Querying internal array size in MongoDB?

You can use the $size operator for internal array size in MongoDB. The syntax is as follows:

db.internalArraySizeDemo.aggregate(    [       {          $group: {             _id:yourObjectIdValue,             anyFieldName: {$first: {$size: "$yourArrayName" }}          }       }    ] );

To understand the above syntax, let us create a collection with some documents. The query to create a collection with documents are as follows:

>db.internalArraySizeDemo.insertOne({"EmployeeName":"Mike","EmployeeTechnology":["Jav a Web Development","Python Web Development"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c6eff586fd07954a48906b2") } > db.internalArraySizeDemo.insertOne({"EmployeeName":"Sam","EmployeeTechnology":["C with Graphics","Game Development with C++ Language","MatLab"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c6effcd6fd07954a48906b3") }

Display all documents from a collection with the help of find() method. The query is as follows:

> db.internalArraySizeDemo.find().pretty();

The following is the output:

{    "_id" : ObjectId("5c6eff586fd07954a48906b2"),    "EmployeeName" : "Mike",    "EmployeeTechnology" : [       "Java Web Development",       "Python Web Development"    ] } {    "_id" : ObjectId("5c6effcd6fd07954a48906b3"),    "EmployeeName" : "Sam",    "EmployeeTechnology" : [       "C with Graphics",       "Game Development with C++ Language",       "MatLab"    ] }

Here is the query to get the internal array size with the help of $size operator:

> db.internalArraySizeDemo.aggregate( ...    [ ...       { ...          $group: { ...             _id:ObjectId("5c6eff586fd07954a48906b2"), ...             EmployeeTechnology_count: {$first: {$size: "$EmployeeTechnology" }} ...          } ...       } ...    ] ... );

The following is the output:

{ "_id" : ObjectId("5c6eff586fd07954a48906b2"), "EmployeeTechnology_count" : 2 }