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    <p>First, note that your sort example is malformed: the aggregate method takes an array as input, where each element in the array specifies a stage in an aggregation pipeline. Also, note that the <a href="http://docs.mongodb.org/manual/reference/operator/elemMatch/">$elemMatch</a> operator cannot be used as part of a $sort stage.</p> <p>One way to achieve what you're trying to do with your sort example is use the aggregation framework's <a href="http://docs.mongodb.org/manual/reference/aggregation/unwind/">$unwind</a> pipeline operator. Unwinding an array will peel the array elements off one-by-one into separate documents. For example, the following query</p> <pre><code>db.my_collection.aggregate([ {$unwind: "$answers"} ]); </code></pre> <p>returns something like the following:</p> <pre><code>[ { "_id" : ObjectId("5237157f3fac8e36fdb0b96e"), "user" : "bruno", "answers" : { "id" : 0, "value" : 3.5 } }, { "_id" : ObjectId("5237157f3fac8e36fdb0b96e"), "user" : "bruno", "answers" : { "id" : 1, "value" : "hello" } }, { "_id" : ObjectId("523715813fac8e36fdb0b96f"), "user" : "bruno2", "answers" : { "id" : 0, "value" : 0.5 } }, { "_id" : ObjectId("523715813fac8e36fdb0b96f"), "user" : "bruno2", "answers" : { "id" : 1, "value" : "world" } } ] </code></pre> <p>Adding a $match phase will allow you to grab only the documents where answers.id is zero. Finally, a $sort phase allows you to sort by answers.value. All together the aggregation query is:</p> <pre><code>db.my_collection.aggregate([ {$unwind: "$answers"}, {$match: {"answers.id": 0}}, {$sort: {"answers.value": -1}} ]); </code></pre> <p>And the output:</p> <pre><code>[ { "_id" : ObjectId("5237157f3fac8e36fdb0b96e"), "user" : "bruno", "answers" : { "id" : 0, "value" : 3.5 } }, { "_id" : ObjectId("523715813fac8e36fdb0b96f"), "user" : "bruno2", "answers" : { "id" : 0, "value" : 0.5 } } ] </code></pre> <p>Based on what your asking, it doesn't sound like you'll always need $unwind or even the aggregation framework. If instead you wanted to find the document with answers.id equal to 0 and answers.value equal to 3.5, and then change answers.value to 4 you could use find with $elemMatch followed by db.collection.save():</p> <pre><code>doc = db.my_collection.findOne({"answers": {$elemMatch: {"id": 0, "value": 3.5}}}); for (i=0; i&lt;doc.answers.length; i++) { if (doc.answers[i].id === 0) { doc.answers[i].value = 4; db.my_collection.save(doc); break; } } </code></pre>
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    1. COI've been researching and found that the model of my JSON was complicated then proposed for applications developers a simpler way that I see it facilitated the development. Thank you for your solution, I learn a lot and understand your purpose.
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      1. USBruno Gabriel dos Santos
 

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