different values for jmeter ${__UUID} in loop

Question

In my BSF preprocessor (language javascript), I am generating post data such as

 var totalCustomer = 2;
 var data = { "customers": [] };
 for(i=1; i<=totalCustomer; i++){

     // in all iteration getting same value for ${__UUID} 

     var customer = {
         "id": "${__UUID}"
     }
     data.customers.push(customer);
 }
 vars.putObject("data",JSON.stringify(data));

I guess it is compiled once and looked up for the value in subsequent iterations.

Is there any way I can generate different guid using ${__UUID} for each iteration?

Answer 1

1. Replace ${__UUID} with UUID.randomUUID().toString(). Don't inline JMeter variables and functions into script, it's not very good practice and may lead to unexpected behavior (as in your case). Particular for your scenario it's better to call UUID class methods directly.
2. Don't use BSF test elements, they're not very efficient from performance side of things. Consider using JSR223 test elements and Groovy language. See Beanshell vs JSR223 vs Java JMeter Scripting: The Performance-Off You've Been Waiting For! for explanation, benchmarks, groovy engine installation details and scripting best practices.