NodeJS/MongoDB:对数组字段执行切片操作 [英] NodeJS/MongoDB: Perform Slice operation on an array field

问题描述

我在尝试对数组执行切片时遇到了困难我有一个名为 comments 的集合，每个文档都有一个数组字段，我想访问它并应用切片进行分页，请帮忙！！尝试了 monk 和 mongodb 不好

I am having a tough time trying to execute a slice on an array I have a collection called comments, each document has an array field, i want to access it and apply slice for paging purpose please help !! tried monk and mongodb no good

示例:

 {  
   _id:xyz,
   msgs:[{.....},{.....},{.....}]
 }


database.collection("comments")
  .find({"_id": id},{ "msgs": { "$slice": [2,5] } })
  .toArray( function(err, result){
        //implementation
   });

推荐答案

对于 mongodb 驱动程序:

For mongodb Driver:

代替

.find({"_id": id},{ "msgs": { "$slice": [2,5] } })

使用

.find({"_id": id}).project({ "msgs": { "$slice": [2,5] } })

如给定此处$slice 运算符属于 投影 类型.NodeJS 的 mongodb 驱动程序需要调用额外的 .project 函数来投影选择性字段以及使用投影运算符.

As given here the $slice operator is of Projection type. The mongodb driver for NodeJS needs call to an extra .project function to project selective fields as well as to use projection operators.

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