DatamodelRegistry.h

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#ifndef PODIO_DATAMODELREGISTRY_H
#define PODIO_DATAMODELREGISTRY_H
 
#include <string>
#include <string_view>
#include <utility>
#include <vector>
 
namespace podio {
 
/**
 * Global registry holding information about datamodels and datatypes defined
 * therein that are currently known by podio (i.e. which have been dynamically
 * loaded).
 *
 * This is a singleton which is (statically) populated during dynamic loading of
 * generated EDMs. In this context an **EDM refers to the shared library** that
 * is compiled from the generated code from a datamodel definition in YAML
 * format. When we refer to a **datamodel** in this context we talk about the
 * entity as a whole, i.e. its definition in a YAML file, but also the concrete
 * implementation as an EDM, as well as all other information that is related to
 * it. In the API of this registry this will be used, unless we want to
 * highlight that we are referring to a specific part of a datamodel.
 */
class DatamodelRegistry {
public:
  /// Get the registry
  static const DatamodelRegistry& instance();
 
  // Mutable instance only used for the initial registration!
  static DatamodelRegistry& mutInstance();
 
  ~DatamodelRegistry() = default;
  DatamodelRegistry(const DatamodelRegistry&) = delete;
  DatamodelRegistry& operator=(const DatamodelRegistry&) = delete;
  DatamodelRegistry(DatamodelRegistry&&) = delete;
  DatamodelRegistry& operator=(const DatamodelRegistry&&) = delete;
 
  /// Dedicated index value for collections that don't have a datamodel
  /// definition (e.g. UserDataCollection)
  static constexpr size_t NoDefinitionNecessary = -1;
  /// Dedicated index value for error checking, used to default init the generated RegistryIndex
  static constexpr size_t NoDefinitionAvailable = -2;
 
  /**
   * Get the definition (in JSON format) of the datamodel with the given
   * edmName.
   *
   * If no datamodel with the given name can be found, an empty datamodel
   * definition, i.e. an empty JSON object ("{}"), is returned.
   *
   * @param name The name of the datamodel
   */
  const std::string_view getDatamodelDefinition(std::string_view name) const;
 
  /**
   * Get the defintion (in JSON format) of the datamodel wth the given index.
   *
   * If no datamodel is found under the given index, an empty datamodel
   * definition, i.e. an empty JSON object ("{}"), is returned.
   *
   * @param index The datamodel definition index that can be obtained from each
   *              collection
   */
  const std::string_view getDatamodelDefinition(size_t index) const;
 
  /**
   * Get the name of the datamodel that is stored under the given index.
   *
   * If no datamodel is found under the given index, an empty string is returned
   *
   * @param index The datamodel definition index that can be obtained from each
   *              collection
   */
  const std::string& getDatamodelName(size_t index) const;
 
  /**
   * Register a datamodel return the index in the registry.
   *
   * This is the hook that is called during dynamic loading of an EDM to
   * register information for this EDM. If an EDM has already been registered
   * under this name, than the index to the existing EDM in the registry will be
   * returned.
   *
   * @param name The name of the EDM that should be registered
   * @param definition The datamodel definition from which this EDM has been
   * generated in JSON format
   *
   */
  size_t registerDatamodel(std::string name, std::string_view definition);
 
private:
  DatamodelRegistry() = default;
  /// The stored definitions
  std::vector<std::pair<std::string, std::string_view>> m_definitions{};
};
} // namespace podio
 
#endif // PODIO_DATAMODELREGISTRY_H