Synapse snack - Increment counter variable

Case
I want to increment a variable to count some actions. For example to break a until loop after 4 times. What is the Synapse (or ADF) equivalent of counter++ or counter = counter + 1 because you can not self reference in a variable expression.

The expression contains self referencing variable.
A variable cannot reference itself in the expression.

Solution
Unfortunately you can not self reference a variable in an expression of a Set variable activity. If you want to increment a variable called Counter then you can't use an expresion like this:

@add(int(variables('Counter')), 1)

1) Add extra variable
The trick is to use two variables (and two Set Variable activities). In this example we have besides the Counter variable also a second 'helper' variable called NewCounterValue. The type is String for both since there isn't an integer type available.

Two variables to increment a variable value

2) Add first Set variable

Now add two Set variable activities to the canvas of your pipeline. In this case inside an UNTIL loop. The first activity will set the value of the helper variable called NewCounterValue. It retrieves the value of the original Counter variable, converts it to an Integer and then adds 1. After that it is converted back to a String:

@string(
    add(
        int(variables('Counter')),
        1
    )
)

Increment variable part 1

3) Add second Set variable

The second activity just retrieves the value of the new helper variable and uses it to set the value of the Counter variable. No need to cast the variable to an other type.

Increment variable part 2

4) Until loop

Now lets test it in an until loop where it stops the until loop after 4 times.

The Until loop

The Until loop in action

Conclusions

In this post we showed you how to overcome a little shortcoming in Synapse and ADF. It's a handy contruction to do something max X times. For example checking the status max 4 times. The Until stops whenever the status changes or when the retry counter is 4 or higher.

@or(
    greaterOrEquals(int(variables('Counter')),4)
,   not(equals(activity('WEB_Check_Status').output.status,'PENDING'))
)

Case Example for retry