How does koa transfer values between two middleware?

  mongodb, question

How to transfer values between two middleware'/', koaBody, function* (next) {
 var body = this.request.body;
 yield body;
 yield next;
 app.use(function* (next) {
 Log ("middleware 2");
 yield this.mongo.db('app_info').collection('platform').insert({"xiaoming":"xiaoming1"});
 this.body=  this.mongo.db('app_info').collection('platform').findOne();

As above, I want to transfer the body obtained from post of the first middleware to the second middleware, and then the second middleware will store it into monodb. How can I get it?

Global variable value transfer