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Implementation of suggestions arising from pmslavin's review #16

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4429433
Automatically fetch catch2 lib!
OliverWoolland Oct 12, 2026
96353c7
Refactor readin/writeout to use nlohmann
OliverWoolland Oct 12, 2026
de6d8eb
Refactor error messages into central defintion
OliverWoolland Oct 12, 2026
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10 changes: 8 additions & 2 deletions CMakeLists.txt
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Open in desktop
Original file line number Diff line number Diff line change
@@ -1,8 +1,9 @@
cmake_minimum_required(VERSION 3.20)
cmake_minimum_required(VERSION 3.24)

project(ro-crate-cpp LANGUAGES CXX)

include(CTest)
include(FetchContent)

add_library(ro-crate-cpp INTERFACE)

Expand All @@ -24,7 +25,12 @@ target_link_libraries(example
)

if(BUILD_TESTING)
find_package(Catch2 3 REQUIRED)
FetchContent_Declare(Catch2
GIT_REPOSITORY https://github.com/catchorg/Catch2.git
GIT_TAG v3.16.0
FIND_PACKAGE_ARGS 3
)
FetchContent_MakeAvailable(Catch2)

add_executable(ro-crate-cpp_tests
tests/integration.cpp
Expand Down
172 changes: 127 additions & 45 deletions include/ro-crate.hpp
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2,15 +2,85 @@

#include <nlohmann/json.hpp>

#include <format>
#include <fstream>
#include <memory>
#include <stdexcept>
#include <string>
#include <string_view>
#include <map>
#include <unordered_map>
#include <vector>

namespace rocrate {

// ---------------------------------------------------------------------------
// Errors
// ---------------------------------------------------------------------------

enum class ErrorCode {
TypesEmpty,
PropertyNameEmpty,
PropertyValueEmpty,
IdPropertyDirectSet,
EntityMissingId,
EntityIdEmpty,
EntityAlreadyExists,
EntityNotFound,
ContextKeyEmpty,
ContextValueEmpty,
FileOpenWriteFailed,
FileOpenReadFailed,
FileParseFailed,
InvalidCrateStructure,
EntityMissingIdField,
EntityMissingTypeField
};

/**
* Returns the message template for the given error code.
* Templates with placeholders are substituted via std::format at the throw site.
*/
constexpr std::string_view error_message(ErrorCode code) {
switch (code) {
case ErrorCode::TypesEmpty:
return "Entity must have at least one type.";
case ErrorCode::PropertyNameEmpty:
return "Property name cannot be empty.";
case ErrorCode::PropertyValueEmpty:
return "Property value cannot be empty.";
case ErrorCode::IdPropertyDirectSet:
return "Cannot set '@id' property directly. "
"Use ROCrate::addEntity to assign an ID.";
case ErrorCode::EntityMissingId:
return "Entity does not have an '@id' property set.";
case ErrorCode::EntityIdEmpty:
return "Entity ID cannot be empty.";
case ErrorCode::EntityAlreadyExists:
return "Entity with id '{}' already exists in the RO-Crate.";
case ErrorCode::EntityNotFound:
return "Entity with id '{}' not found in the RO-Crate.";
case ErrorCode::ContextKeyEmpty:
return "Context key cannot be empty.";
case ErrorCode::ContextValueEmpty:
return "Context value cannot be empty.";
case ErrorCode::FileOpenWriteFailed:
return "Failed to open file for writing: {}";
case ErrorCode::FileOpenReadFailed:
return "Failed to open file for reading: {}";
case ErrorCode::FileParseFailed:
return "Failed to parse JSON from file: {}. Error: {}";
case ErrorCode::InvalidCrateStructure:
return "Invalid RO-Crate structure: missing '@context' or '@graph' fields.";
case ErrorCode::EntityMissingIdField:
return "Entity in RO-Crate JSON is missing '@id' field.";
case ErrorCode::EntityMissingTypeField:
return "Entity in RO-Crate JSON is missing '@type' field.";
}

return "Unknown error";
}

// ---------------------------------------------------------------------------
// Entity
// ---------------------------------------------------------------------------
Expand All @@ -24,7 +94,7 @@ namespace rocrate {
ValueType type;
};

using Properties = std::map<Property, std::vector<PropertyValue>>;
using Properties = std::unordered_map<Property, std::vector<PropertyValue>>;

/**
* Represents an entity in the RO-Crate.
Expand Down Expand Up @@ -87,7 +157,7 @@ namespace rocrate {

// Validate types (reject empty)
if ( types.empty() ) {
throw std::invalid_argument("Entity must have at least one type.");
throw std::invalid_argument(std::string(error_message(ErrorCode::TypesEmpty)));
}

