Filtter by array data in mongodb

Question

I have a mongodb data base like this:

{
    "_id" : ObjectId("530d24150fef5d9b065909ca"),
    "data" : "object 1",
    "my_array" : [
        {"arraydata" : "1"},
        {"arraydata" : "2"}
    ]
}
{
    "_id" : ObjectId("530d24150fef5d9b065909ca"),
    "data" : "object 2",
}
{
    "_id" : ObjectId("530d24150fef5d9b065909ca"),
    "data" : "object 3",
    "my_array" : [{"arraydata" : "1"}]
}

I want to make a query which only returns document that contains some data in my_array, in this case it'd returned the first and the last one.

I understood that $where statement is slow, so I want to get a better approach.

Thanks in advance.

possible duplicate of Why does query document erroneously match field in array of subdocuments using value `null`? — Neil Lunn
– Neil Lunn, Commented Feb 26, 2014 at 1:13

Bruce Lucas · Accepted Answer · 2014-02-26 21:42:18Z

0

If you know that the array never exists but is empty, as in your example data, then the following is simpler:

db.c.find({my_array: {$exists: true}})

However, if you want to filter out documents where the array exists but is empty, they your answer is good.

answered Feb 26, 2014 at 21:42

Bruce Lucas

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1 Comment

Andres Over a year ago

I think this answer is better than mine, so I'll accept it. Thanks.

Andres · Accepted Answer · 2014-02-25 23:50:14Z

0

Got it using:

db.document.find({'my_array.0': {$exists: true}})

Is there a better approach?

answered Feb 25, 2014 at 23:50

Andres

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