findOneAndUpdate

[Lasse_Johansen]

How can I findOneAndUpdate with an expression of
{$expr: { $lt: [{ $size: “$users” }, “package.maxUserCount”] }}

I want to update a document where users array size is less than maxUserCount.

It does not work, somehow it returns true on any document

[Lasse_Johansen]

{$expr: { $lt: [{ $size: “$users” }, “$package.maxUserCount”] }}

[NestorDaza (Néstor)]

Hello Lasse, assuming your maxUserCount is 20, you could do something like this:

db.<<<yourCollection>>>.findOneAndUpdate({'users.20': {$exists: false}}, {'$set' : {<<yourProperty>>: <<newValue>>}});

[steevej (Steeve Juneau)]

I had this post in my bookmark but was clueless until

@NestorDaza

assuming your maxUserCount is 20

and

@NestorDaza

{'users.20': {$exists: false}}

I think that this is the difficulty about this one.

The maxUserCount cannot be assumed since it is the value of another field of the source document.

But

@NestorDaza

{'users.20': {$exists: false}}

is the key and leads me to a variation where 20 is not assumed but taken from another field.

{ "$expr" : {
    "$eq" : [
         { $type : { $arrayElemAt : [ "$users" , "$package.maxUserCount" ] } } ,
         "missing"
    ]
} }

[steevej (Steeve Juneau)]

Congratulations for your new position at MongoDB.

[NestorDaza (Néstor)]

@steevej

{ "$expr" : {
    "$eq" : [
         { $type : { $arrayElemAt : [ "$users" , "$package.maxUserCount" ] } } ,
         "missing"
    ]
} }

That works beautifully

[steevej (Steeve Juneau)]

@NestorDaza

That works beautifully

But but. I returned to the original post and original query. And it also works wonderfully. Yes the following

@Lasse_Johansen

{"$expr" : { "$lt": [{ "$size": "$users" }, "$package.maxUserCount"] }}

So I felt in the same trap I felt before, that is, assuming that there was a real problem other than typos in field names and/or missing $ in some field names. In the first post, package.maxUserCount was missing the $ but that was corrected promptly. I should also have requested sample documents. Perhaps the discrepancy is between the field name

@Lasse_Johansen

package.maxUserCount

or the text requirement

@Lasse_Johansen

users array size is less than maxUserCount

I tried different typos variations and the one that

@Lasse_Johansen

returns true on any document

is the one where the $ sign is missing in front of package.maxUserCount. When the dollar sign is present with a non existing field name the query is false for all documents.

[steevej (Steeve Juneau)]

@Lasse_Johansen, it has been 5 days since you have received valuable replies to your original post.

We and all readers would appreciate a followup. Perhaps even closure by marking one of the post as the solution in case your issue was addressed correctly. And I think it was.

Thanks in advance

[Lasse_Johansen]

Sorry for the late reply.

My 2nd post was actually the answer to my question. Adding the dollar sign made the query work.

Do I need to mark any of the answers as the correct answer, or how do one proceed to finish up a question?

[steevej (Steeve Juneau)]

You could certainly mark your second post as the answer but it lacks some information.

The missing $ as the possible cause was mentioned in the post

@steevej

the $ sign is missing in front of package.maxUserCount

You decide which posts is more useful to the community and mark it as the solution.