Map Downlink

A MapDownlink synchronizes a shared real-time key-value map with any Web Agent lane backed by a map. In addition to map lanes, this includes join value lanes and join map lanes, which are maps where each entry is its own value lane or maps lane, respectively. In addition to the standard Downlink callbacks, MapDownlink supports registering did_update, and did_remove callbacks for observing changes to downlinked map state — whether remote or local. did_update is invoked when an existing map key is updated or a new key is added. did_remove gets called when a map key is removed.

Create a MapDownlink with a SwimClient’s downlink_map method.

Use the get method to get the value associated with a given key and get_all to get all values. Use the put method to update the value associated with a key and use the remove method to remove a key and its associated value.

from swimos import SwimClient

with SwimClient() as swim_client:
    host_uri = 'warp://example.com'
    node_uri = '/hotel/lobby'
    lane_uri = 'elevators'

    map_downlink = swim_client.downlink_map()
    map_downlink.set_host_uri(host_uri)
    map_downlink.set_node_uri(node_uri)
    map_downlink.set_lane_uri(lane_uri)
    map_downlink.open()

    map_downlink.get('guest')  # get the locally cached value associated with the key
    map_downlink.set('service', 'elevator')  # locally and remotely insert a new entry
    map_downlink.delete('parking')  # locally and remotely remove an existing entry

The SwimClient will ensure that the downlink is continuously made consistent with the remote lane. Using did_update and did_remove callbacks, applications can update dependent components to keep them consistent with the shared state of the remote map lane in network real-time. Callbacks can be defined as shown below.

from swimos import SwimClient


async def custom_did_update(key, new_value, old_value):
    print(f'Link watched {key} changed to {new_value} from {old_value}')


async def custom_did_remove(key, value):
    print(f'Link removed {key} with value {value}')


with SwimClient() as swim_client:
    host_uri = 'warp://example.com'
    node_uri = '/hotel/lobby'
    lane_uri = 'elevators'

    map_downlink = swim_client.downlink_map()
    map_downlink.set_host_uri(host_uri)
    map_downlink.set_node_uri(node_uri)
    map_downlink.set_lane_uri(lane_uri)

    map_downlink.did_update(custom_did_update)
    map_downlink.did_remove(custom_did_remove)

    map_downlink.open()
Value Downlink
Event Downlink