How to add leading zeros in mongodb?

@addison 

To add leading zeros to a field in a MongoDB collection, you can use the $lpad operator in the $project stage of an aggregation pipeline. The $lpad operator allows you to pad a string with a specified number of zeros, or any other character, on the left side until it reaches a desired length.

Here's an example of how you can use the $lpad operator to add leading zeros to a field called number:

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db.collection.aggregate([
   {
      $project: {
         paddedNumber: { $lpad: [ "$number", 10, "0" ] }
      }
   }
])

This will add leading zeros to the number field until it reaches a length of 10 characters. If the original value of number is less than 10 characters long, it will be padded with zeros on the left. If it is already 10 characters or longer, it will not be modified.

You can also use the $lpad operator in a $update operation to update the value of the field directly in the collection. For example:

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db.collection.update(
   {},
   { $set: { paddedNumber: { $lpad: [ "$number", 10, "0" ] } } },
   { multi: true }
)

This will update all documents in the collection, setting the value of the paddedNumber field to the value of the number field padded with zeros on the left until it reaches a length of 10 characters.