mongodb update $in array fail when value duplicate

Question

I want to update sth together, allow operation on the same document more than once

for example, $inc 'csize' column X times if document's _id appear X times

but mongodb only work for once, how to do deal with this ?

or other solutions without $in ?

> db.user_info.findOne({_id:ObjectId("54bcc154ed9c800af1d11b47")})
{
        "_id" : ObjectId("54bcc154ed9c800af1d11b47"),
        "atime" : ISODate("2015-04-03T07:10:24.118Z"),
        "csize" : 25
}
> db.user_info.update({_id:{$in:[
        ObjectId("54bcc154ed9c800af1d11b45"),
        ObjectId("54bcc154ed9c800af1d11b45"),
        ObjectId("54bcc154ed9c800af1d11b46"),
        ObjectId("54bcc154ed9c800af1d11b47"),
        ObjectId("54bcc154ed9c800af1d11b47"),
        ObjectId("54bcc154ed9c800af1d11b47")
    ]}},
    {$inc: {csize:1}},
    true,
    true
)

> db.user_info.findOne({_id:ObjectId("54bcc154ed9c800af1d11b47")})
{
        "_id" : ObjectId("54bcc154ed9c800af1d11b47"),
        "atime" : ISODate("2015-04-03T07:10:24.118Z"),
        "csize" : 26
}

you see, 54bcc154ed9c800af1d11b47's csize only inc one time, instead of 3 times

chridam · Accepted Answer · 2015-04-03 09:15:27Z

1

No need to do an $in operation in your query thrice, just increase the field by the specific value you want (in your case it's 3) because the $inc operator accepts positive and negative values.

db.user_info.update(
   { 
       "_id" : ObjectId("54bcc154ed9c800af1d11b47") 
   },
   { 
       "$inc": { "csize": 3 } 
   }
)

answered Apr 3, 2015 at 9:15

chridam

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1 Comment

Ganiks Over a year ago

sorry, my example not illustrate my intension clearly, give you another example(I'll edit my question)

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