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collections

$push to sorted array

Aug 20 • Posted 1 year ago

By Sam Weaver, MongoDB Solutions Architect and Alberto Lerner, MongoDB Kernel Lead

MongoDB 2.4 introduced a feature that many have requested for some time - the ability to create a capped array.

Capped arrays are great for any application that needs a fixed size list. For example, If you’re designing an ecommerce application with MongoDB and want to include a listing of the last 5 products viewed, you previously had to issue a $push request for each new item viewed, and then a $pop to kick the oldest item out of the array. Whilst this method was effective, it wasn’t necessarily efficient. Let’s take an example of the old way to do this:

First we would need to create a document to represent a user which contains an array to hold the last products viewed:

db.products.insert({last_viewed:["bike","cd","game","bike","book"]})
db.products.findOne()
{
    "_id" : ObjectId("51ff97d233c4f2089347cab6"),
    "last_viewed" : [
        "bike",
        "cd",
        "game",
        "bike",
        "book"
    ]
}

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