Before change event

[bkniffler]

Is your feature request related to a problem? Please describe.
The change will not allow me to modify a row. Say I want to create a plugin to update updatedOn field each time a row is updated, how can I manage this?

Describe the solution you'd like
Maybe a "beforeChange" hook? Or make the change hook allow to return Promise or call a callback with an updated item. Or just call the change hook before actual writing to storage so that mutation on event.result will be persisted.

[only-cliches]

This is thoroughly implemented with filters, documented in the plugin docs here.

A quick example to implement what you're asking for:

nSQL().connect({
    tables: [...],
    plugins: [
        {
            name: "My Plugin",
            version: 1.0,
            dependencies: {},
            filters: [
                {
                    name: "adapterWrite",
                    priority: 1000,
                    call: (inputArgs: {res: {table: string, pk: any, row: any, complete: () => void, error: () => void}, query: InanoSQLQuery}, complete, cancel) => {
                        // passthrough
                        complete(inputArgs)
                    }
                }
            ]
        }
    ]
})

This filter is called before rows are written into the database from upsert queries, works for new rows and rows being updated.

Hope that makes sense!