RNTupleModel.hxx

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/// \file ROOT/RNTupleModel.hxx
/// \ingroup NTuple ROOT7
/// \author Jakob Blomer <jblomer@cern.ch>
/// \date 2018-10-04
/// \warning This is part of the ROOT 7 prototype! It will change without notice. It might trigger earthquakes. Feedback
/// is welcome!
 
/*************************************************************************
 * Copyright (C) 1995-2019, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/
 
#ifndef ROOT7_RNTupleModel
#define ROOT7_RNTupleModel
 
#include <ROOT/REntry.hxx>
#include <ROOT/RError.hxx>
#include <ROOT/RField.hxx>
#include <ROOT/RNTupleUtil.hxx>
#include <string_view>
 
#include <cstdint>
#include <functional>
#include <memory>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
 
namespace ROOT {
namespace Experimental {
 
class RNTupleModel;
class RNTupleWriter;
class RNTupleWriteOptions;
 
namespace Internal {
class RProjectedFields;
 
RFieldZero &GetFieldZeroOfModel(RNTupleModel &model);
RProjectedFields &GetProjectedFieldsOfModel(RNTupleModel &model);
 
// clang-format off
/**
\class ROOT::Experimental::Internal::RProjectedFields
\ingroup NTuple
\brief The projected fields of a `RNTupleModel`
 
Projected fields are fields whose columns are reused from existing fields. Projected fields are not attached
to the models zero field.  Only the real source fields are written to, projected fields are stored as meta-data
(header) information only.  Only top-level projected fields are supported because otherwise the layout of types
could be altered in unexpected ways.
All projected fields and the source fields used to back them are kept in this class.
*/
// clang-format on
class RProjectedFields {
public:
   /// The map keys are the projected target fields, the map values are the backing source fields
   /// Note that sub fields are treated individually and indepently of their parent field
   using FieldMap_t = std::unordered_map<const RFieldBase *, const RFieldBase *>;
 
private:
   explicit RProjectedFields(std::unique_ptr<RFieldZero> fieldZero) : fFieldZero(std::move(fieldZero)) {}
   /// The projected fields are attached to this zero field
   std::unique_ptr<RFieldZero> fFieldZero;
   /// Maps the source fields from fModel to the target projected fields attached to fFieldZero
   FieldMap_t fFieldMap;
   /// The model this set of projected fields belongs to
   const RNTupleModel *fModel;
 
   /// Asserts that the passed field is a valid target of the source field provided in the field map.
   /// Checks the field without looking into sub fields.
   RResult<void> EnsureValidMapping(const RFieldBase *target, const FieldMap_t &fieldMap);
 
public:
   explicit RProjectedFields(const RNTupleModel &model) : fFieldZero(std::make_unique<RFieldZero>()), fModel(&model) {}
   RProjectedFields(const RProjectedFields &) = delete;
   RProjectedFields(RProjectedFields &&) = default;
   RProjectedFields &operator=(const RProjectedFields &) = delete;
   RProjectedFields &operator=(RProjectedFields &&) = default;
   ~RProjectedFields() = default;
 
   /// The new model needs to be a clone of fModel
   std::unique_ptr<RProjectedFields> Clone(const RNTupleModel &newModel) const;
 
   RFieldZero &GetFieldZero() { return *fFieldZero; }
   const RFieldBase *GetSourceField(const RFieldBase *target) const;
   /// Adds a new projected field. The field map needs to provide valid source fields of fModel for 'field'
   /// and each of its sub fields.
   RResult<void> Add(std::unique_ptr<RFieldBase> field, const FieldMap_t &fieldMap);
   bool IsEmpty() const { return fFieldZero->begin() == fFieldZero->end(); }
};
 
// clang-format off
/**
\class ROOT::Experimental::Internal::RNTupleModelChangeset
\ingroup NTuple
\brief The incremental changes to a `RNTupleModel`
 
Represents a set of alterations to a `RNTupleModel` that happened after the model is used to initialize a `RPageSink`
instance. This object can be used to communicate metadata updates to a `RPageSink`.
You will not normally use this directly; see `RNTupleModel::RUpdater` instead.
*/
// clang-format on
struct RNTupleModelChangeset {
   RNTupleModel &fModel;
   /// Points to the fields in fModel that were added as part of an updater transaction
   std::vector<RFieldBase *> fAddedFields;
   /// Points to the projected fields in fModel that were added as part of an updater transaction
   std::vector<RFieldBase *> fAddedProjectedFields;
 
   RNTupleModelChangeset(RNTupleModel &model) : fModel(model) {}
   bool IsEmpty() const { return fAddedFields.empty() && fAddedProjectedFields.empty(); }
};
 
} // namespace Internal
 
// clang-format off
/**
\class ROOT::Experimental::RNTupleModel
\ingroup NTuple
\brief The RNTupleModel encapulates the schema of an ntuple.
 
