MongoDB $size Operator

by Online Tutorials Library July 22, 2022

MongoDB $size Operator

What is the $size operator in MongoDB?

MongoDB provides a variety of array expression operators, and the $size operator is one of those operators. The $size operator is used to find the total number of elements present in the given array, and it is also used in the aggregation pipeline stages.

Syntax of the $size operator:

Important points:

If the argument is missing, then it gives the error.
If the argument does not resolve to an array, then it gives the error.

Examples:

In the following examples, we are working with:

  Database: TutorAspire Collection: students  Document: Six documents that contain the details of the students  

>db.students.find().pretty()  {     "_id" : 1,     "name" : "Jonny",     "class" : "X",     "rollNo" : 401,     "age" : 18,     "marks" : [ 55, 60, 70, 45, 95, 68 ],     "extraMarks" : {                      "practical" : [ 21, 18, 25, 30 ],                      "attendance" : [ 5, 9 ]                    }     "gender" : "Male",     "bloodgroup" : "A+"  }  {     "_id" : 2,     "name" : "Carry",     "class" : "IX",     "rollNo" : 35,     "age" : 17,     "marks" : [ 85, 40, 90, 75, 85, 77 ],     "gender" : "Male",     "bloodgroup" : "B+"  }  {     "_id" : 3,     "name" : "Jin",     "class" : "IX",     "rollNo" : 49,     "age" : 17,     "marks" : [ 85, 70, 80, 95, 94, 81 ],     "gender" : "Female",     "bloodgroup" : "O+"  }  {     "_id" : 4,     "name" : "Thomas",     "class" : "X",     "rollNo" : 61,     "age" : 18,     "marks" : [ 91, 65, 71, 63, 98, 76 ],     "extraMarks" : {                      "practical" : [ 26, 28, 25, 29 ],                      "attendance" : [ 8, 8 ]                    }     "gender" : "Male",     "bloodgroup" : "A+"  }  {     "_id" : 5,     "name" : "Mia",     "class" : "IX",     "rollNo" : 308,     "age" : 17,     "marks" : [ 97, 98, 95, 98 ],     "gender" : "Female",     "bloodgroup" : "B+"  }  {     "_id" : 6,     "name" : "Oats",     "class" : "IX",     "rollNo" : 75,     "age" : 18,     "marks" : [ 99, 98, 98, 95, 96 ],     "gender" : "Male",     "bloodgroup" : "A+"  }

Example 1: Using $size operator

In this example, we are going to find the total size of the “marks” field using the $size operator.

  db.students.aggregate(     [       { $match : { class : “IX” }},       {         $project:            {              _id : 0,              name : 1,              class : 1,              rollNo : 1,              marks : 1,              gender : 1,              markssize : { $size: “$marks” }            }       }     ]  )  

Output:

{     "name" : "Carry",     "class" : "IX",     "rollNo" : 35,     "marks" : [ 85, 40, 90, 75, 85, 77 ],     "gender" : "Male",     "markssize" : 6  }  {     "name" : "Jin",     "class" : "IX",     "rollNo" : 49,     "marks" : [ 85, 70, 80, 95, 94, 81 ],     "gender" : "Female",     "markssize" : 6  }  {     "name" : "Mia",     "class" : "IX",     "rollNo" : 308,     "marks" : [ 97, 98, 95, 98 ],     "gender" : "Female",     "markssize" : 4  }  {     "name" : "Oats",     "class" : "IX",     "rollNo" : 75,     "marks" : [ 99, 98, 98, 95, 96 ],     "gender" : "Male",     "markssize" : 5  }

Example 2: Using $size operator in the embedded document

In this example, we are going to find the total size of the extraMarks.practical field using the $size operator.

  db.students.aggregate(     [       { $match : { class : “X” }},       {         $project:            {              _id : 0,              name : 1,              class : 1,              rollNo : 1,              marks : 1,              extraMarks : 1              gender : 1,              result : { $size: “$extraMarks.practical” }            }       }     ]  )  

Output:

{     "name" : "Jonny",     "class" : "X",     "rollNo" : 401,     "marks" : [ 55, 60, 70, 45, 95, 68 ],     "extraMarks" : {                      "practical" : [ 21, 18, 25, 30 ],                      "attendance" : [ 5, 9 ]                    }     "gender" : "Male",     "result" : 4  }  {     "name" : "Thomas",     "class" : "X",     "rollNo" : 61,     "marks" : [ 91, 65, 71, 63, 98, 76 ],     "extraMarks" : {                      "practical" : [ 26, 28, 25, 29 ],                      "attendance" : [ 8, 8 ]                    }     "gender" : "Male",     "result" : 4  }

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MongoDB $size Operator

MongoDB $size Operator

What is the $size operator in MongoDB?

Syntax of the $size operator:

Examples:

JavaScript TypedArray subarray() Method

PHP str_replace() Function

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