FWD » Core Development » Database

I assume we already do this, but just in case, does CAN-FIND avoid hydration?

It does, if we implement it as a sub-select (i.e., when it is a nested CAN-FIND in another query's WHERE clause).

It does not avoid hydration as a standalone FindQuery. Not hydrating a DMO is a relatively recent topic of discussion. Currently (until we implement #6720), every query (without a FIELDS/EXCEPT clause) which resolves to a record fully hydrates. Once #6720 is implemented, we will get this for free, but I think we can do even better by altering the conversion of a standalone CAN-FIND to either be:

• (for CAN-FIND(...)): a projection query returning only the record's primary key;
• (for CAN-FIND(FIRST/LAST ...)): an exists query.

This is similar to the approach we use for the sub-selects, when CAN-FIND is nested. There is no need to bring back the DMO's data at all in these cases.

I found Ovidiu's comment in #5453-2 relevant for this task.

I've tested both temporary and persistent tables with CAN-FIND and nested CAN-FIND. CAN-FIND no longer hydrates with trunk/rev.14552. My examples consisted of using CAN-FIND with FIRST, LAST or no keyword.