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 }