collect metadata after each image in order to ensure the recorded position of the stage is up to date.

Bear in mind that actions may call other actions, so even if you have a very simple or short action that will not cause metadata to change, it may be called by a longer action where that isn’t true. Dependencies will be evaluated before the calling action starts, so stale metadata is still a possibility in very short actions.

Parameters:

request – the fastapi.Request object, supplied automatically when used as a dependency. See Dependencies.

Returns:

a function that returns a dictionary of metadata.