使用c-driver通过索引更新mongo数组元素 [英] Update mongo array elements by index with c-driver

问题描述

要更新mongo数组的元素，我使用的语法如下:

To update elements of a mongo array, I was using syntax like:

{"$set":{"a.0":1238},{"a.1":402}}

或者，更准确地说，我正在使用我认为与之等效的C驱动程序函数调用.这似乎工作正常，但是当我在MongoHub中查看该对象时，我看到:

Or, more accurately, I was using the C-driver function calls that I think are equivalent to that. This seemed to work fine, but when I look at the object in MongoHub, I see:

a: {"0":1238,"1":402}

代替:

a: [1238,402]

有人知道使用C驱动程序通过索引访问数组元素的正确语法是什么吗?我现在正在做的事情符合我的近期目标，但是我不确定性能是否存在重大差异.另外，以后可能需要使用需要真实数组的操作.

Does anyone know what is proper syntax to access array elements by index with C-driver? What I am doing now serves my immediate purpose, but I am not sure if there are significant performance differences. Also, I might later need to use operations that require true array.

推荐答案

如果字段不存在，则此点符号查询会将其创建为哈希(对象)，并将值分配给该哈希的键.如果field存在并且是一个数组，它将表现出预期的效果.观看本次会议.

If a field didn't exist, then this dot-notation query will create it as a hash (object) and assign values to keys of that hash. If field exists and is an array, it will behave as you expect. See this session.

> db.arrays.insert({});
> db.arrays.find();
{ "_id" : ObjectId("4f518c8b58713e4dbadbfb9f") }
> db.arrays.update({ "_id" : ObjectId("4f518c8b58713e4dbadbfb9f") }, {$set: {"a.0": 123}});
> db.arrays.find();
{ "_id" : ObjectId("4f518c8b58713e4dbadbfb9f"), "a" : { "0" : 123 } }


> db.arrays.insert({a: []})
> db.arrays.find();
{ "_id" : ObjectId("4f518c8b58713e4dbadbfb9f"), "a" : { "0" : 123 } }
{ "_id" : ObjectId("4f518cca58713e4dbadbfba0"), "a" : [ ] }
> db.arrays.update({ "_id" : ObjectId("4f518cca58713e4dbadbfba0") }, {$set: {"a.0": 123}});
> db.arrays.find();
{ "_id" : ObjectId("4f518c8b58713e4dbadbfb9f"), "a" : { "0" : 123 } }
{ "_id" : ObjectId("4f518cca58713e4dbadbfba0"), "a" : [ 123 ] }

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