Frames API to write collection metadata?

[veprbl]

It used to be possible to write metadata for collections with EventStore:

podio/tests/write_test.h

Lines 92 to 93 in c7328d6

	auto& colMD = store.getCollectionMetaData(hits.getID());
	colMD.setValue("CellIDEncodingString", "system:8,barrel:3,layer:6,slice:5,x:-16,y:-16");

Is there a way to do this for Frames?

[tmadlener]

Not yet as conveniently, I am afraid. We are planning to have comparable functionality, but we are not yet entirely sure how to best implement it.

The two ideas that we have in mind are along these lines:

• Store collection meta data as part of the Frame parameters for each Frame and then add something along the lines of the following to the Frame interface

template<typename T>
auto getCollectionParameter(const std::string& parName, const podio::CollectionBase& coll);

• Alternatively we create a dedicated collection parameter Frame (implicitly handled by podio potentially), and give the collections a means to effectively pick up its parameters from there. This would make it possible to have the parameters as part of the collection interface, but hooking this up internally is not entirely trivial.

[hegner]

actually this is currently a blocker for the Frame migration in k4FWCore.
(and it should never have ended up in the DataHandle in the first place :-( )