如何使用 MongoDB Node.js Driver Cursor 和 AggregateCursor 进行管道传输? [英] How to pipe with MongoDB Node.js Driver Cursor and AggregateCursor?

问题描述

不确定使用 MongoDB Node.js Drive 3.0.根据 docs，Cursor::pipe 和 AggregateCursor::pipe 接收可写流，因此您似乎应该能够执行以下操作:

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);

但结果是抛出错误:

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

这行得通，但对我来说感觉有点麻烦，不适合管道链接.

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 );
    });

有没有办法使用适用于 Node.js 的 MongoDB 驱动程序创建标准管道链?

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

推荐答案

看来错误是我试图将 objectMode 中的流通过管道传输到 objectMode<中的流的结果/代码>.这是一个解决方案:

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);

您也可以扩展 stream.Writable 并将其设置为 objectMode，但以上似乎是最简单的解决方案.

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

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