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[ntuple] allow for writing into TFile subdir (WIP) #16838

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[ntuple] allow for writing into TFile subdir (WIP) #16838

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3 changes: 3 additions & 0 deletions tree/ntuple/v7/inc/ROOT/RMiniFile.hxx
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,7 @@ class RNTupleFileWriter {
private:
struct RFileProper {
TFile *fFile = nullptr;
std::string fDirectory;
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Either

Suggested change
std::string fDirectory;
TDirectory* fDirectory;

or

Suggested change
std::string fDirectory;
std::string fDirectoryPath;

/// Low-level writing using a TFile
void Write(const void *buffer, size_t nbytes, std::int64_t offset);
/// Writes an RBlob opaque key with the provided buffer as data record and returns the offset of the record
Expand Down Expand Up @@ -178,6 +179,8 @@ private:

explicit RNTupleFileWriter(std::string_view name, std::uint64_t maxKeySize);

static std::pair<std::string_view, std::string_view> SplitNTupleName(std::string_view nameAndDir);

/// For a TFile container written by a C file stream, write the header and TFile object
void WriteTFileSkeleton(int defaultCompression);
/// The only key that will be visible in file->ls()
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21 changes: 19 additions & 2 deletions tree/ntuple/v7/src/RMiniFile.cxx
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Expand Up @@ -1105,12 +1105,27 @@ ROOT::Experimental::Internal::RNTupleFileWriter::Recreate(std::string_view ntupl
return writer;
}

std::pair<std::string_view, std::string_view> ROOT::Experimental::Internal::RNTupleFileWriter::SplitNTupleName(
std::string_view nameAndDir)
{
const auto posLastSlash = nameAndDir.find_last_of('/');
if (posLastSlash == std::string::npos)
return std::make_pair("", nameAndDir);

if (posLastSlash == nameAndDir.size() - 1)
throw RException(R__FAIL("empty RNTuple name"));

return std::make_pair(nameAndDir.substr(0, posLastSlash), nameAndDir.substr(posLastSlash + 1));
}

std::unique_ptr<ROOT::Experimental::Internal::RNTupleFileWriter>
ROOT::Experimental::Internal::RNTupleFileWriter::Append(std::string_view ntupleName, TFile &file,
std::uint64_t maxKeySize)
{
auto writer = std::unique_ptr<RNTupleFileWriter>(new RNTupleFileWriter(ntupleName, maxKeySize));
auto [dir, name] = SplitNTupleName(ntupleName);
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@pcanal pcanal Nov 6, 2024 •
edited
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Note that it would also be nice to have:

ROOT::Experimental::Internal::RNTupleFileWriter::Append(std::string_view ntupleName, TDIrectory &dir,
                                                        std::uint64_t maxKeySize) 
{
     if (!dir.GetFile())
        throw "We need a file";
   auto writer = std::unique_ptr<RNTupleFileWriter>(new RNTupleFileWriter(name, maxKeySize));
   writer->fFileProper.fFile = dir->GetFile();
   writer->fFileProper.fDirectory = &dir;

(oups the type of fDirectory is wrong).

auto writer = std::unique_ptr<RNTupleFileWriter>(new RNTupleFileWriter(name, maxKeySize));
writer->fFileProper.fFile = &file;
writer->fFileProper.fDirectory = dir;
return writer;
}

Expand All @@ -1124,7 +1139,9 @@ void ROOT::Experimental::Internal::RNTupleFileWriter::Commit()
{
if (fFileProper) {
// Easy case, the ROOT file header and the RNTuple streaming is taken care of by TFile
fFileProper.fFile->WriteObject(&fNTupleAnchor, fNTupleName.c_str());
auto dir = fFileProper.fFile->GetDirectory(fFileProper.fDirectory.c_str());
dir->cd();
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A priori the cd is not needed. If it is then we need to use also a TDirectory::TContext to make the function have no net effect on gDirectory.

dir->WriteObject(&fNTupleAnchor, fNTupleName.c_str());

// Make sure the streamer info records used in the RNTuple are written to the file
TBufferFile buf(TBuffer::kWrite);
Expand Down
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