MongoDB, array of arrays index

Question

Can I have an index on subarrays?

Sample document:

{ 
    'who': [['en', 'Thomas'], ['es', 'Alfonzo'], ['de', 'Helmut']],
    'otherField': 123
}

Query:

{'who': 
    { '$elemMatch': { '1': 'Helmut'} } 
}

I need an index for this type of queries. Thanks.

Have you considered just storing the data as 'who': [ { lang: 'en', name: 'Thomas' }, ... ]? — WiredPrairie
– WiredPrairie, Commented May 3, 2013 at 17:37
Yes, but I prefer using arrays if possible. (edit: I mistakely deleted this comment from yesterday) — sthr
– sthr, Commented May 4, 2013 at 7:17

Paul · Accepted Answer · 2013-05-03 22:22:57Z

1

Using arrays like this isn't the best structure, because you're forcing several rather conditions on your data.

Something like this

...
"who": [{
  "language": "en", "text": "Thomas'
}, ... ]
...

EDIT: (Removed previous suggestion)

Then, as Jim Dagg pointed out, you could create an index on who.text.

edited May 3, 2013 at 22:22

answered May 3, 2013 at 17:46

Paul

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3 Comments

Jim Dagg Over a year ago

If you use subdocuments inside an array like in your first code block, you can use a multikey index against who.text.

sthr Over a year ago

Thanks. I know I can use index if I use subdocuments instead of arrays, but I prefer using arrays if possible. If I understand the situation well, it is not possilbe to index array of arrays so I must use subdocuments.

Paul Over a year ago

Apologies then, but you're never really sure how much the OP knows, especially for newish technology like MongoDB. :) If it is any consolation, this is a better data structure than using nested arrays.

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