TypeError：无法读取null MongoDb错误的属性“长度”

Question

Getting a mongodb error on a query. Here the error:

TypeError: Cannot read property 'length' of null

Here's the code:

// Open a connection with MongoDB

MongoClient.connect(process.env.MONGO_URL, (error, db) => {
  let dbo = db.db('gamblenomore');

//Running a query to find all customers that are in timezone CST.

dbo.collection('customers').find({therapyConfirmation: true, therapyTimeZone: 'CST', therapyDay: { $gt: 0 } }).toArray((error, result) => {
    let max = result.length;
    if (error) {
      throw error;
    }

There are no documents currently in 'customers' with the above criteria.

Answer 1

Change your code to:

dbo.collection('customers').find({
  therapyConfirmation: true,
  therapyTimeZone: 'CST', 
  therapyDay: { $gt: 0 } 
}).toArray((error, result) => {
    if (error) {
      throw error;
    }
    let max = result.length;
    // some other code
});