Building a new data model library with CMake

PODIO exposes multiple CMake macros to enable the building of data model libraries. For a package developer tutorial on CMake, please have a look here. PODIO follows the same conventions used therein.

Exported CMake functions and macros

The file cmake/podioMacros.cmake provides the following functions for external use:

PODIO_GENERATE_DATAMODEL - generate the data model from provided yaml file
PODIO_ADD_DATAMODEL_CORE_LIB - compile the generated data model
PODIO_ADD_ROOT_IO_DICT - configure ROOT I/O backend and interface to Python
PODIO_ADD_SIO_IO_BLOCKS - configure SIO backend

Their exact parameters and functionality are documented in the file mentioned above. Below a few examples.

A simple example

After a proper find_package(podio REQUIRED), the C++ code of the new data model newdm can be created and compiled via

# generate the c++ code from the yaml definition
PODIO_GENERATE_DATAMODEL(newdm newdm.yaml headers sources)

# compile the core data model shared library (no I/O)
PODIO_ADD_DATAMODEL_CORE_LIB(newdm "${headers}" "${sources}")

# generate and compile the ROOT I/O dictionary for the default I/O system
PODIO_ADD_ROOT_IO_DICT(newdmDict newmdm "${headers}" src/selection.xml)

For an explicit choice of I/O backends one needs to add the IO_BACKEND_HANDLERS parameter and then generate and compile the corresponding backends, like shown below for the ROOT and SIO backends:

# generate the c++ code from the yaml definition
PODIO_GENERATE_DATAMODEL(newdm newdm.yaml headers sources IO_BACKEND_HANDLERS "ROOT;SIO")

# compile the core data model shared library (no I/O)
PODIO_ADD_DATAMODEL_CORE_LIB(newdm "${headers}" "${sources}")

# generate and compile the ROOT I/O dictionary for the default I/O system
PODIO_ADD_ROOT_IO_DICT(newdmDict newmdm "${headers}" src/selection.xml)

# compile the SIOBlocks shared library for the SIO backend
PODIO_ADD_SIO_IO_BLOCKS(newdm "${headers}" "${sources}")

For a complete example, please have a look at EDM4hep