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Goal

I am trying to store an edm4hep file using RDataFrame::Snapshot after applying some cuts.
For columns (branches?) of type edm4hep::ReconstructedParticleData this seems to just work.
However, for e.g. the corresponding clusters (_CollectionName_clusters) of type podio::ObjectID, I get the error:

Error in <TTree::Branch>: The class requested (ROOT::VecOps::RVec<podio::ObjectID>) for the branch "_CollectionName_clusters" is an instance of an stl collection and does not have a compiled CollectionProxy. Please generate the dictionary for this collection (ROOT::VecOps::RVec<podio::ObjectID>) to avoid to write corrupted data.
RDataFrame::Run: event loop was interrupted

Operating System and Version

Alma Linux 9

compiler

necessary?

The version of the key4hep stack

source /cvmfs/sw.hsf.org/key4hep/setup.sh -r 2025-01-28

Package Version

whatever is in the above release

Reproducer

import ROOT

df = ROOT.RDataFrame("events", "https://lreichen.webtest.cern.ch/minidst.edm4hep.root")
# doesn't work
# df.Range(10).Snapshot("events", "snapshot-test.root", ["_BCalRecoParticle_clusters"])
# works
df.Range(10).Snapshot("events", "snapshot-test.root", ["BCalRecoParticle"])
print(df.GetColumnType("_BCalRecoParticle_clusters"))
# ROOT::VecOps::RVec<podio::ObjectID>
print(df.GetColumnType("BCalRecoParticle"))
# ROOT::VecOps::RVec<edm4hep::ReconstructedParticleData>

Additional context

I am honestly more confused that one of the two cases works.
As far as I know, ROOT needs to have RVec<type> in the dictionary for RVecs to be written out; vector<type> is not enough and as far as I can tell, we only have the latter in edm4hepDictDict.rootmap and podioDictDict.rootmap. But this is where my knowledge of ROOT dictionaries ends.

It would, of course, be even better if ROOT would not automatically convert everything to RVecs when writing a Snapshot, but we don't have a new enough version for this in the stack... :)
root-project/root#15895