check array length mongodb code example

Example 1: mongo count elements in array

> db.mycollection.insert({'foo':[1,2,3,4]})
> db.mycollection.insert({'foo':[5,6,7]})

> db.mycollection.aggregate([{$project: { count: { $size:"$foo" }}}])
{ "_id" : ObjectId("5314b5c360477752b449eedf"), "count" : 4 }
{ "_id" : ObjectId("5314b5c860477752b449eee0"), "count" : 3 }

Example 2: query document array size greater than 1

// Find all docs that have at least two name array elements.
db.accommodations.find({'name.1': {$exists: true}})

Example 3: mongo count elements in array

{ $size: <expression> }

Example 4: mongodb count array size

db.inventory.aggregate([
   {
      $project: {
         item: 1,
         numberOfColors: { $cond: { if: { $isArray: "$colors" }, then: { $size: "$colors" }, else: "NA"} }
      }
   }
] )