Read a string from a file with a dynamic name in JMeter - jmeter

Question

My test plan contains a thread group that looks like that :
Only once controller : Login to application
CSV Data Set Config : Info used to login to application
Only once controller
HTTP Request : POST login information
Loop controller (10 times)
HTTP Request : POST add a "comment" to a "question"
My CSV dataset contains these fields :
username
password
group_id
A user have access to a question depending on it's group_id. I want to add 10 comments per thread to different questions.
My idea was to build a file like questions_by_group_${group_id}.txt containing some ids of questions that the ${group_id} would have access. Then I could do ${__StringToFile(questions_by_group_${group_id}.txt)} in the POST parameter value to add a comment. Using __StringToFile function should loop through lines of my file at every call. That way I can add many comments to many different questions.
The problem is that JMeter seems to open the file one time and share it for every thread (even thought I know that the ${group_id} changes for every thread.
I tried many things like
${__StringFromFile(questions_by_group_${group_id}.txt)}
${__StringFromFile(${__eval(questions_by_group_${group_id}.txt)})}
${__eval(${__StringFromFile(${__eval(questions_by_group_${group_id}.txt)})})}
but nothing works.

Answer 1

StringFromFile works this way by default, read:
__StringFromFile
You could organize your csv like this:
username, password, group_id , commentID1, commentID2....
Then put CSV Data Set Config before Once Only Controller.
Set Sharing Mode to All threads for example.
Finally just use variables instead of using __StringFromFile.
It's not the best solution as you have to build this file and repeat group_id ids.
Another option, if your number of groups is not very big, would be to do this in a setUp Thread Group:
read a CSV file containing:
groupID1, IDA1, IDA2,....
groupID2, IDB1, IDB2,....
...
set one property per group __setProperty or calling this inside a Beanshell Sampler:
JMeterUtils.setProperty(propertyName, propertyValue);
Then in your controller, use a Beanshell Sampler to get ids using:
JMeterUtils.getProperty(propertyName);
I must say I hate all these solutions :-)