Let’s learn about the group addtoset in MongoDB with an example in this article. As part of our Server Management Service, Bobcares provides answers to all of your questions.

The Group addToSet in MongoDB

In MongoDB, the group will combine documents in a collection considering specific fields, whereas the $addToSet operator will gather unique values into an array. So, we can use it together to enable grouping operations while preventing duplicate values from being added to the resulting arrays.

Let’s see how it works:

1. The group aggregation step organizes documents in a collection according to specified fields. It produces groups of documents with the identical values for the specified fields.

2. The _id field in the $group stage represents the key or keys used to group the documents. It may include a single field or an expression that computes the group based on key.

3. We can then use the $addToSet operator during the $group stage to collect values into an array field. The $addToSet operator only adds values to the array if they do not already exist there.

4. If the value being added already exists in the set, it is not added again, ensuring that every value in the final array is unique.

An Example

We have a collection called sales that contains documents with the fields product and customer. The $group stage organizes documents by product field. Within each group, the $addToSet operator adds unique customer values to an array called customers. If a client appears in many documents within the same product group, they will only be added once to the customers list.

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Conclusion

We can use addToSet with $group stage to create an array that does not contain duplicate values. Here, we’ve explained it with an example from our Tech Team.