Thanks a bunch for this response, Steve. It's far more helpful to get a
meaningful, fleshed-out response than to get terse, sarcastic non-answers. I'm
already struggling enough with trying to use JMeter... I don't need more grief
because I don't intuitively understand quirks in poorly-documented software. :)
I especially appreciate the info. on common "gotchas." I know my code's worst
enemy is my own typing. It looks to me like my big mistake was thinking that
the User Defined Variables was useful for evaluating expressions and assigning
them to variables. It's obviously the wrong component to use for what I'm
trying to accomplish.
The problem I'm trying to solve involves cycling through pagination for
different media types. For example, we have pages which allow users to browse
through several media categories (movies, audio, etc., as well as an "all
media" category) and I wanted to ensure that I touched them all. Since the
tests I'm trying to write will upload images, etc., the total number of assets
for each media type will change, which will affect pagination. We're
displaying four items per page, so I need to extract the total # of media items
per category (which was totally easy to do with the Regular Expression
Extractor) and then divide that result by 4 (seemingly
nigh-unto-freaking-impossible). I then need to add 1 to the total if there's a
remainder (modulus). So, I'm trying to do this:
assets_per_category = numeric_result_from_the_regex
num_of_pages_for_category = assets_per_category / 4
if assets_per_category % 4 > 0
num_of_pages_for_category += 1
end
I have no idea as to where to stick this in JMeter, and that's frustrating me
to the point where I'm coming up with creative ideas as to what JMeter can
stick where. ;)
There are all kinds of components to do things that would be otherwise
dirt-simple in a code block, but there doesn't seem to be a place to
stick a code block.
> What I would like to see in jmeter though is a
> element that can be used just for processing
> expressions, etc. It seems many of the functions,
> etc are intended to used 'in line' vs the model
> of modifying variables and expressions first,
> then passing them into the samplers/etc. Maybe
> an 'executor' block :)
This is exactly what I've been trying to wrap my head around and having
something like a Expression/Block Processor Component would have helped me
tremendously. I've been trying to get a BeanShell script to work, but JMeter's
not finding the jar which is sitting right next to it. /sigh /insert lengthy
rant about how hard it is to make Java do stuff if you're not a Java
SuperGenius.
> It's confusing at first, but once you know what's
> happening its not so bad to work with.
So you're suggesting that once my head is caved-in from beating my head on my
desk in frustration that there's a light at the end of the tunnel? SUH-WEET!
:)
> You must live with the assumption that if jmeter
> doesn't understand the reference, it will just be
> passed as a literal string.
I noticed that early-on, and yes, it was surprising. I'm coming to appreciate
the fact that JMeter generally does things 180 degrees of what I find to be
intuitive.
> The rest is just coping with no syntax or reference
> checking... So the burden of debugging is on you.
Is "Screw you, Tester" the official motto of JMeter? It looks like it was
designed for people with little-to-no programming experience yet it requires
knowledge of a bunch of stuff that I frankly didn't want to learn just to make
it do simple stuff like dividing numbers.
I'm glad that I finally know to use ${__jexl(a+b)} (although NOT in UDV), but
seriously, why is the syntax to do simple math so convoluted? I'd NEVER have
guessed that I needed to use something called "jexl" to do simple evals.
That said however, now that I understand what it is and why it might be useful
to me, I think jexl is kinda cool and that the jexl syntax is "obvious." Two
sentences in the documentation would have saved me hours of grief.
"jexl, javascript, or [whatever voodoo I don't understand] can be used to
evaluate expressions."
Actually, just that one sentence would have made a big difference.
> Yes you must use javascript, but its stupid simple.
> Javascript help on operators
Yeah, now that I understand that's the way JMeter works, I can deal. I
appreciate the link/reference, though I already know 'nuff JS to be dangerous.
:)
In my original post, I was trying to use UDV for this purpose but have come to
an appreciation of the fact that it's just the flat-wrong thing to do.
However, I still don't know the answer to "WHERE does this kind of stuff go?"
Do I have to insert these inline somewhere?
Again, many thanks for the helpful response,
- Dan
----- Original Message ----
From: Steve Kapinos <[EMAIL PROTECTED]>
To: JMeter Users List <[email protected]>
Sent: Friday, April 11, 2008 4:53:34 AM
Subject: RE: Understanding How to Twiddle Values in JMeter
>So, you're suggesting that I should learn Jexl so that I can divide one
number by another in JMeter?
