路由函数如下：

    route.post('/readport',function *(){
	var postdata = yield parse(this);
	var dataproject = postdata["selectedpro"];

	var portname =[] ;
	yield portname;
	mysqlinsertp.selectport(dataproject,function(comerr,row){
		if(row.length == 0){
			console.log("没有信息");
		}
		else{
			for(var i = 0; i < row.length; i++){
				portname[i] = row[i].portname;
			}
			//var result = '{ "status": "200", "ok": "true", "data": "'+portname+'" }';
			//this.body = JSON.parse(result); //尝试在这里返回，但前台获取不到值
		}
	});
	yield portname;
	var result = '{ "status": "200", "ok": "true", "data": "'+portname+'" }';
	this.body = result;//在这里返回的话因为这里比上面函数先执行，所以portname的值为空
    });

请教怎么样可以把得到值的result赋值给this.body后返回给前端ajax请求

操作数据库函数声明如下：

    exports.selectport = function(projectname,callback){
    client.query('SELECT DISTINCT portname FROM invoketable where projectname =?',projectname, function(err, results) {
        var count = Object.keys(results).length;
        if(count == 0) {
            return ;
        }
        else{
            console.log(results);
            callback(null, results);
        }
    });
    }