How to assign a value using a siddhi query?

Question

I need to assign a value to a particular attribute in a stream by checking a condition.

How do I do it?

e.g

if a person's name is 'John' and I need to modify his name into 'Peter' and insert into another stream, how do I do it?

from myStream [name == 'John']
select *
insert into outStream;

Answer 1

define stream myStream (name string, attribute1 int, attribute2 bool);

from myStream [name == 'John']                  --This filter matches any event with name equal to 'John'
select "Peter" as name, attribute1, attribute2  --Replaces the current name with 'Peter'
insert into outStream;

Example 1

Input:

{Dilini, 123, true}

Output:

(there'll be no output, since the name doesn't satisfy the condition in the filter, name=='John')

Example 2

Input:

{John, 123, true}

Output:

{Peter, 123, true}

Refer 'Query Projection' capabilities in Siddhi. Check the action: 'Introducing the default value'.