Yes you must use javascript, but its stupid simple. Javascript help on
operators
http://www.w3schools.com/js/js_operators.asp
Functions are very simple
${__jexl(${log1ID}+1)}
>Wow, that's absolutely NOT what I'd expect and I don't see that
mentioned anywhere in the documentation.
I came across this as well.. Basically you can't reference another
variable in a UDV that was defined in that same UDV element. Things
aren't ready till the end of the element. sebb added to the
documentation in-progress at that point to help make that clear.
>*Should* work and *does* work are totally different things. My
experience with JMeter suggests that JMeter is
>remarkably inconsistent as to what text fields/etc. are actually
interpreted
It's confusing at first, but once you know what's happening its not so
bad to work with. You must live with the assumption that if jmeter
doesn't understand the reference, it will just be passed as a literal
string. This includes undefined variable names or syntax mismatches.
Basically, instead of stopping and erroring, its going to continue and
pass that as a string 'as is' rather then evaluate it.
Common things I found that trip you up
- case sensativity in function and variable names
- the usual { vs ( typos
- typos or mismatches in variable or function names
People are accustomed to the program halting on syntax checking or
references and jmeter simply doesn't do that. So any errors must be
caught through monitoring the values being used. Only when you get
invalid parameters in some of the samplers, etc do you typically get an
exception at run time.
The key is to use the debug sampler often when writing the script to
monitor the variables and properties to ensure you are manipulating what
you expect. Every time I had problems like you described, it was
typically one of the above problems. The UDV issue of referencing the
variable that was just defined in the same element has been the only
real problem I've encounter. The rest is just coping with no syntax or
reference checking... So the burden of debugging is on you.
What I would like to see in jmeter though is a element that can be used
just for processing expressions, etc. It seems many of the functions,
etc are intended to used 'in line' vs the model of modifying variables
and expressions first, then passing them into the samplers/etc. Maybe an
'executor' block :)
----- Original Message ----
From: sebb <[EMAIL PROTECTED]>
To: JMeter Users List <[email protected]>
Sent: Thursday, April 10, 2008 6:20:03 PM
Subject: Re: Understanding How to Twiddle Values in JMeter
On 11/04/2008, Dan Tripp <[EMAIL PROTECTED]> wrote:
> Howdy All,
>
> I'm trying to perform some simple calculations with data I've
extracted using an HTTP sampler and the Regular Expression Extractor. I
have no problem getting the values I need/want/expect from the Regex,
but I can't seem to add numbers together, and I can't seem to figure out
*WHERE* the calculations should go.
>
> The simplest sample I've come up with looks like this:
>
> Test Plan
> + Thread Group
> - User Defined Variables
> - Debug Sampler
> - View Results Tree
> Workbench
>
> In User Defined Variables, I have:
>
> Name Value
> ====== ================================
> var1 __eval(30 + 6)
__eval() does not evaluate numeric expressions.
You can use intSum() for adding/subtracting numbers, otherwise use Jexl.
> var2 ${__eval(30 + 6)}
> var3 10 / 4
> var4 ${__eval(10 / 4)}
> var5 ${__time(YMD)}
> column uname
> table users
> sql SELECT ${column} FROM ${table}
>
> The output I see from the Debug Sampler is NOT what I'd expect:
>
> var1 = __eval(30 + 6)
> var2 = ${__eval(30 + 6)}
> - I was hoping to get "36"
>
> var3 = 10 / 4
> var4 = ${__eval(10 / 4)}
> - I was hoping to get "2"
>
> var5 = ${__time(YMD)}
> - I was hoping to get "20080410"
>
> column = uname
> table = users
> sql = SELECT ${column} FROM ${table}
> I was hoping to get "SELECT uname FROM users"
UDV variables are not defined until the entire element has been
processed.
If you put sql in a separate UDV it should work.
> It may be the case that User Defined Variables is just a convenience
component which makes it easier to define variables than it would be to
import them from a text file and that my use of this component is
wayward/errant. However, I don't know where the heck to put this stuff
if this is the wrong place.
>
> Further, I don't seem to be able to get the expected values when I
put these types of expressions in other components... UNLESS I put them
in the title. The ${__time(YMD)} works great if I put it in a COMPONENT
LABEL (ie.- I name that component "Today is ${__time(YMD)}" I'll see
"Today is 20080410" in the results), but doesn't want to do what I'm
expecting when I stick it anywhere else. That makes absolutely no sense
to me. How/what am I not understanding?
It should work almost anywhere.
>
> I'd greatly appreciate any guidance/ pointers/ references to anything
that'll help me accomplish this.
>
> Regards,
>
>
> - Dan
>
>
> __________________________________________________
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