Required field Validation

I have 3 fields say A,B,C in the page based on the value selected in the A & B need to decide whether C is required field or not . This is achieved by 1. custom expression on the field C [In the type need to write conditions] 2. validating in the microflow  Which of the approach is performance wise better?  
1 answers

hi Karthiha

custom Expressions will be trigger on Page refresh as well. so if you have any onchange on any of the other fields this will be triggered. 

also its not an easy task to add such a custom validation. 

Adding NanoFlow or Microflow validation is always preferred.  Since its just 1 Field validation Performance is not delayed by adding this.