Is it possible to check if there is another document in Meteor js cursor and

Question

Is it possible to check if there is another document in Meteor js cursor and

challenge

Currently, I am facing a complex issue with a large find query that needs to be halted based on specific conditions set on my server using "javascript". The goal is to optimize the process by streaming data from MongoDB in an iterative manner, retrieving results as needed without overwhelming the server or database.

desired outcome

Begin query and obtain cursor (r = Collection.find())
Check for next result (r.hasNext())
Retrieve next result (r.next())
Stop processing once criteria are met (delete r)

sample code snippet

Collection.find().forEach(function(doc) {
  doc = do_my_business(doc);
  if (doc.found) {
    // Stop processing and release the cursor
    return false;
  }
});

underlying issue

This question arose from a previous inquiry regarding efficient querying methods in MongoDB:

javascript mongodb meteor

Answer 1

Answer №1

A meteor cursor differs from a mongo cursor in that it lacks hasNext or next functionalities. Thus, the focus here is on utilizing forEach, which aligns with ES5 standards. Here are some approaches you can take:

1. Retrieve all documents into an array and iterate over them using a for loop, stopping when the desired criteria is met.

2. Set a flag when the criteria is satisfied and check this flag at the start of the function:

if (isSatisfied) return;
doc = process_document( doc );
if (doc.found) isSatisfied = true;

3. Implement a try-catch block:

foo = {};
try {
  Collection.find().forEach(function(doc) {
    doc = process_document( doc );
    if (doc.found) {
      throw foo;
    }
  });
} catch(e) {
  if (e !== foo) {
    throw e;
  }
}

4. Avoid using forEach and opt for $where with findOne instead. Consider running a find().limit(1).explain() to demonstrate that not every document will be accessed.

5. Store relevant data in your database to prevent the need for javascript operations on the cursor. It's best to steer clear of performing javascript loops on each document server-side, as storage costs less than processing power.

Answer 2

A meteor cursor differs from a mongo cursor in that it lacks hasNext or next functionalities. Thus, the focus here is on utilizing forEach, which aligns with ES5 standards. Here are some approaches you can take:

1. Retrieve all documents into an array and iterate over them using a for loop, stopping when the desired criteria is met.

2. Set a flag when the criteria is satisfied and check this flag at the start of the function:

if (isSatisfied) return;
doc = process_document( doc );
if (doc.found) isSatisfied = true;

3. Implement a try-catch block:

foo = {};
try {
  Collection.find().forEach(function(doc) {
    doc = process_document( doc );
    if (doc.found) {
      throw foo;
    }
  });
} catch(e) {
  if (e !== foo) {
    throw e;
  }
}

4. Avoid using forEach and opt for $where with findOne instead. Consider running a find().limit(1).explain() to demonstrate that not every document will be accessed.

5. Store relevant data in your database to prevent the need for javascript operations on the cursor. It's best to steer clear of performing javascript loops on each document server-side, as storage costs less than processing power.

Is it possible to check if there is another document in Meteor js cursor and

challenge

desired outcome

sample code snippet

underlying issue

Answer №1

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