MongoDB query to find the list in nested array

Question

I have a collection with documents are like this:

{
    "date" : 20200817,
    "items" : [ 
        {
            "name" : "item1", "values" : ["val1", "val2", "val3", "val4"]
        }, 
        {
            "name" : "item2", "values" : ["val1", "val4"]
        }, 
        {
            "name" : "item3", "values" : ["val1", "val3"]
        }
    ]
}

I want to get list of name of items that val3 is exist in values like this

['item1', 'item3']

I have this query :

db.test.find({
    'dateM': 20200817,
    'items': {
        '$elemMatch':{
            'values':{
                '$elemMatch':{
                    $in:['val3']
                }
            }
         }
     }
}, {'lists.name': 1})

but i get list of name of all items.

Where is my query wrong?

What can I do?

Thanks

varman · Accepted Answer · 2020-08-31 11:40:53Z

1

You need to use aggregation there. This is one way you can achieve

[
  {
    $project: {
      output: {
        $map: {
          input: {
            $filter: {
              input: "$items",
              cond: {
                $in: [
                  "val3",
                  "$$this.values"
                ]
              }
            }
          },
          in: "$$this.name"
        }
      }
    }
  }
]

Working Mongo playground

edited Aug 31, 2020 at 11:40

answered Aug 31, 2020 at 11:19

varman

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Comments

Joe · Accepted Answer · 2020-08-31 11:01:11Z

0

The query you have should return only documents that contain at least one item with val3.

If returning only the first matching element is sufficient, you use the projection form of $elemMatch, otherwise, you will need to either use aggregation or filter the array on the client side.

answered Aug 31, 2020 at 11:01

Joe

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