define a sensor

In Dagster, a sensor is a function that you can define to monitor external events and trigger runs of your jobs when certain conditions are met. To define a sensor, you use the

@sensor

decorator provided by Dagster. The decorated function is an evaluation function that takes in a

SensorEvaluationContext

and can yield

RunRequest

objects to create job runs or

SkipReason

objects to indicate why no runs were created. Here's a basic example of how to define a sensor:

python from dagster import sensor, SensorEvaluationContext, RunRequest  @sensor(job=my_job) def my_sensor(context: SensorEvaluationContext):     # Your custom logic to check for external events goes here     # For example, you might check for a new file in a directory     if new_data_available():         # If the condition is met, create a RunRequest to trigger a job run         run_config = {"solids": {"my_solid": {"config": {"param": "value"}}}}         yield RunRequest(run_key="unique_run_key", run_config=run_config)     else:         # If the condition is not met, you can yield a SkipReason         yield SkipReason("No new data to process")

In this example,

my_job

is the job that you want to trigger. The

new_data_available

function represents a custom check for external events, such as the arrival of new data. If the condition is met, a

RunRequest

is yielded with a unique

run_key

and the necessary

run_config

for the job. If the condition is not met, a

SkipReason

is yielded to indicate why no run was created. Remember to replace

my_job

,

new_data_available

, and the

run_config

with your actual job, condition-checking logic, and configuration, respectively. This is a simplified example to illustrate the concept. In practice, your sensor's logic can be as simple or complex as needed to meet your requirements.