有没有办法在EventHubConsumerClient (azure-sdk-for-python)中的on_event函数上传递额外的参数？

Question

这个例子来自azure-sdk- for -python for -python for Azure Event Hubs for a consumer。

#!/usr/bin/env python

# --------------------------------------------------------------------------------------------
# Copyright (c) Microsoft Corporation. All rights reserved.
# Licensed under the MIT License. See License.txt in the project root for license information.
# --------------------------------------------------------------------------------------------

"""
An example to show receiving events from an Event Hub with checkpoint store asynchronously.
In the `receive` method of `EventHubConsumerClient`:
If no partition id is specified, the checkpoint_store are used for load-balance and checkpoint.
If partition id is specified, the checkpoint_store can only be used for checkpoint.
"""

import asyncio
import os
from azure.eventhub.aio import EventHubConsumerClient
from azure.eventhub.extensions.checkpointstoreblobaio import BlobCheckpointStore

CONNECTION_STR = os.environ["EVENT_HUB_CONN_STR"]
STORAGE_CONNECTION_STR = os.environ["AZURE_STORAGE_CONN_STR"]
BLOB_CONTAINER_NAME = "your-blob-container-name"  # Please make sure the blob container resource exists.


async def on_event(partition_context, event):
    # Put your code here.
    print("Received event from partition: {}.".format(partition_context.partition_id))
    await partition_context.update_checkpoint(event)


async def receive(client):
    """
    Without specifying partition_id, the receive will try to receive events from all partitions and if provided with
    a checkpoint store, the client will load-balance partition assignment with other EventHubConsumerClient instances
    which also try to receive events from all partitions and use the same storage resource.
    """
    await client.receive(
        on_event=on_event,
        starting_position="-1",  # "-1" is from the beginning of the partition.
    )
    # With specified partition_id, load-balance will be disabled, for example:
    # await client.receive(on_event=on_event, partition_id='0'))


async def main():
    checkpoint_store = BlobCheckpointStore.from_connection_string(STORAGE_CONNECTION_STR, BLOB_CONTAINER_NAME)
    client = EventHubConsumerClient.from_connection_string(
        CONNECTION_STR,
        consumer_group="$Default",
        checkpoint_store=checkpoint_store,  # For load-balancing and checkpoint. Leave None for no load-balancing.
    )
    async with client:
        await receive(client)


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(main())

有没有办法在on_event函数中传递额外的参数。例如，在这个消费者中，我收到来自生产者的消息，假设我需要在数据库中插入一些数据，我需要传递一个打开的数据库连接。我该如何着手做这样的事情呢？

repository中的所有示例都是相同的，on_event有这两个参数，坦率地说，我不知道它们是从哪里来的。

谢谢

Answer 1

on_event(partition_context, event)是一个回调方法，它被传递给client.receive方法，告诉它“收到事件时以这种方式处理它”。显然，on_event必须遵循一个固定的方法'signature‘，以便客户端接收方能够在接收到事件时调用回调。即使可以向on_event传递额外的参数，它对您也是无用的，因为您没有调用该方法。

我建议你这样做。在on_event方法外声明一个字段，从某个声明方法初始化它，然后在on_event内部访问它，如下所示：

#!/usr/bin/env python

# --------------------------------------------------------------------------------------------
# Copyright (c) Microsoft Corporation. All rights reserved.
# Licensed under the MIT License. See License.txt in the project root for license information.
# --------------------------------------------------------------------------------------------

"""
An example to show receiving events from an Event Hub with checkpoint store asynchronously.
In the `receive` method of `EventHubConsumerClient`:
If no partition id is specified, the checkpoint_store are used for load-balance and checkpoint.
If partition id is specified, the checkpoint_store can only be used for checkpoint.
"""

import asyncio
import os
from azure.eventhub.aio import EventHubConsumerClient
from azure.eventhub.extensions.checkpointstoreblobaio import BlobCheckpointStore

CONNECTION_STR = os.environ["EVENT_HUB_CONN_STR"]
STORAGE_CONNECTION_STR = os.environ["AZURE_STORAGE_CONN_STR"]
BLOB_CONTAINER_NAME = "your-blob-container-name"  # Please make sure the blob container resource exists.

MY_DATABASE_CONNECTION = None

async def on_event(partition_context, event):
    # Put your code here.
 
    # Use MY_DATABASE_CONNECTION as needed
    
    print("Received event from partition: {}.".format(partition_context.partition_id))
    await partition_context.update_checkpoint(event)


async def receive(client):
    """
    Without specifying partition_id, the receive will try to receive events from all partitions and if provided with
    a checkpoint store, the client will load-balance partition assignment with other EventHubConsumerClient instances
    which also try to receive events from all partitions and use the same storage resource.
    """
    MY_DATABASE_CONNECTION = <initilize it>

    await client.receive(
        on_event=on_event,
        starting_position="-1",  # "-1" is from the beginning of the partition.
    )
    # With specified partition_id, load-balance will be disabled, for example:
    # await client.receive(on_event=on_event, partition_id='0'))


async def main():
    checkpoint_store = BlobCheckpointStore.from_connection_string(STORAGE_CONNECTION_STR, BLOB_CONTAINER_NAME)
    client = EventHubConsumerClient.from_connection_string(
        CONNECTION_STR,
        consumer_group="$Default",
        checkpoint_store=checkpoint_store,  # For load-balancing and checkpoint. Leave None for no load-balancing.
    )
    async with client:
        await receive(client)


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(main())