Yeah, that was something that kinda flew under the radar. Definitely improved
the API.
Not really related, but on the note of things you may not realize, with that
code snippet :)
If you have access to update the processor mentioned here, you should avoid
using session.putAttribute many times.
Under the hood, in order to maintain object immutability it has to create a new
FlowFile object (and a new HashMap of all attributes!)
for every call to putAttribute. So if there are 100 attributes that match
that’s potentially a huge amount of garbage getting created. Instead,
you could just use:
```
final Map<String, String> attributes = new HashMap<>();
flowFile.getAttributes().forEach( (key, value) -> {
if (key.startsWith(“foo”)) {
attributes.put(“original-“ + key, value);
}
}
flowFIle = session.putAllAttributes(flowFile, attributes);
```
Thanks
-Mark
> On May 8, 2024, at 10:30 AM, Michael Moser <moser...@gmail.com> wrote:
>
> Wow, thanks for this information! Just last week I saw code that modified
> attributes in a stream:
>
> flowFile.getAttributes().entrySet().stream().filter(e ->
> e.getKey().startsWith("foo"))
> .forEach(e -> session.putAttribute(flowFile, "original-" + e.getKey,
> e.getValue()));
>
> and I wondered how that could possibly work since the return value of
> session.putAttribute is ignored! Now I know.
>
> -- Mike
>
> On Tue, May 7, 2024 at 3:02 PM Russell Bateman <r...@windofkeltia.com>
> wrote:
>
>> Yes, what you described is what was happening, Mark. I didn't display
>> all of the code to the session methods, and I did re-read the in-coming
>> flowfile for different purposes than I had already read and written it.
>> So, I wasn't helpful enough. In the end, however, I had forgotten,
>> immediately after the call to session.putAllAttributes(), to update the
>> resulting flowfile for passing to session.transfer(). That solved it for
>> 1.1.2 which wasn't necessary for 1.13.2 or later versions. Being
>> helpful, the newer versions made me a spoiled, entitled child and I will
>> repent immediately.
>>
>> Thanks, guys! DevOps are happy they don't have to upgrade the customers
>> to NiFi 1.13.2. (In a way, I'm unhappy about that, but...).
>>
>> Best regards,
>>
>> Russ
>>
>> On 5/7/24 11:53, Mark Payne wrote:
>>> The call to session.putAttribute would throw an Exception because you
>>> provided an outdated version of the flowFile (did not capturing the
>>> result of calling session.write)
>>>
>>> Now, as NiFi matured, we found that:
>>> (a) for more complex processors that aren’t just a series of sequential
>>> steps it becomes difficult to manage all of that bookkeeping.
>>> (b) it was not intuitive to require this
>>> (c) the ProcessSession already had more or less what it needed in order
>>> to determine what the most up-to-date version of the FlowFile was.
>>>
>>> So we updated the ProcessSession to automatically grab the latest
>>> version of the FlowFile for these methods. But since you’re trying to
>>> run an old version, you’ll need to make sure that you capture all of
>>> those outputs and always keep track of the most recent version of a
>>> FlowFile.
>>
