MongoDB Change The Type of a field – Guidelines

Today in this article, we will learn MongoDB Change The Type of a field. There are multiple approaches to achieving the data type change as explained below,

• Change data type using Mongo Compass UI or any other UI –Manual way
• Change data type in Mongo Using Aggregation Type Expression Operators – An automated way
  • Using Aggregation Operators like $toInt , $toString
  • Using Aggregation Operators like $convert

We will cover various 3-4 approaches to perform the datatype change feature.

Overall, We will cover the below aspects,

The below approach discussed is very useful when you don’t want to delete or drop the mongo fields but rather want to change the type of a field.

I have below Mongo Collection where my fields are defined as below.

I have a field name called “EmpID” which is of type “string“. I want to change this field to “int” using MongoShell.

Change data type using Mongo Compass UI or any other UI –Manual way

One can easily change the data type of a field in the Mongo DB document

In Mongo Atlas click on Edit Document. Here you will get an option to choose the data type,

As shown above, the manual approach can be used as needed.

Change data type in Mongo Using Aggregation Type Expression Operators – An automated way

Please open the command prompt or Mongo shell and log in to your database using a connection string.

We will first login to MongoDB and then switch to using the required database and the collection

Command Pattern

db.<collection-name>.update( {}, [ {$set:{ "<field-name>" : {$<field type>: "$<field-name>"}}} ]

Example – Convert string to numerical values in MongoDB

Example

db.employee.update({}, [ {$set:{ "EmpID" : {$toInt: "$EmpID"}}} ], {multi:true})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

Example – Convert a numeric value to a string in MongoDB

Command:

db.employee.update({}, [ {$set:{ "EmpID" : {$toString: "$EmpID"}}} ], {multi:true})

Example

db.employee.update({}, [ {$set:{ "EmpID" : {$toString: "$EmpID"}}} ], {multi:true})
WriteResult({ "nMatched" : 5, "nUpserted" : 0, "nModified" : 5})

Example – Convert a NumberLong to a String

Command:

db.employee.update({}, [ {$set:{ "Ssn" : {$toString: "$Ssn"}}} ], {multi:true})

In the above example, Ssn is a long number data type field that we are converting to string type.

Using Aggregation Operators like $convert

Using this option, one can easily create an aggregation pipeline using $Convert operation which lets you convert field type easily.

Example:

db.employee.aggregate(
  [
    {
      $project:
        { 
          result: 
          {
            $convert: { 
              input: "$EmpID", 
              to: "string",
              onError: "An error occurred for the conversion",
              onNull: "Input was null or empty" 
            }
          }
        }
    }
  ]
).pretty()

With pretty print, you can get the expression results on the screen as shown above.

Do you have any comments or ideas or any better suggestions to share?

Please sound off your comments below.

Happy Coding !!

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