How to mimic SQL subselect during a mutation?

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1

I’m pretty sure you can’t do this in Graphql, but maybe DQL. This is a pretty huge deal, and I can’t find anything in the docs or on here that does this effectively.

The inability to effectively and efficiently do migrations is a big sticking point for me right now. The inability to do much of anything across relationships is a paint point (IE- filter on a property of a relationship in Graphql).

Example:
Given an item that has a price.
Let’s say I stored the price separately for a bit on a priceHistory.
But now I’ve learned I don’t need or want it and want to move the most recent (last) price from the history and place it directly on the item.

PriceHistory = {on: DateTime, value: Int}
Item = {id: ID!, priceHistory: [PriceHistory!]}

In SQL we’d simply do this:

update Item set price = (select value, on from priceHistory where priceHistory.itemId = Item.id order by on desc limit 1;

I wrote a mutationLambda to try and do this for me, but I can’t process more than about 200 records per call. It’s just too slow, which worries me about dgraphs long term performance…

2

This is basically the concept of upsert with DQL.

Build any kind of DQL query and set any field/value to a variable, then use that variable in a set or delete statement.