The ntuple model comprises a collection of hierarchically organized fields. From a model, "entries"
can be extracted. For convenience, the model provides a default entry unless it is created as a "bare model".
Models have a unique model identifier that faciliates checking whether entries are compatible with it
(i.e.: have been extracted from that model).
 
A model is subject to a state transition during its lifetime: it starts in a building state, in which fields can be
added and modified.  Once the schema is finalized, the model gets frozen.  Only frozen models can create entries.
*/
// clang-format on
class RNTupleModel {
   friend RFieldZero &Internal::GetFieldZeroOfModel(RNTupleModel &);
   friend Internal::RProjectedFields &Internal::GetProjectedFieldsOfModel(RNTupleModel &);
 
public:
   /// User provided function that describes the mapping of existing source fields to projected fields in terms
   /// of fully qualified field names. The mapping function is called with the qualified field names of the provided
   /// field and the subfields.  It should return the qualified field names used as a mapping source.
   using FieldMappingFunc_t = std::function<std::string(const std::string &)>;
 
   /// A wrapper over a field name and an optional description; used in `AddField()` and `RUpdater::AddField()`
   struct NameWithDescription_t {
      NameWithDescription_t(const char *name) : fName(name) {}
      NameWithDescription_t(const std::string &name) : fName(name) {}
      NameWithDescription_t(std::string_view name) : fName(name) {}
      NameWithDescription_t(std::string_view name, std::string_view descr) : fName(name), fDescription(descr) {}
 
      std::string_view fName;
      std::string_view fDescription = "";
   };
 
   /// A model is usually immutable after passing it to an `RNTupleWriter`. However, for the rare
   /// cases that require changing the model after the fact, `RUpdater` provides limited support for
   /// incremental updates, e.g. addition of new fields.
   ///
   /// See `RNTupleWriter::CreateModelUpdater()` for an example.
   class RUpdater {
   private:
      RNTupleWriter &fWriter;
      Internal::RNTupleModelChangeset fOpenChangeset;
      std::uint64_t fNewModelId = 0; ///< The model ID after committing
 
   public:
      explicit RUpdater(RNTupleWriter &writer);
      ~RUpdater() { CommitUpdate(); }
      /// Begin a new set of alterations to the underlying model. As a side effect, all `REntry` instances related to
      /// the model are invalidated.
      void BeginUpdate();
      /// Commit changes since the last call to `BeginUpdate()`. All the invalidated `REntry`s remain invalid.
      /// `CreateEntry()` or `CreateBareEntry()` can be used to create an `REntry` that matching the new model.
      /// Upon completion, `BeginUpdate()` can be called again to begin a new set of changes.
      void CommitUpdate();
 
      template <typename T, typename... ArgsT>
      std::shared_ptr<T> MakeField(const NameWithDescription_t &fieldNameDesc, ArgsT &&...args)
      {
         auto objPtr = fOpenChangeset.fModel.MakeField<T>(fieldNameDesc, std::forward<ArgsT>(args)...);
         auto fieldZero = fOpenChangeset.fModel.fFieldZero.get();
         auto it = std::find_if(fieldZero->begin(), fieldZero->end(),
                                [&](const auto &f) { return f.GetFieldName() == fieldNameDesc.fName; });
         R__ASSERT(it != fieldZero->end());
         fOpenChangeset.fAddedFields.emplace_back(&(*it));
         return objPtr;
      }
 
      void AddField(std::unique_ptr<RFieldBase> field);
 
      RResult<void> AddProjectedField(std::unique_ptr<RFieldBase> field, FieldMappingFunc_t mapping);
   };
 
private:
   /// Hierarchy of fields consisting of simple types and collections (sub trees)
   std::unique_ptr<RFieldZero> fFieldZero;
   /// Contains field values corresponding to the created top-level fields, as well as registered subfields
   std::unique_ptr<REntry> fDefaultEntry;
   /// Keeps track of which field names are taken, including projected field names.
   std::unordered_set<std::string> fFieldNames;
   /// Free text set by the user
   std::string fDescription;
   /// The set of projected top-level fields
   std::unique_ptr<Internal::RProjectedFields> fProjectedFields;
   /// Keeps track of which subfields have been registered to be included in entries belonging to this model.
   std::unordered_set<std::string> fRegisteredSubfields;
   /// Every model has a unique ID to distinguish it from other models. Entries are linked to models via the ID.
   /// Cloned models get a new model ID.
   std::uint64_t fModelId = 0;
   /// Models have a separate schema ID to remember that the clone of a frozen model still has the same schema.
   std::uint64_t fSchemaId = 0;
   /// Changed by Freeze() / Unfreeze() and by the RUpdater.
   bool fIsFrozen = false;
 
