BeforeValidate auto-generate field data for Array Field

[sksar]

Hello,
I am creating an Inventory Management System with Payload CMS.

I have a collection called purchase order that looks like this

export default {
    slug: 'purchaseOrders',
    fields: [
        {
            name: 'items',
            type: 'array',
            fields: [
                {
                    type: 'row',
                    fields: [
                        {
                            name: 'item', type: 'relationship', relationTo: 'items', hasMany: false,
                            admin: { width: '30%' },
                        },
                        {
                            name: 'buyPrice', type: 'number', required: true,
                            admin: { width: '10%' },
                        },
                        {
                            name: 'quantity', type: 'number', required: true,
                            admin: { width: '10%' },
                        },
                        {
                            name: 'amount', type: 'number',
                            admin: { width: '10%', readOnly: true },
                            hooks: {
                                beforeValidate: [(args) => {
                                    const { data } = args;
                                    console.log(data);
                                    // return ???
                                }]
                            }
                        }
                    ]
                } 
            ],
            minRows: 1,
        }
    ]
}

In the above what I want to achieve is a repeating structure of Item - Buy Price - Quantity - Amount
The amount should be calculated from the BuyPrice * Quantity.

But my problem is that in the args.data, I am getting all the data as a whole. And not the siblingFields.

So my question would be how do I scope the function or data to the row, so that I get the corresponding data.
Or how can I get the index of the function call, because in the dev console I can see that the same data is getting logged twice. (which maybe is the expected behaviour). So I can use that index to now do the scope from the array maybe.

I am stuck at this for a long time, I have searched the docs for hours, I could not figure it out in any way.

[jmikrut]

Hey @sksar — very good question.

We just published a beta (payload@0.14.27-beta.0) that includes a new siblingData argument to field hooks.

Here is the commit which includes changes to docs, but the docs changes won't hit our website until the next upcoming minor release.

Give it a shot - this should be exactly what you need! Thank you for the great request!