how to use

blocks_fn

when configuring slack alert?

To use

blocks_fn

when configuring a Slack alert in Dagster, you need to define a function that takes in the appropriate context object and outputs a list of message blocks that you want to send to Slack. Message blocks are a way to structure and format the message content in a more interactive and visually appealing way. Here's a step-by-step guide based on the documentation: 1. Define a

blocks_fn

function that accepts a context object and returns a list of dictionaries, each representing a Slack message block. The context object will be either

RunFailureSensorContext

or

FreshnessPolicySensorContext

, depending on the type of sensor you are creating. 2. Within the

blocks_fn

, you can create various types of blocks such as section blocks, divider blocks, image blocks, etc. You can find more information about the different types of blocks and their format in the Slack API documentation on Blocks: https://api.slack.com/reference/block-kit/blocks. 3. Once you have defined your

blocks_fn

, you can pass it as a parameter when creating a Slack sensor or hook in Dagster. The

blocks_fn

will be called when the sensor or hook is triggered, and the returned blocks will be sent as the message content to the specified Slack channel. Here is an example from the documentation that illustrates how you might define a `blocks_fn`:

python def my_blocks_fn(context):     return [         {             "type": "section",             "text": {                 "type": "mrkdwn",                 "text": f"Asset {context.asset_key} is currently {context.minutes_overdue} minutes late!!"             }         },         {             "type": "divider"         },         {             "type": "section",             "text": {                 "type": "mrkdwn",                 "text": "Additional details can go here."             }         }     ]  # Then, when creating a sensor or hook, you would pass `my_blocks_fn` as the `blocks_fn` parameter.

Remember to replace

context.asset_key

and

context.minutes_overdue

with the appropriate attributes from the context object you are using. Please note that the actual usage of

blocks_fn

may vary depending on the specific Dagster function you are using to create the Slack alert. Always refer to the latest Dagster documentation for the most accurate and up-to-date instructions.