GQL: is myList.contains(myField) any faster than 30 separate myField == myList(i) queries?

I've got a list with 100 Longs in it, and an Entity kind with a Long field. I want to find all the entities whose field value is in the list.

I was thinking, "Great! I'll just write where :p1.c开发者_如何学编程ontains(field)," but AppEngine will only split this out on less than 31 elements (new Baskin Robbins' slogan?). So, now I'm thinking I'll have to split the list of 100 into multiple lists of 30.

But at this point, my hopes of a one-liner shot, I realized I could do something like

for (Long number : list)
    GQL("select * from Kind where field = " + number)

essentially splitting into all the subqueries myself. My question is... is this equivalent to letting appengine split my list of 30 into 30 separate queries? Or is there some back-end magic they do to fetch all 30 sub-queries simultaneously?

Sub-queries are functionally identical to regular queries. Currently, sub-queries are run serially, so doing it yourself isn't going to be any slower than letting the SDK do it for you. In future, though, it's likely that sub-queries will be executed in parallel, making them much more efficient than doing it yourself. It's also possible functionality like 'IN' could be pushed to the backend, avoiding the issue in the app server altogether.

You should be aware, though, that anything that requires you to execute 100 queries is going to be very, very slow. If you can, you should find a way to work around this without doing piles of queries and merging the results.

That function likely utilizes the IN (arg1,arg2,...) operator.

The problem being:

A single query containing != or IN operators is limited to 30 sub-queries.

Each item in the list counts as a sub query so you can only fetch 30 items at a time with that query style.

Using SELECT * FROM YourKind WHERE value IN list_property will cause multiple sub-queries to be run. It is these sub-queries that are limited to 30.

Using SELECT * FROM YourKind WHERE list_property = value will use the index that is built for your list_property so should work with as many entries as your list-property can contain†.

† I think this would be limited to the 5000 max items for an index