   /// Checks that user-provided field names are valid in the context of this RNTuple model.
   /// Throws an RException for invalid names, empty names (which is reserved for the zero field) and duplicate field
   /// names.
   void EnsureValidFieldName(std::string_view fieldName);
 
   /// Throws an RException if fFrozen is true
   void EnsureNotFrozen() const;
 
   /// Throws an RException if fDefaultEntry is nullptr
   void EnsureNotBare() const;
 
   /// The field name can be a top-level field or a nested field. Returns nullptr if the field is not in the model.
   RFieldBase *FindField(std::string_view fieldName) const;
 
   /// Add a subfield to the provided entry. If `initializeValue` is false, a nullptr will be bound to the entry value
   /// (used in bare models).
   void AddSubfield(std::string_view fieldName, REntry &entry, bool initializeValue = true) const;
 
   RNTupleModel(std::unique_ptr<RFieldZero> fieldZero);
 
public:
   RNTupleModel(const RNTupleModel&) = delete;
   RNTupleModel& operator =(const RNTupleModel&) = delete;
   ~RNTupleModel() = default;
 
   std::unique_ptr<RNTupleModel> Clone() const;
   static std::unique_ptr<RNTupleModel> Create();
   static std::unique_ptr<RNTupleModel> Create(std::unique_ptr<RFieldZero> fieldZero);
   /// A bare model has no default entry
   static std::unique_ptr<RNTupleModel> CreateBare();
   static std::unique_ptr<RNTupleModel> CreateBare(std::unique_ptr<RFieldZero> fieldZero);
 
   /// Creates a new field given a `name` or `{name, description}` pair and a
   /// corresponding value that is managed by a shared pointer.
   ///
   /// **Example: create some fields and fill an %RNTuple**
   /// ~~~ {.cpp}
   /// #include <ROOT/RNTupleModel.hxx>
   /// #include <ROOT/RNTupleWriter.hxx>
   /// using ROOT::Experimental::RNTupleModel;
   /// using ROOT::Experimental::RNTupleWriter;
   ///
   /// #include <vector>
   ///
   /// auto model = RNTupleModel::Create();
   /// auto pt = model->MakeField<float>("pt");
   /// auto vec = model->MakeField<std::vector<int>>("vec");
   ///
   /// // The RNTuple is written to disk when the RNTupleWriter goes out of scope
   /// {
   ///    auto writer = RNTupleWriter::Recreate(std::move(model), "myNTuple", "myFile.root");
   ///    for (int i = 0; i < 100; i++) {
   ///       *pt = static_cast<float>(i);
   ///       *vec = {i, i+1, i+2};
   ///       writer->Fill();
   ///    }
   /// }
   /// ~~~
   ///
   /// **Example: create a field with an initial value**
   /// ~~~ {.cpp}
   /// #include <ROOT/RNTupleModel.hxx>
   /// using ROOT::Experimental::RNTupleModel;
   ///
   /// auto model = RNTupleModel::Create();
   /// // pt's initial value is 42.0
   /// auto pt = model->MakeField<float>("pt", 42.0);
   /// ~~~
   /// **Example: create a field with a description**
   /// ~~~ {.cpp}
   /// #include <ROOT/RNTupleModel.hxx>
   /// using ROOT::Experimental::RNTupleModel;
   ///
   /// auto model = RNTupleModel::Create();
   /// auto hadronFlavour = model->MakeField<float>({
   ///    "hadronFlavour", "flavour from hadron ghost clustering"
   /// });
   /// ~~~
   template <typename T, typename... ArgsT>
   std::shared_ptr<T> MakeField(const NameWithDescription_t &fieldNameDesc, ArgsT &&...args)
   {
      EnsureNotFrozen();
      EnsureValidFieldName(fieldNameDesc.fName);
      auto field = std::make_unique<RField<T>>(fieldNameDesc.fName);
      field->SetDescription(fieldNameDesc.fDescription);
      std::shared_ptr<T> ptr;
      if (fDefaultEntry)
         ptr = fDefaultEntry->AddValue<T>(*field, std::forward<ArgsT>(args)...);
      fFieldNames.insert(field->GetFieldName());
      fFieldZero->Attach(std::move(field));
      return ptr;
   }
 
