uniqueness on custom field between bugs not closed

[duwil]

I need to validate a custom field that must be unique between the open issues, I mean that when you cannot open a new issue if there is already another issue not closed that has the same value in that custom field. Is that possible?

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[jb_mantis]

This is not possible out of the box and would require custom code. You would need to find the function that is called when someone tries to submit a new bug and you would need to add a function call to it that will check the submitted custom field value and see if there are any unclosed issues that already have that same value, and if so, cause the submission to fail. Not sure where to point you to start as I don't do custom coding in Mantis.