在MongoDB上，当我的回调位于“查找"内部时，如何限制查询? [英] On MongoDB how can I limit the query, when my callback is inside "find"?

问题描述

我在MongoDB中有这个查询

I have this query in MongoDB

db.privateMessages.find( 
    { $or : [ 
       {fromId: userId, toId: socket.userId} , 
       {fromId: socket.userId, toId: userId} ] 
    }, 
    function(err, messages) { pushSvdMsgs(messages); });

除了我得到50个结果的事实之外，它都能完美运行.

It works perfectly, except for the fact that I get 50 results.

我已经尝试过了:

db.privateMessages.find( { $or : [ {fromId: userId, toId: socket.userId} , {fromId: socket.userId, toId: userId} ] }, function(err, messages) { pushSvdMsgs(messages); }).limit(10);

但这也无济于事，所以我在下面尝试了一下，但也无济于事.

But that didn't help either, so I tried this below which also didn't help limit it.

db.privateMessages.find( { $or : [ {fromId: userId, toId: socket.userId} , {fromId: socket.userId, toId: userId} ] }, { $limit : 2 }, function(err, messages) { pushSvdMsgs(messages); });

如何限制此查询的结果数量，并仍然以与我相同的方式调用回调?

How can I limit the number of results from this query, and still call the callback the same way I have?

推荐答案

您几乎完全正确.试试这个:

You got it almost right. Try this one:

db.privateMessages.find( { $or : [ {fromId: userId, toId: socket.userId} , 
                                   {fromId: socket.userId, toId: userId} ] },
                         {}, 
                         { limit : 2 }, 
                         function(err, messages) { pushSvdMsgs(messages); });

语法为find(query, fields, options).我们需要一个空对象来使驱动程序正确解释选项.

The syntax is find(query, fields, options). We need that empty object to make driver interpret options correctly.

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