How to pipe with MongoDB Node.js Driver Cursor and AggregateCursor?

Question

Not sure of the proper way to pipe query results using MongoDB Node.js Drive 3.0. According to the docs, Cursor::pipe and AggregateCursor::pipe receive a Writeable streams so it seems like you should be able to do something like this:

collection.find(query).pipe(process.stdout);
collection.aggregate(query).pipe(process.stdout);

But it turns out to throw an error:

TypeError: Invalid data, chunk must be a string or buffer, not object

This works but it feels a little cumbersome to me doesn't lend itself to pipe chaining.

collection.find(query)
    .on('data', function(chunk) {
        buffer = Buffer.from(JSON.stringify(chunk))
        process.stdout.write( buffer );
    });


collection.aggregate(query)
    .on('data', function(chunk) {
        buffer = Buffer.from(JSON.stringify(chunk))
        process.stdout.write( buffer );
    });

Is there a way to do a standard pipe chain with with the MongoDB Driver for Node.js?

score 3 · Accepted Answer · answered Apr 13 '18 at 00:11

It appears the error was the result of my trying to pipe a stream in objectMode to a stream not in objectMode. Here is a solution:

collection.find(query)
    .stream({
        transform: function(chunk) {
            return JSON.stringify(chunk);
        }
    }).pipe(process.stdout);

collection.aggregate(query)
    .stream({
        transform: function(chunk) {
            return JSON.stringify(chunk);
        }
    }).pipe(process.stdout);

You could also extend stream.Writable and set it to objectMode, but the above seems like the simplest solution.

How to pipe with MongoDB Node.js Driver Cursor and AggregateCursor?

1 Answers1

Linked