Access Properties of a new Stream in Esper

Question

I'm starting a new stream by using the statement: "insert into middleLayerStream select id, 'response' as constraint from[...]"

Afterwards I'm starting a SELECT-query to the middleLayerStream. In die update-function of my middleLayerStream I want du print out the properties of the stream.

This is my update Function:

public class MiddleLayerListener impplement UpdateListener{
   public void update(EventBean[] newEvents, EventBean[] oldEvents){
      EventBeant[] event = newEvents[0];
      System.out.println(event.getUnderlying());
   }
}

When the update-function is called, I don't get the properties but this stetement instead:

{a=MapEventBean eventType=com.espertech.esper.event.map.MapEventType@52500920, b=MapEventBean eventType=com.espertech.esper.event.map.MapEventType@52500920}

How do I get access to the properties?

I just found out, that event is not a simple EventBean but a MapEventBean. Maybe it's because two different types of events (but with the same properties) are inserted into the stream. But how can i handle a MapEventBean and get the properties out of it?

Thank you very much for your help.

Your post is incorrect. What you have cut&pasted is the output of System.out.println(event) and not System.out.println(event.getUnderlying()). — user650839, Dec 11 '20 at 15:12
That is exactly the output I get when I call event.getUnderlying(). And I have no idea why, because usually .getUnderlying() would return a list of the properties but it doesn't — n.muc.ruh, Dec 11 '20 at 16:06
On second look yes event properties can themselves be EventBean instances — user650839, Dec 11 '20 at 16:51
And how do I get access on the properties of the Eventbeans? — n.muc.ruh, Dec 11 '20 at 16:54

user650839 · Answer 1 · 2020-12-11T17:02:34.593

0

The EventBean interface offers a "get" method that returns an event property value by name.

public void update(EventBean[] newEvents, EventBean[] oldEvents){
  for (EventBean event : newEvents) {
    System.out.println(event.get("id"));
  }
}

You left off the "from" in your post so it wasn't possible to see what was selected. I assume that you have a pattern in the "from" such as "a=A -> b=B".

In the case of a pattern returning a nested event event.get("a.id") or event.get("a") or event.getFragment("a") or select a.id as id from [...] would do.

edited Dec 11 '20 at 17:02

answered Dec 11 '20 at 12:22

user650839

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Yes, I am using this in my other listeners and it's working totally fine, but when I do so in this listener, I just don't get any output. Nothing happens. – n.muc.ruh Dec 11 '20 at 16:08
Whats does "nothing happens" mean...? – user650839 Dec 11 '20 at 16:52
No error is occurring and the engine just keeps on going.. – n.muc.ruh Dec 11 '20 at 16:54
When the listener throws an exception, and since the runtime invokes the listener, make sure you have logging or code your listener so it doesn't have an exception. – user650839 Dec 11 '20 at 17:05

score 0 · Answer 2 · answered Dec 11 '20 at 17:04

Ok I got it.. In my SELECT Query that ist starting the update function of MiddleLayerListener I selected * like

SELECT * from pattern[every a=.... -> b=...]

So of course there a both events in a MapEventBean (a and b). By specifying the SELECT Query like:

SELECT a.id as id from pattern...

In now have only the wanted properties in my stream and can access them as normal.

Wow.. that took me a whole day of desperation :D

Thank your very much for your help :)

Reading the docs may help. The first example is in 7.2.2. Patterns in EPL — user650839, Dec 11 '20 at 17:41

Access Properties of a new Stream in Esper

2 Answers2