Negation for "every" statement? WSO2 CEP / Siddhi

Question

Is there a simple way to negate the "every" statement? I am trying to implement a control tool that checks incoming purchase orders and requisitions. For each purchase order (PO) a requisition (REQ) has to be created before. The following code detects PO/REQ-pairs that match (positives) but I need all POs that do not have a corresponding REQ (negatives).

from every a1 = PO -> b1 = REQ[a1.ITEM_ID == b1.ITEM_ID and a1.QUANTITY == b1.QUANTITY and a1.CREATED_BY == b1.CREATED_BY] within 1 day select 'No REQ created before' as ALERT_MESSAGE insert into ALERT;

Answer 1

You can refer to sample on detecting non-occurrences with patterns. However, since you want to check whether REQ event came before PO event you might need to use in-memory event tables to cater your requirement. Refer to the following sample on achieving the same using in-memory tables;

@Import('REQStream:1.0.0')
define stream REQ (ITEM_ID int, QUANTITY int, CREATED_BY string);

@Import('POStream:1.0.0')
define stream PO (ITEM_ID int, QUANTITY int, CREATED_BY string);

@Export('ALERTStream:1.0.0')
define stream ALERT (ITEM_ID int, ALERT string);

define table REQ_TABLE (ITEM_ID int, QUANTITY int, CREATED_BY string);

define trigger DAILY_TRIGGER at every 1 day;

from REQ
insert into REQ_TABLE;

-- check whether request exists before the purchase
from PO[not((REQ_TABLE.ITEM_ID == ITEM_ID and REQ_TABLE.QUANTITY == QUANTITY and REQ_TABLE.CREATED_BY == CREATED_BY) in REQ_TABLE)] 
select ITEM_ID, 'No REQ created before' as ALERT
insert into ALERT;

-- purge reauests table daily
from DAILY_TRIGGER join REQ_TABLE
select REQ_TABLE.ITEM_ID, REQ_TABLE.QUANTITY, REQ_TABLE.CREATED_BY
insert into PURGE_STREAM;

-- if there's no matching purchase order came up for previous day
from PURGE_STREAM
select ITEM_ID, 'No purchase order came up for a day' as ALERT
insert into ALERT;

from PO
insert into DEL_STREAM;

from PURGE_STREAM
insert into DEL_STREAM;

-- delete corresponding request from table
from DEL_STREAM 
delete REQ_TABLE
    on REQ_TABLE.ITEM_ID == ITEM_ID and REQ_TABLE.QUANTITY == QUANTITY and REQ_TABLE.CREATED_BY == CREATED_BY;