Tuples in Mongo document with same key?

[Russell Bateman]

Is there no way in Mongo to get a document that looks like the one I'm trying to insert here?

> db.subs.insert( { "x":9, "tuple":"value", "tuple":"value", "tuple":"different value" } );

> db.subs.findOne();
{
    "_id" : ObjectId("50356db633f95e308785e7d4"),
    "x" : 9,
    "tuple" : "different value"
}

> db.subs.insert( { "x":9, "data": { "tuple":"value", "tuple":"value", "tuple":"different value" } } );

> db.subs.findOne();
{
    "_id" : ObjectId("50356db633f95e308785e7d5"),
    "x" : 9,
    "data" : {
        "tuple" : "different value"
    }
}

Note that the first two tuples were ignored/dropped/overwritten, and not just because they had the same value. I'm not totally surprised by this, but I wondered. Certainly it's the case in the Java driver, in BasicDBObject, that stuff is done in a Map which doesn't allow multiple identical keys so it's doubtful I could get anything back anyway.

Would someone like to growl at me or discuss this? If it worked, I could make use of it and in fact had been blithely writing code as if it worked until a little while later noticing that it did not.

Many thanks.

[Kristina Chodorow]

BSON doesn't specifically disallow it, but most languages don't support it.  C++ and C do, but languages that implement documents as hashes can't.  Even if you saved a doc with duplicate keys in C/C++, you wouldn't be able to see them in the shell.  And querying for it would be kind of wacky.  So, generally don't do that.

Is there a reason you can't do tuple:["value", "value", "different value"]?

[Russell Bateman]

Thank you for responding. I think I just wanted confirmation--to make certain that I wasn't missing out on something that could be (appropriately) done. I have indeed decided to use an alternate representation, possibly the one you suggest or maybe just a space-delimited string (since the values I really want are identifiers with no spaces or punctuation rather than what my example showed).

Thanks, Kristina.

Russ

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