TRANSACTION ISOLATION LEVEL in postgres before loop

[Anonymous]

Hello, 

I need to use the Transaction isolation level to guarantee that the data is the same at the end of the loop. I have a loop to read from a database in batch.

The thing is that this is returning an error: SET TRANSACTION ISOLATION LEVEL must be called before any queryException in component tDBInput_2

In the image, I have a piece of job talend, and the transaction code is in tDBRow_2 out of the loop like I think it must be. I do not have a commit, because I'm reading to a file.

My question is: how can I do this to guarantee the coherence of that the data?

Anyone can help me?