Retrieve Data From Queue#

This task retrieves a value from a persistent queue based on a specified queue management type (FIFO, LIFO, or FEFO). If the queue is empty, a default value can be provided and emitted.

Inputs#

Name	Data Type	Description
Queue Name	`String`	The name of the persistence queue to retrieve data from.
Queue Type	`String`	The type of queue management to use for retrieval. Possible values are `FIFO` (First-In, First-Out), `LIFO` (Last-In, First-Out), and `FEFO` (First-Expired, First-Out - requires messages to have an expiration timestamp). Defaults to `FIFO`. If an invalid type is provided, it will fall back to `FIFO`.
Default Value	`any`	The value to emit on the `Value` output if the specified queue is empty when retrieval is attempted.
Activate	`any`	When this input transitions to a truthy value, the task attempts to retrieve a value from the specified `Queue Name` using the selected `queueType`.

Outputs#

Name	Data Type	Description
Value	`any`	Emits the value retrieved from the queue. If the queue is empty and a `Default Value` is provided, that value will be emitted instead.
Success	`Boolean`	Emits `true` when a value is successfully retrieved from the queue (or the `Default Value` is emitted if the queue is empty).
Error	`Error`	Emits an `Error` object if any issue occurs during the retrieval process, such as an invalid queue name or an error accessing the data store.

Settings#

On the General Tab, you have the usual general settings and the following settings:

Name	Data Type	Default	Description	Values
Default Queue Name	`String`	No	Default persistence queue name to retrieve data from.
Default Queue Type	`String`	No	Default queue type to use for retrieval. Defaults to `FIFO`.	`FIFO`, `LIFO` or `FEFO`
Default Value	`any`	No	The value to emit on the `Value` output if the specified queue is empty when retrieval is attempted.

Behavior#

When the Activate input receives a true value, the task attempts to retrieve the next value from the queue specified by Queue Name, based on the Queue Type.

FIFO (First-In, First-Out): Retrieves the oldest value that was added to the queue.
LIFO (Last-In, First-Out): Retrieves the most recently added value to the queue.
FEFO (First-Expired, First-Out): Retrieves the oldest value that has an expiration timestamp that has passed. If no expired messages is found on the queue, then it will behave as FIFO (retrieves oldest item in the queue).

If the specified Queue Name does not exist, the task will emit an error.

If the queue exists but is empty when retrieval is attempted, the task will emit the value provided in the Default Value input on the Value output and true on the success output. If no Default Value is provided and the queue is empty, the Value output will emit null or undefined, and success will still be true (indicating a successful attempt to retrieve).

If the provided Queue Type is not one of the valid options (FIFO, LIFO, FEFO), the task will log a warning and default to FIFO behavior for that retrieval attempt.

Each time the Activate input is triggered, the task attempts to retrieve and remove a single value from the queue (except in cases where the queue is empty and the Default Value is used).

Remarks#

This task assumes that the queue has been previously created and populated by a task like "Store in Queue".
For the "FEFO" queue type to function correctly, the values stored in the queue should have associated expiration timestamps. If no item with expiration time is available in the queue then the oldest item in the queue is retrieved (mimics FIFO queue type behavior).
Consider the implications of the chosen Queue Type on the order in which values are processed from the queue, as this can significantly affect the workflow's logic.