How to compare previous effective date with current effective date of specific action code

Summary:

We've requirement to throw an error when line manager trying to extend secondment after 1 year then error should be thrown.

Content (please ensure you mask any confidential information):

Object validation error if LM use Extend Secondment action code which is greater than 1 year from previous secondment date

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Code Snippet (add any code snippets that support your topic, if applicable):