Mongodb nested array group with key value array count

Question

I have mongodb structure like below:

{
"_id":"123456789",
"name":"item name 1",
"variants":[
    {
    "size":"150 ml",
    "filters":[

    {"name":"filter 1",
    "value":"value 1"},
    {"name":"filter 2",
     "value":"value 2"}
  ]
   } 
]
},

{
"_id":"987654321",
"name":"item name 1",
"variants":[
    {
    "size":"200 ml",
    "filters":[

    {"name":"filter 1",
    "value":"value 2"},
    {"name":"filter 2",
     "value":"value 1"}
  ]
   } 
]
}

Now i want count of filter with group by name and value. i.e.

[{filter 1:[{value:value 1, count:10}, {value: value 2, count:5}]},
{filter 2:[{value:value 1, count:5}, {value: value 2, count:2}]}

or

  [{name:filter 1, value:value 1, count:10}, {name:filter 1, value:value 2, 
count:5}]

how to achieve this using mongodb aggregrate and group query?

See this Aggregation $group example, which has group by multiple fields (like your problem). — prasad_
– prasad_, Commented Oct 30, 2019 at 14:23

Haruo · Accepted Answer · 2019-10-30 14:45:38Z

3

You can try this Way:

db.collection.aggregate([
    { $unwind: "$variants" },
    { $unwind: "$variants.filters" },
    { $group:
        {
            _id: "$variants.filters",
            count:{$sum:1}
        }
    },
    { $addFields: {"name" : "$_id.name", "value" : "$_id.value"}},
    { $project: {_id: 0} }
]);

A working example at https://mongoplayground.net/p/an2xVfDusJn.

edited Oct 30, 2019 at 14:45

answered Oct 30, 2019 at 14:27

Haruo

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4 Comments

prasad_ Over a year ago

The last stage { $project: {_id: 0} } can be removed and the _id: 0 can be projected in the addFields stage itself..

Mihir Shah Over a year ago

@prasad_, it is 0.0 in this case if i put _id:0 at addfields level.

prasad_ Over a year ago

@MihirShah You are right. Replace $addFields and $project with this: { $project: { name : "$_id.name", value : "$_id.value", count: 1, _id: 0 } }.

prasad_ Over a year ago

@MihirShah Having extra stages can be sometimes a performance problem, especially if number of documents are large. So, its a just a good practice to avoid those always.

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