// Set the types of the entity
Expand All @@ -100,12 +170,11 @@ namespace rocrate {
inline void Entity::set(Property property, Value value, ValueType valueType) {
// Validate property and value
if (property.empty())
throw std::invalid_argument("Property name cannot be empty.");
throw std::invalid_argument(std::string(error_message(ErrorCode::PropertyNameEmpty)));
if (value.empty())
throw std::invalid_argument("Property value cannot be empty.");
throw std::invalid_argument(std::string(error_message(ErrorCode::PropertyValueEmpty)));
if (property == "@id")
throw std::invalid_argument("Cannot set '@id' property directly. "
"Use ROCrate::addEntity to assign an ID.");
throw std::invalid_argument(std::string(error_message(ErrorCode::IdPropertyDirectSet)));

// Check property is not duplicate - ignore if so
auto it = properties_->find(property);
Expand All @@ -125,13 +194,13 @@ namespace rocrate {
inline void Entity::set(Property property, const Entity& entity) {
// Validate property name
if (property.empty()) {
throw std::invalid_argument("Property name cannot be empty.");
throw std::invalid_argument(std::string(error_message(ErrorCode::PropertyNameEmpty)));
}

// Check if the entity has an '@id' property set
const auto id = entity.properties_->find("@id");
if (id == entity.properties_->end() || id->second.empty())
throw std::runtime_error("Entity does not have an '@id' property set.");
throw std::runtime_error(std::string(error_message(ErrorCode::EntityMissingId)));

// Add JSON reference to the entity's '@id' to the property in the properties map
set(property, id->second.front().value, ValueType::Reference);
Expand All @@ -140,7 +209,7 @@ namespace rocrate {
inline void Entity::assignId(const std::string& id) {
// Validate id
if (id.empty()) {
throw std::invalid_argument("Entity ID cannot be empty.");
throw std::invalid_argument(std::string(error_message(ErrorCode::EntityIdEmpty)));
}

// Assign the '@id' property to the entity's properties map
Expand All @@ -151,7 +220,7 @@ namespace rocrate {
// RO-Crate
// ---------------------------------------------------------------------------

using EntityRegister = std::map<std::string, Entity>;
using EntityRegister = std::unordered_map<std::string, Entity>;

/**
* Represents an RO-Crate, a structured collection of entities and metadata.
Expand Down Expand Up @@ -215,6 +284,9 @@ namespace rocrate {
void readIn(const std::string& path);

private:
friend void to_json(nlohmann::json& j, const ROCrate& crate);
friend void from_json(const nlohmann::json& j, ROCrate& crate);

nlohmann::json serializeEntity(
const std::string& id,
const Entity& entity
Expand Down Expand Up @@ -261,12 +333,12 @@ namespace rocrate {
inline void ROCrate::addEntity(const std::string& id, Entity& entity) {
// Validate the id (reject empty)
if (id.empty()) {
throw std::invalid_argument("Entity ID cannot be empty.");
throw std::invalid_argument(std::string(error_message(ErrorCode::EntityIdEmpty)));
}

// Check if the entity with the given id already exists in the register
if (entities_.find(id) != entities_.end()) {
throw std::runtime_error("Entity with id '" + id + "' already exists in the RO-Crate.");
if (entities_.contains(id)) {
throw std::runtime_error(std::format(error_message(ErrorCode::EntityAlreadyExists), id));
}

// Add the assigned ID to the Entity itself
Expand All @@ -279,108 +351,118 @@ namespace rocrate {
inline Entity& ROCrate::getEntity(const std::string& id) {
auto it = entities_.find(id);
if (it == entities_.end()) {
throw std::runtime_error("Entity with id '" + id + "' not found in the RO-Crate.");
throw std::runtime_error(std::format(error_message(ErrorCode::EntityNotFound), id));
}
return it->second;
}

inline void ROCrate::addContext(const std::string& key, const std::string& value) {
// Validate the context
if (key.empty()) {
throw std::invalid_argument("Context key cannot be empty.");
throw std::invalid_argument(std::string(error_message(ErrorCode::ContextKeyEmpty)));
}
if (value.empty()) {
throw std::invalid_argument("Context value cannot be empty.");
throw std::invalid_argument(std::string(error_message(ErrorCode::ContextValueEmpty)));
}

// Add the context entry to the RO-Crate's root metadata entity
context_[key] = value;
}

inline void ROCrate::writeOut(const std::string& path) {
nlohmann::json outCrate = *this;


