Iterate a Cursor in the mongo Shell在mongo Shell中迭代游标¶

Manually Iterate the Cursor手动迭代游标¶

In the mongo shell, when you assign the cursor returned from the find() method to a variable using the var keyword, the cursor does not automatically iterate.在mongo shell中，当使用var关键字将find()方法返回的游标分配给变量时，游标不会自动迭代。

You can call the cursor variable in the shell to iterate up to 20 times [1] and print the matching documents, as in the following example:您可以在shell中调用游标变量来迭代多达20次[1]，并打印匹配的文档，如下例所示：

var myCursor = db.users.find( { type: 2 } );

myCursor

You can also use the cursor method next() to access the documents, as in the following example:您还可以使用游标方法next()访问文档，如下例所示：

var myCursor = db.users.find( { type: 2 } );

while (myCursor.hasNext()) {
   print(tojson(myCursor.next()));
}

As an alternative print operation, consider the printjson() helper method to replace print(tojson()):作为另一种打印操作，请考虑用printjson()辅助方法来代替print(tojson())：

var myCursor = db.users.find( { type: 2 } );

while (myCursor.hasNext()) {
   printjson(myCursor.next());
}

You can use the cursor method forEach() to iterate the cursor and access the documents, as in the following example:您可以使用游标方法forEach()迭代游标并访问文档，如下例所示：

var myCursor =  db.users.find( { type: 2 } );

myCursor.forEach(printjson);

See JavaScript cursor methods and your driver documentation for more information on cursor methods.有关游标方法的更多信息，请参阅JavaScript游标方法和驱动程序文档。

Iterator Index迭代器索引¶

In the mongo shell, you can use the toArray() method to iterate the cursor and return the documents in an array, as in the following:在mongo shell中，您可以使用toArray()方法迭代游标并返回数组中的文档，如下所示：

var myCursor = db.inventory.find( { type: 2 } );
var documentArray = myCursor.toArray();
var myDocument = documentArray[3];

The toArray() method loads into RAM all documents returned by the cursor; the toArray() method exhausts the cursor.toArray()方法将游标返回的所有文档加载到RAM中；toArray()方法将耗尽游标。

Additionally, some drivers provide access to the documents by using an index on the cursor (i.e. cursor[index]). 此外，一些驱动程序通过使用游标上的索引（即cursor[index]）提供对文档的访问。This is a shortcut for first calling the toArray() method and then using an index on the resulting array.这是一个快捷方式，用于首先调用toArray()方法，然后对生成的数组使用索引。

Consider the following example:考虑下面的例子：

var myCursor = db.users.find( { type: 2 } );
var myDocument = myCursor[1];

The myCursor[1] is equivalent to the following example:myCursor[1]相当于以下示例：

myCursor.toArray() [1];

Cursor Behaviors游标行为¶

var myCursor = db.users.find().noCursorTimeout();

var myCursor = db.inventory.find();

var myFirstDocument = myCursor.hasNext() ? myCursor.next() : null;

myCursor.objsLeftInBatch();

Cursor Information游标信息¶

The db.serverStatus() method returns a document that includes a metrics field. db.serverStatus()方法返回一个包含metrics字段的文档。The metrics field contains a metrics.cursor field with the following information:metrics字段包含一个metrics.cursor字段，其中包含以下信息：

• number of timed out cursors since the last server restart自上次服务器重新启动以来超时的游标数
• number of open cursors with the option DBQuery.Option.noTimeout set to prevent timeout after a period of inactivity设置选项DBQuery.Option.noTimeout以防止在一段不活动时间后超时的打开游标数
• number of “pinned” open cursors“固定”打开游标的数量
• total number of open cursors打开的游标总数

Consider the following example which calls the db.serverStatus() method and accesses the metrics field from the results and then the cursor field from the metrics field:考虑下面的示例，调用db.serverStatus()方法，从结果中访问度量字段，然后从度量字段访问游标字段：

db.serverStatus().metrics.cursor

The result is the following document:结果是以下文件：

{
   "timedOut" : <number>
   "open" : {
      "noTimeout" : <number>,
      "pinned" : <number>,
      "total" : <number>
   }
}