   /// Adds a field whose type is not known at compile time.  Thus there is no shared pointer returned.
   ///
   /// Throws an exception if the field is null.
   void AddField(std::unique_ptr<RFieldBase> field);
 
   /// Register a subfield so it can be accessed directly from entries belonging to the model. Because registering a
   /// subfield does not fundamentally change the model, previously created entries will not be invalidated, nor
   /// modified in any way; a registered subfield is merely an accessor added to the default entry (if present) and any
   /// entries created afterwards.
   ///
   /// Using models with registered subfields for writing is not allowed. Attempting to do so will result in an
   /// exception.
   ///
   /// Throws an exception if the provided subfield could not be found in the model.
   void RegisterSubfield(std::string_view qualifiedFieldName);
 
   /// Adds a top-level field based on existing fields.
   ///
   /// The mapping function takes one argument, which is a string containing the name of the projected field. The return
   /// value of the mapping function should be the name of the (existing) field onto which the projection is made.
   /// **Example**
   /// ~~~ {.cpp}
   /// auto model = RNTupleModel::Create();
   /// model->MakeField<float>("met");
   /// auto metProjection = RFieldBase::Create("missingE", "float").Unwrap();
   /// model->AddProjectedField(std::move(metProjection), [](const std::string &) { return "met"; });
   /// ~~~
   ///
   /// Adding projections for collection fields is also possible, as long as they follow the same schema structure. For
   /// example, a projection of a collection of structs onto a collection of scalars is possible, but a projection of a
   /// collection of a collection of scalars onto a collection of scalars is not.
   ///
   /// In the case of projections for nested fields, the mapping function must provide a mapping for every nesting
   /// level.
   /// **Example**
   /// ~~~ {.cpp}
   /// struct P { int x, y; };
   ///
   /// auto model = RNTupleModel::Create();
   /// model->MakeField<std::vector<P>>("points");
   /// auto pxProjection = RFieldBase::Create("pxs", "std::vector<int>").Unwrap();
   /// model->AddProjectedField(std::move(pxProjection), [](const std::string &fieldName) {
   ///   if (fieldName == "pxs")
   ///     return "points";
   ///   else
   ///     return "points._0.x";
   /// });
   /// ~~~
   ///
   /// Creating projections for fields containing `std::variant` or fixed-size arrays is unsupported.
   RResult<void> AddProjectedField(std::unique_ptr<RFieldBase> field, FieldMappingFunc_t mapping);
 
   void Freeze();
   void Unfreeze();
   bool IsFrozen() const { return fIsFrozen; }
   bool IsBare() const { return !fDefaultEntry; }
   std::uint64_t GetModelId() const { return fModelId; }
   std::uint64_t GetSchemaId() const { return fSchemaId; }
 
   std::unique_ptr<REntry> CreateEntry() const;
   /// In a bare entry, all values point to nullptr. The resulting entry shall use BindValue() in order
   /// set memory addresses to be serialized / deserialized
   std::unique_ptr<REntry> CreateBareEntry() const;
   /// Creates a token to be used in REntry methods to address a field present in the entry
   REntry::RFieldToken GetToken(std::string_view fieldName) const;
   /// Calls the given field's CreateBulk() method. Throws an exception if no field with the given name exists.
   RFieldBase::RBulk CreateBulk(std::string_view fieldName) const;
 
   REntry &GetDefaultEntry();
   const REntry &GetDefaultEntry() const;
 
   /// Mutable access to the root field is used to make adjustments to the fields.
   RFieldZero &GetMutableFieldZero();
   const RFieldZero &GetConstFieldZero() const { return *fFieldZero; }
   RFieldBase &GetMutableField(std::string_view fieldName);
   const RFieldBase &GetConstField(std::string_view fieldName) const;
 
   const std::string &GetDescription() const { return fDescription; }
   void SetDescription(std::string_view description);
 
   /// Get the (qualified) names of subfields that have been registered to be included in entries from this model.
   const std::unordered_set<std::string> &GetRegisteredSubfields() const { return fRegisteredSubfields; }
 
   /// Estimate the memory usage for this model during writing
   ///
   /// This will return an estimate in bytes for the internal page and compression buffers. The value should be
   /// understood per sequential RNTupleWriter or per RNTupleFillContext created for a RNTupleParallelWriter
   /// constructed with this model.
   std::size_t EstimateWriteMemoryUsage(const RNTupleWriteOptions &options = RNTupleWriteOptions()) const;
};
 
} // namespace Experimental
} // namespace ROOT
 
#endif