javascript - 如何使用 mongojs 遍历整个 MongoDB 集合？

Question

我正在使用 mongojs，我正在尝试遍历集合中的所有元素

index = 0

db.keys.find({}, {uid: 1, _id: 0}).forEach((err, key) =>
    if err?
        console.log err
    else 
        console.log (++index) + " key: " + key_uid

哪些日志

1 key: bB0KN
2 key: LOtOL
3 key: 51xJM
4 key: x9wFP
5 key: hcJKP
6 key: QZxnE
.
.
.
96 key: EeW6E
97 key: wqfmM
98 key: LIGHK
99 key: bjWTI
100 key: 2zNGE
101 key: F71mL

然后停止。但是，当我从终端登录 mongo 并运行时

> db.keys.count()
2317381

很明显它应该返回更多的键。您有什么想法可能导致这种行为吗？

Answer 1

您需要使用 each() 方法，而不是 forEach()。 forEach() 将遍历批处理中的每个文档 - 正如您发现的那样，默认值为 101。each() 将遍历光标中的每个文档。来自文档:

each

Iterates over all the documents for this cursor. As with {cursor.toArray}, not all of the elements will be iterated if this cursor had been previouly accessed. In that case, {cursor.rewind} can be used to reset the cursor. However, unlike {cursor.toArray}, the cursor will only hold a maximum of batch size elements at any given time if batch size is specified. Otherwise, the caller is responsible for making sure that the entire result can fit the memory.

http://mongodb.github.io/node-mongodb-native/api-generated/cursor.html

示例代码:

// Grab a cursor
      var cursor = collection.find();

      // Execute the each command, triggers for each document
      cursor.each(function(err, item) {

        // If the item is null then the cursor is exhausted/empty and closed
        if(item == null) {

          // Show that the cursor is closed
          cursor.toArray(function(err, items) {
            assert.ok(err != null);

            // Let's close the db
            db.close();
          });
        };
      });