salix/modules/supplier/back/models/supplier-agency-term.js

const UserError = require('vn-loopback/util/user-error');

module.exports = Self => {
    Self.rewriteDbError(function(err) {
        if (err.code === 'ER_DUP_ENTRY')
            return new UserError(`The agency is already assigned to another autonomous`);
        return err;
    });
};