MongoDB: Cumulative values of all fields of a specific subdocument
I am trying to use MongoDB aggregate structure to create documents from a collection, which has the following structure:
{
"_id" : ObjectId("5510eb56f877bbef153d236d"),
"attributes" : {
"brand" : "Mercedes",
"price" : 289,
"family" : "GARDEN"
},
"name" : "Bigger Fix Soft Crisps"
}
{
"_id" : ObjectId("5510eb56f877bbef153d236e"),
"attributes" : {
"brand" : "Adelholzener",
"price" : 683,
"family" : "COMPUTER"
},
"name" : "Soft Stockhome Chips"
}
{
"_id" : ObjectId("5510eb56f877bbef153d236f"),
"attributes" : {
"brand" : "Pepsi",
"price" : 789,
"family" : "CAR"
},
"name" : "Light Yearsailfresh Meat"
}
I want to get an aggregation of all fields from a subdirectory attributes
with their possible values. Since the fields in the sub-document are not known, I cannot just use the fields given in this example and therefore must be dynamic. The result should look something like this:
{
"_id" : "brand",
"values" : [
"Mercedes", "Adelholzener", "Pepsi"
]
},
{
"_id" : "price",
"values" : [
289, 683, 789
]
},
{
"_id" : "family",
"values" : [
"GARDEN", "COMPUTER", "CAR"
]
}
I haven't found a solution for this specific problem yet. I've tried with $project
and $unwind
(which obviously only works for arrays).
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Tried to figure out how to do this, aggregate, but I'm not sure if this is possible as you cannot get the keys in an object in any convenient way.
Here is MapReduce doing the following:
db.runCommand({
"mapreduce" : "test_collection", // Change collection here
"map" : function() {
for (var key in this.attributes) {
// Emit objects w array as we cannot reduce arrays directly
emit(key, {x: [this.attributes[key]]});
}
},
"reduce" : function(key, values) {
var res = [];
values.forEach(function (d) {
Array.prototype.push.apply(res, d.x);
});
return {x: res};
},
"finalize": function (key, reducedVal) {
return reducedVal.x;
},
"out": { inline: 1 }
});
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