There are a number of quarky little MongoDB commands and queries hidden in the docs, two of them are $size and $type.
Does it really matter? $size that is …
The $size operator matches any array with the specified number of elements.
The basic use would be something like …
> db.ideas.find( { votes : { $size: 2 } } );
That would get you all the documents in the ideas collection that have exactly 2 items in the votes array (if say, you kept an array of votes.)
This however is of somewhat dubous use as:
You cannot use $size to find a range of sizes.
Meaning you can’t query for ideas that have 2 or more votes, or between 2 and 25 votes.
Are you her $type?
Another interesting query modifier is $type …
The $type operator matches values based on their BSON type.
This might be useful to seek out documents that have a property that is an int and not a string; the types correspond numeric IDs (see the list below.)
To get documents with a property which has a value that is of the type of int the query might look something like this …
> db.mycollection.find( { foo : { $type : 16 } } );
Again, the practical usefulness of this might be rather thin, but who knows … it might come in handy someday!
MongoDB BSON Types
|
|
|---|---|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
