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State of the World (SOW)

AMPS State of the World (SOW) allows you to automatically keep and query the latest information about a topic on the AMPS server, without building a separate database. Using SOW lets you build impressively high-performance applications that provide rich experiences to users. The AMPS Python client lets you query SOW topics and subscribe to changes with ease.

Performing SOW Queries​

To begin, we will look at a simple example of issuing a SOW query.

for message in client.sow("orders", "/symbol='ROL'"):
    if message.get_command() == AMPS.Message.Command.GroupBegin:
        print("--- Begin SOW Results ---")
    if message.get_command() == AMPS.Message.Command.SOW:
        print(message.get_data())
    if message.get_command() == AMPS.Message.Command.GroupEnd:
        print("--- End SOW Results ---")

In the example above, the Client.sow() convenience method is used to execute a SOW query on the orders topic, for all entries that have a symbol of 'ROL'.

As the query executes, messages containing the data of matching entries have a Command of value "sow" (provided as a constant value, AMPS.Message.Command.SOW), so as those arrive, we write them to the console.

As with subscribe, the sow command also provides an asynchronous mode, where you provide a message handler.

def on_message_handler(message):
    if message.get_command() == AMPS.Message.Command.GroupBegin:
        print("--- Begin SOW Results ---")
    if message.get_command() == AMPS.Message.Command.SOW:
        print(message.get_data())
    if message.get_command() == AMPS.Message.Command.GroupEnd:
        print("--- End SOW Results ---")

def execute_sow_query(client):
    return client.execute_async(             \
            AMPS.Command("sow")              \
                .set_topic("orders")         \
                .set_filter("/symbol='ROL'"),\
            on_message_handler)

execute_sow_query(client)

In the example above, the execute_sow_query() function invokes Client.execute_async() to initiate a SOW query on the orders topic, for all entries that have a symbol of 'ROL'.

As the query executes, the on_message_handler() function is invoked for each matching entry in the topic. Messages containing the data of matching entries have a Command of value sow, so as those arrive, we write them to the console.