Hook into bulkWrite

[jaschaio]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the feature has not already been requested

🚀 Feature Proposal

Mongoose already supports middlewares for the majority of operations. But by reviewing the documentation and code I couldn't find a way to hook into bulkWrite.

Which I found surprising, as castBulkWrite is called on each bulkWrite operation giving at least a perfect entry point for
pre modifying bulkWrite operations before they are executed:

mongoose/lib/model.js

Line 3424 in ebf7d07

const validations = ops.map(op => castBulkWrite(this, op, options));

This allows mongoose internally for example to add the discriminator:

https://github.com/Automattic/mongoose/blob/master/lib/helpers/model/castBulkWrite.js#L70

Or updatedAt and createdAt timestamps:

https://github.com/Automattic/mongoose/blob/master/lib/helpers/model/castBulkWrite.js#L75

Motivation

I am already using mongoose discriminators to clearly seperate tenants within a single database.

Mongoose only allows setting a single discriminatorKey per model, so if I would like to "discriminate" additionally on another key I can't use discriminators for it.

Now I want to shard data based on geolocation for which each query needs to include both the discriminatorKey and the location. This is fairly easy to accomplish via hooks:

// ... higher order method that calls each model with the location

// Modify mongoose queries to include location
Model.schema.pre( /find|update/, function () {

    this.setQuery( { ...this.getQuery(), location } );

} );

// Add a $match location stage to the beginning of each aggregation pipeline
Model.schema.pre( 'aggregate', function() {

    this.pipeline().unshift( { $match: { location } } );

} );

But this doesn't touch bulkWrite operations. Here I would have to remember to include the location within each filter key. I would prefer if I could just hook into the castBulkWrite method instead similar to how mongoose is doing it internally with discriminators.