MongoDB: How to query for records where field is n

问题:

I have an Email document which has a sent_at date field:

{
  'sent_at': Date( 1336776254000 )
}

If this Email has not been sent, the sent_at field is either null, or non-existant.

I need to get the count of all sent/unsent Emails. I'm stuck at trying to figure out the right way to query for this information. I think this is the right way to get the sent count:

db.emails.count({sent_at: {$ne: null}})

But how should I get the count of the ones that aren't sent?

回答1:

If the sent_at field is not there when its not set then:

db.emails.count({sent_at: {$exists: false}})

If its there and null, or not there at all:

db.emails.count({sent_at: null})

Refer here for querying and null

回答2:

If you want to ONLY count the documents with sent_at defined with a value of null (don't count the documents with sent_at not set):

db.emails.count({sent_at: { $type: 10 }})

回答3:

Use:

db.emails.count({sent_at: null})

Which counts all emails whose sent_at property is null or is not set. The above query is same as below.

db.emails.count($or: [
  {sent_at: {$exists: false}},
  {sent_at: null}
])

回答4:

Seems you can just do single line:

{ "sent_at": null }