StreamTransformer usage issue: How to get value of inbound entry?

[sumeet70 <su...@gmail.com>]

If we attach a receiver to the data streamer then we must call the put method
to get value into the cache.

But I am unable to retrieve the new value of the cache entry inside
StreamTransformer.from. When I cal e.getValue() in the following snippet, it
returns the previously stored cached value for the current key. How can I
get the value being currently added ?

    CacheConfiguration<Integer, Integer> cacheConfiguration = new
CacheConfiguration("SAMPLE");
    IgniteCache<Integer, Integer> igniteCache =
ignite.getOrCreateCache(cacheConfiguration);

    try (IgniteDataStreamer<Integer, Integer> dataStreamer =
ignite.dataStreamer(igniteCache.getName())) {

        dataStreamer.allowOverwrite(true);
        dataStreamer.receiver(StreamTransformer.from((e, arg) -> {

            System.out.println("Key:" + e.getKey());
            System.out.println("Val:" + e.getValue()); //This always returns
the previously stored value

            if(e.getValue() == null){
                igniteCache.put(e.getKey(), 0);
            }
            return null;
       }));
   dataStreamer.addData(1, 1);
   dataStreamer.addData(2, 1);
   dataStreamer.addData(1, 2); 


Although I am able to solve my problem using the StreamVisitor instead of
the StreamnTransformer but I had to struggle with StreamTransformer
symantics for a significant amount of time. I am still not sure if I am
thinking about Stream Transformer correctly or not.




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Re: StreamTransformer usage issue: How to get value of inbound entry?

[Artem Shutak <as...@gridgain.com>]

You can find examples here:
https://github.com/apache/ignite/blob/master/examples/src/main/java/org/apache/ignite/examples/streaming/StreamTransformerExample.java.



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Re: StreamTransformer usage issue: How to get value of inbound entry?

[Artem Shutak <as...@gridgain.com>]

Hi,

StreamerTransformer javadoc says "Convenience adapter to transform update
existing values in streaming cache based on the previously cached value.".
So, you see right behavior.

I recommend you look at StreamTransformerExample for examples of usage
StreamerTransformer.

So, for your use-case StreamVisitor is a right chose.

Thanks,
Artem.



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