WFCORE-287 will introduce a new 'query' operation. But in a mixed domain, slaves running legacy versions will not understand that operation. So the console, when managing such a domain will either need to analyze the management API version of each host and not target 'query' ops to legacy hosts, or we need to figure out a way to emulate support on the DC.

One thought I had was to use a transformer. My understanding of how query works is it's essentially a read-resource and then some post-processing is applied to filter the result. So my thought is an operation transformer can convert the query op to a read-resource op, which the slave will understand, and then a result transformer on the DC does the filtering work.

There may of course be gotchas there.

One issue I see is I think this query op is going to be a global op. I don't believe we currently have hooks for registering transformers for global ops. That is, there's nothing like the 'inherited' handling we use for registering the handler for the global op and then discovering it when resolving the operation name against child resource registrations.

Another issue to remember is 'query' op will support wildcard addresses, so the result transformer will need to understand how to detect and deal with the different result format from a wildcard read-resource (result is a LIST of OBJECT) versus a simple read-resource (just an OBJECT).

It's better if the filtering is done as soon as possible (to save the cost of transmitting data from servers to slaves to the DC just so the DC can filter) but for this mixed domain case I think it's ok to send the full read-resource result back to the DC.