Microsoft Flow – Improve your switch case with coalesce

One of the steps in Microsoft Flow can cause a lot of failures and it might not always be clear why things are going wrong. In this post I’m going to have a look at the Switch.

I created a list with a choice field. The field is not mandatory and therefore it could be left blank. I then created my flow that triggers on the creation of a new item and a switch that responds to my choice field.

then I created a new list item and selected Choice 1 as my value for my choice field.

All good so far, but now what happens if you don’t select anything and the choice field remains empty. You might expect (or hope) that the default branch is followed.

 

But that is not the case. Your flow will fail with an ugly:

The execution of template action ‘Switch’ failed: The result of the evaluation of ‘scope’ action expression ‘@triggerBody()?[‘Choice’]?[‘Value’]’ is not valid. It is of type ‘Null’ but is expected to be a value of type ‘String, Integer’.

 

One way to get around this is to check before the switch if the choice field has been set or not and then run the switch only when it is set. If this is your approach then “have you noticed that your flows become large?”

There is a better way around this.

Within the switch don’t use the Choice Value, but use the Choice value inside a coalesce function:

[code lang=text]
coalesce(triggerBody()?[‘Choice’]?[‘Value’],’Unknown’)
[/code]

The Coalesce function will return either the value of the Choice or if that is not set, ‘Unknown’ will be returned.

And now your flow runs without failure (Well at least your switch doesn’t fall over!)

 

 

 

Coalesce in switch Case
Comments ( 5 )
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  • Miguel

    I’m working for HR and I just wanted to say BIG/HUGE THANKS! this has helped me enormously to keep my flow working without that ‘Null’ error message. 🙂

  • Michelle S

    Can you do this with a boolean response? I tried this, it pushes through an unknown response every time.

    • Pieter Veenstra – UK – Business Applications and Office Apps & Services Microsoft MVP working as a Senior Consultant at Triad Group Plc. You can contact me using contact@veenstra.me.uk.
      Pieter Veenstra

      Hi Michelle,

      Yes you can use boolean values in select statements. Can you email me a screenshot of your select?

  • Andrew

    Was just looking for this , you saved my bacon again thanks Pieter !