How do i filter an array in mongodb?

The following example queries for documents where the dim_cm array contains elements that in some combination satisfy the query conditions; e.g., one element can satisfy the greater than 15 condition and another element can satisfy the less than 20 condition, or a single element can satisfy both:

Use $elemMatch operator to specify multiple criteria on the elements of an array such that at least one array element satisfies all the specified criteria.

The following example queries for documents where the dim_cm array contains at least one element that is both greater than ($gt) 22 and less than ($lt) 30:

Using dot notation, you can specify query conditions for an element at a particular index or position of the array. The array uses zero-based indexing.

Note

When querying using dot notation, the field and nested field must be inside quotation marks.

The following example queries for all documents where the second element in the array dim_cm is greater than 25:

Use the $size operator to query for arrays by number of elements. For example, the following selects documents where the array tags has 3 elements.

This example uses the sales collection from the previous example.

The example uses the limit field to specifiy the number of matching elements returned in each items array.

db.sales.aggregate( [
   {
      $project: {
         items: {
            $filter: {
               input: "$items",
               cond: { $gte: [ "$$item.price", 100 ] },
               as: "item",
               limit: 1
            }
         }
      }
   }
] )

The operation produces the following results:

{
   "_id" : 0,
   "items" : [
      { "item_id" : 2, "quantity" : 1, "price" : 240 }
   ]
}
{
   "_id" : 1,
   "items" : [
      { "item_id" : 23, "quantity" : 3, "price" : 110 }
   ]
}
{ "_id" : 2, "items" : [ ] }

This example uses the sales collection from the previous example.

The following example uses a numeric expression for the limit field to specifiy the number of matching elements returned in each items array.

db.sales.aggregate( [
   {
      $project: {
         items: {
            $filter: {
               input: "$items",
               cond: { $lte: [ "$$item.price", 150] },
               as: "item",
               limit: 2.000
            }
         }
      }
   }
] )

The operation produces the following results:

{
   "_id": 0,
   "items": [
      { "item_id": 43, "quantity": 2, "price": 10 }
   ]
},
{
   "_id": 1,
   "items": [
      { "item_id": 23, "quantity": 3, "price": 110 },
      { "item_id": 103, "quantity": 4, "price": 5 }
   ]
},
{
   "_id": 2,
   "items": [
      { "item_id": 4, "quantity": 1, "price": 23 }
   ]
}

This example uses the sales collection from the previous example.

The example uses a limit field value that is larger than the possible number of matching elements that can be returned.

db.sales.aggregate( [
   {
      $project: {
         items: {
            $filter: {
               input: "$items",
               cond: { $gte: [ "$$item.price", 100] },
               as: "item",
               limit: 5
            }
         }
      }
   }
] )

The operation produces the following results:

[
   {
      "_id": 0,
      "items": [
      { "item_id": 2, "quantity": 1, "price": 240 }
      ]
   },
   {
      "_id": 1,
      "items": [
         { "item_id": 23, "quantity": 3, "price": 110 },
         { "item_id": 38, "quantity": 1, "price": 300 }
      ]
   },
   {
      "_id": 2,
      "items": []
   }
]