mongoDB查询“WHERE _id>阈" [英] mongoDB query "WHERE _id > threshold"

问题描述

我怎么能有一个类似于SQL的mongo查询... WHERE _id>阈值

我试过以下，但它不给我任何结果。

  db.things.find（_id：{$ gt：someid}}）; 
  

这是因为_id字段有点特别，它的格式是？

  _id：{$ oid：someid} 
  

解决方案

比较像like

_id mongo中的键不是（默认情况下）一个字符串 - 它是一个mongo objectId。

您需要比较相同类型才能获得有意义的结果：

  oid = new ObjectId（）; 
 db.things.find（_id：{$ gt：oid}）; 
  

不读取mongoexport文件

Mongo导出文件如下所示：

  {_id：{$ oid：4f876b00c56da1fa6a000030}，... 
  

这是一个对象id的json表示。 Mongo不希望在实际查询数据库时使用这种语法。这是行不通的：

 ＃将不起作用
 db.things.find（_ id。$ oid： {$ gt：string}）; 
  

id作为字符串

如果您有一个字符串的id，你会这样：

  str =123456789012345678901234; 
 oid = new ObjectId（str）; 
 db.things.find（_id：{$ gt：oid}）; 
  

id作为部分字符串

如果你的字符串不是一个有效的oid（不是24个字符长），你只会从mongo得到一个异常，或者根据你的驱动程序得到一个新的oid。如果您有部分对象ID，则可以使用0填充以生成有效的oid，因此可以通过部分对象ID查找。例如：

  oid = new ObjectId（str +0000）; 
 db.things.find（_id：{$ gt：oid}）; 
  

How can I have a mongo query similar to the SQL "...WHERE _id > threshold"

I tried the following, but it doesn't give me any result.

 db.things.find(_id: {$gt: someid} });

Is it because the _id field is a little special, in that it has the format?

_id : {"$oid" : "someid"} 

解决方案

Compare like with like

The _id key in mongo is not (by default) a string - it is a mongo objectId.

You need to compare to the same type to get a meaningful result:

oid = new ObjectId();
db.things.find(_id: {$gt: oid});

Don't read mongoexport files

Mongo export files look like this:

{ "_id" : { "$oid" : "4f876b00c56da1fa6a000030" }, ...

This is a json representation of an object id. Mongo doesn't want you to use that kind of syntax when actually querying the db. This will not work:

# will not work
db.things.find("_id.$oid": {$gt: "string"});

id as a string

If you have the id as a string, you'd do:

str = "123456789012345678901234";
oid = new ObjectId(str);
db.things.find(_id: {$gt: oid});

id as a partial string

If the string you have is not a valid oid (not 24 chars long), you'll just get an exception from mongo - or depending on your driver, a new oid. If you have a partial object id you can pad with 0s to make a valid oid and therefore permit finding by partial object ids. e.g.:

oid = new ObjectId(str + "0000");
db.things.find(_id: {$gt: oid});

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