File ROOTReader.h

namespace podio

class ROOTReader

#include <podio/ROOTReader.h>

This class has the function to read available data from disk in ROOTs TTree format.

The ROOTReader provides the data as ROOTFrameData from which a podio::Frame can be constructed. It can be used to read files written by the ROOTWriter.

Public Functions

ROOTReader() = default

Create a ROOTReader.

~ROOTReader() = default

Destructor.

ROOTReader(const ROOTReader&) = delete

The ROOTReader is not copy-able.

ROOTReader &operator=(const ROOTReader&) = delete

The ROOTReader is not copy-able.

void openFile(const std::string &filename)

Open a single file for reading.

Parameters:

filename – The name of the input file

void openFiles(const std::vector<std::string> &filenames)

Open multiple files for reading and then treat them as if they are one file.

Note

All of the files are assumed to have the same structure. Specifically this means:

• The same categories are available from all files

• The collections that are contained in the individual categories are the same across all files

• This usually boils down to “the files have been written with the same

  ”settings”, e.g. they are outputs of a batched process.

Parameters:

filenames – The filenames of all input files that should be read

std::unique_ptr<podio::ROOTFrameData> readNextEntry(const std::string &name)

Read the next data entry for a given category.

Parameters:

name – The category name for which to read the next entry

Returns:

FrameData from which a podio::Frame can be constructed if the category exists and if there are still entries left to read. Otherwise a nullptr

std::unique_ptr<podio::ROOTFrameData> readEntry(const std::string &name, const unsigned entry)

Read the desired data entry for a given category.

Parameters:

• name – The category name for which to read the next entry

• entry – The entry number to read

Returns:

FrameData from which a podio::Frame can be constructed if the category and the desired entry exist. Otherwise a nullptr

unsigned getEntries(const std::string &name) const

Get the number of entries for the given name.

Parameters:

name – The name of the category

Returns:

The number of entries that are available for the category

inline podio::version::Version currentFileVersion() const

Get the build version of podio that has been used to write the current file.

Returns:

The podio build version

std::vector<std::string_view> getAvailableCategories() const

Get the names of all the available Frame categories in the current file(s).

Returns:

The names of the available categories from the file

inline const std::string_view getDatamodelDefinition(const std::string &name) const

Get the datamodel definition for the given name.

Parameters:

name – The name of the datamodel

Returns:

The high level definition of the datamodel in JSON format

inline std::vector<std::string> getAvailableDatamodels() const

Get all names of the datamodels that are available from this reader.

Returns:

The names of the datamodels

Private Functions

void initCategory(CategoryInfo &catInfo, const std::string &name)

Initialize the passed CategoryInfo by setting up the necessary branches, collection infos and all necessary meta data to be able to read entries with this name.

CategoryInfo &getCategoryInfo(const std::string &name)

Get the category information for the given name.

In case there is no TTree with contents for the given name this will return a CategoryInfo with an uninitialized chain (nullptr) member

GenericParameters readEntryParameters(CategoryInfo &catInfo, bool reloadBranches, unsigned int localEntry)

Read the parameters for the entry specified in the passed CategoryInfo.

std::unique_ptr<podio::ROOTFrameData> readEntry(ROOTReader::CategoryInfo &catInfo)

Read the data entry specified in the passed CategoryInfo, and increase the counter afterwards.

In case the requested entry is larger than the available number of entries, return a nullptr.

podio::CollectionReadBuffers getCollectionBuffers(CategoryInfo &catInfo, size_t iColl, bool reloadBranches, unsigned int localEntry)

Get / read the buffers at index iColl in the passed category information.

Private Members

std::unique_ptr<TChain> m_metaChain = {nullptr}

The metadata tree.

std::unordered_map<std::string, CategoryInfo> m_categories = {}

All categories.

std::vector<std::string> m_availCategories = {}

All available categories from this file.

podio::version::Version m_fileVersion = {0, 0, 0}

DatamodelDefinitionHolder m_datamodelHolder = {}

Private Static Functions

template<typename T>
static void readParams(CategoryInfo &catInfo, podio::GenericParameters &params, bool reloadBranches, unsigned int localEntry)

struct CategoryInfo

Helper struct to group together all the necessary state to read / process a given category.

A “category” in this case describes all frames with the same name which are constrained by the ROOT file structure that we use to have the same contents. It encapsulates all state that is necessary for reading from a TTree / TChain (i.e. collection infos, branches, …)

Public Functions

inline CategoryInfo(std::unique_ptr<TChain> &&c)

constructor from chain for more convenient map insertion

Public Members

std::unique_ptr<TChain> chain = {nullptr}

The TChain with the data.

unsigned entry = {0}

The next entry to read.

std::vector<std::pair<std::string, detail::CollectionInfo>> storedClasses = {}

The stored collections in this category.

std::vector<root_utils::CollectionBranches> branches = {}

The branches for this category.

std::shared_ptr<CollectionIDTable> table = {nullptr}

The collection ID table for this category.