salix/modules/entry/back/models/entry-dms.js

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

module.exports = Self => {
    require('../methods/entry-dms/removeFile')(Self);
    require('../methods/entry-dms/downloadFile')(Self);
    require('../methods/entry-dms/uploadFile')(Self);

    Self.rewriteDbError(function(err) {
        if (err.code === 'ER_DUP_ENTRY')
            return new UserError('This document already exists on this entry');
        return err;
    });
};