Query json data on MongoDB

Question

I have a rather complex structure on my json and I cannot find how to query it to get the rows I am interested in. Here is a sample of my data:

{
    "_id" : ObjectId("5282bf9ce4b05216ca1b68f8"),
    "authorID" : ObjectId("5282a8c3e4b0d7f4f4d07b9a"),
    "blogID" : "7180831558698033600",
    "blogs" : {
        "$" : {
            "posts" : [
                [
                    {
                        "author" : {
                            "displayName" : "mms",
                            ...
                            ...
                            ...
}}}

So, I am interested in finding all json entries that have the author displayName equal to "mms".

My collection name is bz so, a find all query would be: db.dz.find()

What criteria do I have to put inside the find() to only get json document with author displayName equal to mms?

Any ideas?

Thank you in advance!

Not just not recommended, it's not allowed or supported. docs.mongodb.org/manual/reference/limits/… — JohnnyHK
– JohnnyHK, Commented Sep 18, 2014 at 2:04
@JohnnyHK, Thanks for your information. Now I see that V2.6 rejects it even on update operation. By the way, the manual's description is not precise enough. $ is allowed in field name but not as the first character. — Wizard
– Wizard, Commented Sep 18, 2014 at 2:51
Well, this query works for me: db.dz.find({"blogs.$.cat" : "red"}) So, in this case $ works a field name. — pappus
– pappus, Commented Sep 19, 2014 at 14:11
Your problem will be, that $ is a "placeholder" character in a Mongo query. It means, "this item you've found matching the criteria". This will make your queries confusing when you eventually need one that uses the $ operator/helper. It will not mean what you think it means. — Simon Whitehead
– Simon Whitehead, Commented Sep 21, 2014 at 13:14

Wizard · Accepted Answer · 2014-09-18 03:54:54Z

1

Suppose you have replaced field name "$" with "dollarSign".

Then db.dz.find({"blogs.dollarSign.posts.author.displayName": "mms"}) will fetch whole documents according to your requirements.

answered Sep 18, 2014 at 3:54

Wizard

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1 Comment

pappus Over a year ago

I tried this. It does not throw an exception but it does not bring back any result either. I have not replaces the $ field because as I write in my previous comment this does not cause any problems in my case.

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