两个中间件之间如何传值呢

test.post('/', koaBody, function* (next) {
    var body = this.request.body;
    console.log(body);
    yield body;
    yield next;
})
app.use(function* (next) {

  this.body="sucessful";
  console.log("中间件2");
  yield this.mongo.db('app_info').collection('platform').insert({"xiaoming":"xiaoming1"});
  this.body=  this.mongo.db('app_info').collection('platform').findOne();
});

如上，我想把第一个中间件的post获取的body，传入第二个中间件中，然后由第二个中间件存入monodb。请问我应该如何获取？