Retrieve index of item in array in MongoDB

Question

similar to

-Aggregation: add option to $unwind to emit array index

-Get index of an item within mongodb query

I have this use case.

Tastiest Fruit Rankings:

{"date": "Jan 1st",
"fruit_ranking": ["Apple", "Orange", "Grape", "Kiwi", "Mango", "Pear"]},
{"date": "Jan 2nd",
"fruit_ranking": ["Orange", "Grape", "Kiwi", "Pear", "Apple"]}
.....
{"date": "Dec 31st",
"fruit_ranking":  ["Kiwi", "Apple", "Grape", "Mango", "Pear"]}

I'm trying to grab the ranking of "Pear" for each day Jan 1st - Dec 31st and right now I need to grab all of the arrays back and do indexOf in my application. Would speed up my application quite a bit if theres some way of doing this in MongoDB and just return the index of "Pear" instead of the whole Array.

I looked into Map Reduce but the documentation seem to suggest you need to have a reduce function which doesn't work.

Also looked in to Aggregation framework but this JIRA ticket seems to suggest its not implemented yet.

Lastly, I looked into Server Side Scripting but it seems too advanced for a simple use case.

Any help would be greatly appreciated!

mjkaufer · Accepted Answer · 2014-01-12 00:17:43Z

2

Haven't tested this code, but it should work.

Presuming the db name where this is stored in is tastyFruits...

tastyFruits.find({}).forEach(function(a){
console.log("Date: " + a.date);
console.log("Pear rating: " + a.fruit_ranking.indexOf("Pear"));
});

answered Jan 12, 2014 at 0:17

mjkaufer

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4 Comments

makeshifthoop Over a year ago

Interesting concept. Unfortunately that only logs the indexes in the MongoDB logs but doesn't actually return the indexes. ps. its print() and not console.log()

mjkaufer Over a year ago

If you want to return the indexes, simply push those pear ratings to an array and return the array. Not sure what language you're using, so I can't help you there.

makeshifthoop Over a year ago

Thanks! It works. Its a little bit sketchy because of injection problems but it works and its super fast.

makeshifthoop Over a year ago

hi mjkaufer, would you mind changing your answer to print instead of console.log for future clarity?

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