“合并"查看整理到CouchDB中有用的输出 [英] "merge" view collation into useful output in CouchDB

问题描述

在CouchDB中执行"join" 时，可以使用视图排序规则将记录分组在一起.例如，有两个文档类型 customers 和 orders .这样您就可以返回客户，然后返回该客户的所有订单，然后返回下一个客户和订单.

When doing a "join" in CouchDB, you can use view collation to group the records together. For example, having two document types customers and orders. So that you can return customer, then all the orders for that customer, then the next customer, and orders.

问题是，如何合并行，以便如果您有10个客户和40个订单，则输出仍然是10行而不是50行.您实质上是在 customer 行.

The question is, how do you do a merging of rows, so that if you have 10 customers, and 40 orders, your output is still 10 rows instead of 50. You essentially add more information into your customer row.

我相信使用_list或reduce将解决此问题.问题是如何精确地做到这一点?

I believe using a _list or a reduce will solve this. The question is how exactly to do this?

推荐答案

我第二次

I second jhs answer, but I think his "Option 2" is too dangerous. I learned it the hard way. You can use reduce function for many nice things like getting the last post of each user of a blog, but you cannot use it for anything which does not reduce the amount of data returned.

为了提供事实依据，我编写了这个小脚本来生成200个客户，每个客户20个订单.

To support it with facts, I made this little script to generate 200 customers with 20 orders each.

#!/bin/bash
echo '{"docs":['
for i in $(seq 1 200); do
  id=customer/$i
  echo '{"_id":"'$id'","type":"customer","name":"Customer '$i'"},'
  for o in $(seq 1 20); do
    echo '{"type":"order","_id":"order/'$i'/'$o'", "for":"'$id'", "desc":"Desc '$i$o'"},'
  done
done
echo ']}'

这是非常可能的情况，足以抛出Error: reduce_overflow_error.

It is a very likely scenario and it is enough to throw a Error: reduce_overflow_error.

恕我直言，您有两个选择:

IMHO the two option you have are:

选项1:优化列表功能

只需做一些工作，您就可以手动构建JSON响应，这样就无需在数组中累积订单.

With a little bit of work, you can build the JSON response by hand, so that you do not need to accumulate orders in an array.

我已经编辑了jhs的列表功能，以避免使用数组，因此您可以让客户拥有任意数量的订单.

I have edited the list function of jhs to avoid any use of arrays, so you can have customers with any number of orders.

function(head, req) {
  start({'headers':{'Content-Type':'application/json'}});

  var first_customer = true
    , first_order = true
    , row
    ;

  send('{"rows":[');

  while(row = getRow()) {
    if(row.key[1] === 2) {
      // Order for customer
      if (first_order) {
        first_order = false;
      } else {
        send(',');
      }
      send(JSON.stringify(row.value));
    }
    else if (row.key[1] === 1) {
      // New customer
      if (first_customer) {
        first_customer = false;
      } else {
        send(']},');
      }
      send('{"customer":');
      send(JSON.stringify(row.key[0]));
      send(',"orders":[');
      first_order = true;
    }
  }
  if (!first_customer)
    send(']}');

  send('\n]}');
}

选项2:针对您的用例优化文档

如果您确实需要将订单包含在同一文档中，请问问自己是否可以这种方式存储，并避免在查询时进行任何处理.

If you really need to have the orders in the same document, then ask yourself if you can store it this way and avoid any processing while querying.

换句话说:尝试充分利用文档数据库提供的可能性.设计文档以使其最适合您的用例，并减少使用它们所需的后处理.

In other words: try to fully exploit the possibilities offered by a document database. Design the documents to best fit your use case, and reduce the post-processing needed to use them.

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