In MongoDB, the $exists operator is used to check whether a field exists in a document or not. The $exists operator takes a boolean value (either true or false) as its argument.
To use the $exists operator, you can use it in a query with the dot notation. For example, if you want to find all documents that have a field called field1, you can use the following query:
db.collection.find({field1: {$exists: true}})
This will return all documents in the collection that have the field1 field.
You can also use the $exists operator to apply conditions to a field. For example, suppose you have a collection of products with a field called quantity. You can use the $exists operator to find all products that have a quantity greater than zero as follows:
db.products.find({quantity: {$exists: true, $gt: 0}})
This will return all products in the collection that have a quantity field and the value of the quantity is greater than zero.
It is important to note that the $exists operator does not check the value of the field. It only checks whether the field exists or not. Therefore, if you want to find documents where a field exists and has a specific value, you should use a query that combines the $exists operator with another operator, such as $eq, $ne, $gt, $gte, $lt, or $lte.
