MongoDB select distinct and count -


i have product collection looks that:

products = [   {       "ref": "1",       "facets": [         {            "type":"category",           "val":"kitchen"          },         {            "type":"category",           "val":"bedroom"          },         {            "type":"material",           "val":"wood"          }                    ]   },   {       "ref": "2",       "facets": [         {            "type":"category",           "val":"kitchen"          },         {            "type":"category",           "val":"livingroom"          },         {            "type":"material",           "val":"plastic"          }                   ]   } ]

i select , count distinct categories , number of products have category (note product can have more 1 category). that:

[   {     "category": "kitchen",     "numberofproducts": 2   },   {     "category": "bedroom",     "numberofproducts": 1   },   {     "category": "livingroom",     "numberofproducts": 1   } ]

and better if same result each different facet type, that:

[   {     "facettype": "category",     "distinctvalues":           [             {               "val": "kitchen",               "numberofproducts": 2             },             {               "val": "livingroom",               "numberofproducts": 1             },             {               "val": "bedroom",               "numberofproducts": 1             }           ]   },   {     "facettype": "material",     "distinctvalues":           [             {               "val": "wood",               "numberofproducts": 1             },             {               "val": "plastic",               "numberofproducts": 1             }           ]   } ]

i doing tests distinct, aggregate , mapreduce. can't achieve results needed. can tell me way?

update:

with aggregate, give me different facet categories product have, not values nor count of different values:

db.products.aggregate([     {$match:{'content.facets.type':'category'}},      {$group:{ _id: '$content.facets.type'} }   ]).pretty();

the following aggregation pipeline give desired result. in first pipeline step, need $unwind operation on facets array it's deconstructed output document each element. after $unwind stage first of $group operations groups documents previous stream category , type , calculates number of products in each group using $sum. next $group operation in next pipeline stage creates array holds aggregated values using $addtoset operator. final pipeline stage $project operation transforms document in stream modifying existing fields:

var pipeline = [     { "$unwind": "$facets" },     {         "$group": {             "_id": {                 "facettype": "$facets.type",                 "value": "$facets.val"             },             "count": { "$sum": 1 }         }     },     {         "$group": {             "_id": "$_id.facettype",             "distinctvalues": {                 "$addtoset": {                     "val": "$_id.value",                     "numberofproducts": "$count"                 }             }         }     },     {         "$project": {             "_id": 0,             "facettype": "$_id",             "distinctvalues": 1         }     } ];  db.product.aggregate(pipeline);

output

/* 0 */ {     "result" : [          {             "distinctvalues" : [                  {                     "val" : "kitchen",                     "numberofproducts" : 2                 },                  {                     "val" : "bedroom",                     "numberofproducts" : 1                 },                  {                     "val" : "livingroom",                     "numberofproducts" : 1                 }             ],             "facettype" : "category"         },          {             "distinctvalues" : [                  {                     "val" : "wood",                     "numberofproducts" : 1                 },                  {                     "val" : "plastic",                     "numberofproducts" : 1                 }             ],             "facettype" : "material"         }     ],     "ok" : 1 }

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