// Write the JSON representation of the RO-Crate to a file
std::ofstream outFile(path);
if (!outFile)
throw std::runtime_error(std::format(error_message(ErrorCode::FileOpenWriteFailed), path));

outFile << outCrate.dump(4); // Pretty print with 4 spaces indentation
}

inline void to_json(nlohmann::json& j, const ROCrate& crate) {
// Create the JSON representation of the RO-Crate
nlohmann::json outCrate = {
j = {
{"@context", "https://w3id.org/ro/crate/1.3/context"},
{"@graph", nlohmann::json::array()}
};

// Add the context entries to the JSON representation
if (!context_.empty()) {
outCrate["@context"] = nlohmann::json::array();
outCrate["@context"].push_back("https://w3id.org/ro/crate/1.3/context");
for (const auto& [key, value] : context_) {
outCrate["@context"].push_back({{key, value}});
if (!crate.context_.empty()) {
j["@context"] = nlohmann::json::array();
j["@context"].push_back("https://w3id.org/ro/crate/1.3/context");
for (const auto& [key, value] : crate.context_) {
j["@context"].push_back({{key, value}});
}
}

// Iterate over the entities, conver to json and append to the graph
for (const auto& [id, entity] : entities_) {
outCrate["@graph"].push_back(serializeEntity(id, entity));
for (const auto& [id, entity] : crate.entities_) {
j["@graph"].push_back(crate.serializeEntity(id, entity));
}

// Write the JSON representation of the RO-Crate to a file
std::ofstream outFile(path);
if (!outFile)
throw std::runtime_error("Failed to open file for writing: " + path);

outFile << outCrate.dump(4); // Pretty print with 4 spaces indentation
}

inline void ROCrate::readIn(const std::string& path) {
// Read the JSON representation of the RO-Crate from a file
std::ifstream inFile(path);
if (!inFile)
throw std::runtime_error("Failed to open file for reading: " + path);
throw std::runtime_error(std::format(error_message(ErrorCode::FileOpenReadFailed), path));

// Check if valid JSON
nlohmann::json inCrate;
try {
inFile >> inCrate;
} catch (const nlohmann::json::parse_error& e) {
throw std::runtime_error("Failed to parse JSON from file: " + path + ". Error: " + e.what());
throw std::runtime_error(std::format(error_message(ErrorCode::FileParseFailed), path, e.what()));
}

// Validate the RO-Crate structure and populate the current instance
from_json(inCrate, *this);
}

inline void from_json(const nlohmann::json& j, ROCrate& crate) {
// Validate the RO-Crate structure
if (!inCrate.contains("@context") || !inCrate.contains("@graph")) {
throw std::runtime_error("Invalid RO-Crate structure in file: " + path);
if (!j.contains("@context") || !j.contains("@graph")) {
throw std::runtime_error(std::string(error_message(ErrorCode::InvalidCrateStructure)));
}

// Upsert the context entries from the JSON representation into the RO-Crate
if (inCrate["@context"].is_array()) {
for (const auto& contextEntry : inCrate["@context"]) {
if (j["@context"].is_array()) {
for (const auto& contextEntry : j["@context"]) {
if (contextEntry.is_object()) {
for (const auto& [key, value] : contextEntry.items()) {
addContext(key, value.get<std::string>());
crate.addContext(key, value.get<std::string>());
}
}
}
}

// Iterate over the entities in the JSON representation and add them to the RO-Crate
for (const auto& entityJson : inCrate["@graph"]) {
for (const auto& entityJson : j["@graph"]) {
// Validate that the entity has an '@id' field
if (!entityJson.contains("@id")) {
throw std::runtime_error("Entity in RO-Crate JSON is missing '@id' field.");
throw std::runtime_error(std::string(error_message(ErrorCode::EntityMissingIdField)));
}
std::string entityId = entityJson["@id"].get<std::string>();

// Get the entity type
if (!entityJson.contains("@type")) {
throw std::runtime_error("Entity in RO-Crate JSON is missing '@type' field.");
throw std::runtime_error(std::string(error_message(ErrorCode::EntityMissingTypeField)));
}
std::string entityType = entityJson["@type"].get<std::string>();

// Try getting the entity from the register, if it exists, otherwise create a new one
Entity entity({"Thing"}); // Default type, will be overridden if entity exists
try {
// Existing entity
entity = getEntity(entityId);
updateProperties(entity, entityJson);
entity = crate.getEntity(entityId);
crate.updateProperties(entity, entityJson);
} catch (const std::runtime_error&) {
// Entity does not exist, create a new one
entity = Entity({entityType});
updateProperties(entity, entityJson);
addEntity(entityId, entity);
crate.updateProperties(entity, entityJson);
crate.addEntity(entityId, entity);
}
}
}
Expand Down