How to create "trigger" in MongoDB

Question

I would like of create a trigger where, to each subdocument inserted would increment in other collection a field, for generate a count of subdocuments that collection.

I tried create a search using MapReduce, but for Milions of the Registries is very slow.

Note: I use C#, but if you like show how to do in Bson, no problem.

Extructure my collection

public class Header
{
    public Header()
    {
        Operation= new List<Operation>();
    }

    public ObjectId Id { get; set; }
    public Int64 Code1 {get; set;}
    public Int64 Code2 {get; set;}
    public string Name { get; set; }
    public List<Operation> Operations { get; set; }
}

public class Operation
{
    public Operation()
    {
        Itens = new List<Item>();
    }

    public string Value { get; set; }
    public List<Item> Item { get; set; }
}

public class Item
{
    public string Value { get; set; }
}

Solution 1

MongoDB has no triggers. You will have to implement this in your application by inserting the document and when the insert was successful, you use the $add operator to increment the field in the other document.

Update: If you happen to rent a MongoDB Atlas instance from a service provider, then you can use triggers. But if you want to run MongoDB on your own servers, then this feature is not available.

Solution 2

MongoDB does in 2020 since July 2019, have triggers. https://docs.mongodb.com/stitch/triggers/database-triggers/

Solution 3

You can use change streams, specifically the collection.watch method available in drivers.

Database triggers from MongoB Atlas use these under the hood.

Comments

[Renatto Machado]

I know that MongoDB not has trigger. But, I can not use function for this?

[Renatto Machado]

No see how $add oprator can help me. I Ready documentation, but no see how resolve my question.

[Renatto Machado]

Not was used $add operator, but use the ideia for design solution where i created a collection count for each document of the my collection.

[Heiko Scholze]

Database Triggers are only available for MongoDB Atlas clusters that are running MongoDB version 3.6 or newer!