Get `Use of expired sessions is not permitted` error when using client session on mongodb nodejs application

Question

My mongodb is 3.6 and my nodejs application is using mongo client 3.0. Below is the source code to use mongo client session to ensure causal relationship:

const session = client.startSession();
  const col = client.db('test').collection('test');
  col
    .insert({a: true}, {w: 0, j: false, session})
    .then(() => {
      return col.count({session});
    })
    .then(ret => {
      console.log(ret);
    }).catch(err => console.error(err));
  session.endSession();
}

I got below errors when running this application. It works without specifying the session for the insert or count command. I wonder how I can use session in this case.

    { MongoError: Use of expired sessions is not permitted
    at executeOperation (/Users/joey/dev/mongodb/demo/node_modules/mongodb/lib/utils.js:390:13)
    at Collection.count (/Users/joey/dev/mongodb/demo/node_modules/mongodb/lib/collection.js:1889:10)
    at col.insert.then (/Users/joey/dev/mongodb/demo/index.js:33:18)
    at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:188:7)
  name: 'MongoError',
  message: 'Use of expired sessions is not permitted' }

Answer 1

I think I found out what wrong with my code. I need to move session.endSession(); to the then or catch since it is a promise call.