Apache-Nifi: A Short Description of ifElse
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Join For FreeI had been working with Apache-NiFi for last few months at my work. During this period I mostly used csv
-based operations.
Recently, I got a problem with the following scenario.
In my flowfile
, I needed to do a regex
operation on a column value and `replace` them with some other code. I did this easily using the replaceAll
function.
First, let's see what replaceAll
does in Apache-NiFi. It takes two string arguments, first one is a regex
and second is the replacement value.
For more details, I highly recommend reading Apache-NiFi expression language guide on replaceAll.
For the first attempt, I have used the following syntax for my column using UpdateRecord
processor :
xxxxxxxxxx
${field.value:replaceAll(${field.value:length():le(8)},'Undefined'):replaceAll('[a-z]+','Wrong')}
This first checks whether the length of the column value is less than 8 characters. If so, it replaces that with Undefined
. But some data matched with [a-z]+
pattern had been replaced with Wrong
, even though they are less than 8 characters.
I tried to solve this issue myself, and as I was taking too much time, I asked the StackOverflow community. Lamanus’s answer made me think about ifElse
in Apache-NiFi.
So now, let's go and see how Apache-NiFi’s ifElse
behaves. It takes two arguments, but the difference is that, its the result based on Subject
of the expression.
If the subject is true
then, first argument is evaluated else second.
As given in the example: ${bool:ifElse('a','b')}
, here bool
is true. So, if I use replaceAll
with this, the value will be replaced with a
.
In order to do my scenario using this, I had to change the logic by checking whether it has more than 8 characters and then applying my custom regex
based operations.
xxxxxxxxxx
${field.value:length():ge(8):ifElse(
${field.value:replaceAll(‘[a-z]+’,’Wrong’)
:replaceAll('[0-9][a-z]+','Variable1')
,${field.value:replace(${field.value},'Undefined')}
// this is the statement executed when value length is shorter than 8 characters.)}
I hope this short description will give you a better understanding how to use ifElse
in Apache-NiFi.
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