How to select only one from the manage list in belongs to many (with Pivot Data)

[as7-ali-soltani]

How to select only one from the manage list when showCheckboxes: false or checked only one when showCheckboxes: true in backend controller with belongs to many (with Pivot Data) relation.
no pivot form and extra fields defined in pivot table.
example:

user:
-id
-name

role:
-id
-name

user_role:
-user_id
-role_id