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Mongo aggregation grouping by categories then grouping by subcategories
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| consider the collection shown below | |
| [ | |
| { | |
| _id: 1, | |
| category: "A", | |
| subCategory: "a1", | |
| }, | |
| { | |
| _id: 2, | |
| category: "A", | |
| subCategory: "a1", | |
| }, | |
| { | |
| _id: 3, | |
| category: "A", | |
| subCategory: "a2", | |
| }, | |
| { | |
| _id: 4, | |
| category: "C", | |
| subCategory: "c2", | |
| }, | |
| { | |
| _id: 5, | |
| category: "B", | |
| subCategory: "b1", | |
| }, | |
| { | |
| _id: 6, | |
| category: "B", | |
| subCategory: "b1", | |
| } | |
| ] | |
| the following aggregation will group the documents per category and sub category. this is very useful for e-commerce faceted search | |
| db.collection.aggregate([ | |
| { | |
| $group: { | |
| _id: { | |
| category: "$category", | |
| subCategory: "$subCategory" | |
| }, | |
| count: { | |
| $sum: 1 | |
| } | |
| } | |
| }, | |
| { | |
| $group: { | |
| _id: "$_id.category", | |
| v: { | |
| $push: { | |
| subCategory: "$_id.subCategory", | |
| sum: "$count" | |
| } | |
| }, | |
| s: { | |
| $sum: "$count" | |
| } | |
| } | |
| }, | |
| ]) | |
| the result obtained form the above aggregation pipeline is as follows | |
| [ | |
| { | |
| "_id": "B", | |
| "count": 2, | |
| "v": [ | |
| { | |
| "subCategory": "b1", | |
| "sum": 2 | |
| } | |
| ] | |
| }, | |
| { | |
| "_id": "A", | |
| "count": 3, | |
| "v": [ | |
| { | |
| "subCategory": "a1", | |
| "sum": 2 | |
| }, | |
| { | |
| "subCategory": "a2", | |
| "sum": 1 | |
| } | |
| ] | |
| }, | |
| { | |
| "_id": "C", | |
| "count": 1, | |
| "v": [ | |
| { | |
| "subCategory": "c2", | |
| "sum": 1 | |
| } | |
| ] | |
| } | |
| ] | |
| see the mongo playground at https://mongoplayground.net/p/WfEC2xAmriJ |
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