问题描述
假设我有一个查询，该查询将返回非常大的响应.可能有成千上万条记录，甚至可能有数千兆字节的数据.
Let's say I have a query that is going to return a very large response. Possibly thousands of records and possibly gigabytes of data.
通常，在用户界面中，我们只显示此数据的一页.现在，我需要一个选项来获取整个结果集并将其流式传输到文件中.然后，用户可以随意下载此文件.
Normally in the UI, we just show a single page of this data. Now I need an option to take the entire result set and stream it out to a file. Then the user can go download this at their leisure.
那么我该如何使用查询生成器从查询中选择所有结果，然后将其分块流式传输到文件中而又不会耗尽内存?
So how do I select all results from a query using query builder and then stream it out to a file in chunks without running out of memory?
推荐答案
如果需要文档描述符，则可以打开对象流，如以下示例所示:
If you want the document descriptors, you can open an object stream as in the following example:
https://github.com. com/marklogic/node-client-api/blob/develop/examples/query-builder.js#L38
如果只需要文档的内容，则可以使用分块流，如以下示例所示(可以将相同的方法用于查询):
If you only want the content of the documents, you can use a chunked stream as shown in the following example (the same approach can be used for a query):
https://github.com. com/marklogic/node-client-api/blob/develop/examples/read-stream.js#L27
一般方法如下:
- 以写流的形式打开目标文件
https://nodejs.org/api/fs.html#fs_fs_createwritestream_path_options
- 查询文档的第一页，将文档的读取流传输到文件的写入流，注意将end选项设置为false:
https://nodejs.org/api/stream.html#stream_可读_pipe_destination_options
-
循环阅读文档，将起始页面增加页面长度，直到完成阅读
loop on reading documents, incrementing the start page by the page length until finished reading
在写入流上调用end()以关闭文件
call end() on the write stream to close the file
https://nodejs.org/api/stream.html#stream_writable_end_chunk_encoding_callback
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