1.8. Get entities of a given kind

The StatisticsBackend singleton can be queried about all the entities of a given EntityKind. For example, get_entities() function can be used to retrieve all the HOST for which statistics are reported.

// Get all hosts
std::vector<EntityId> hosts = StatisticsBackend::get_entities(EntityKind::HOST);
for (EntityId host : hosts)
{
    std::cout << "Host ID: " << host << std::endl;
}

This call to get_entities() is the same as:

StatisticsBackend::get_entities(EntityKind::HOST, EntityId::all());

1.8.1. Get entities of a given kind related to another entity

The StatisticsBackend singleton can be queried about all the entities of a given EntityKind that are related to any entity. For example, get_entities() function can be used to retrieve all the PARTICIPANT running on a given HOST.

// Get all participants running in a host
std::vector<EntityId> participants = StatisticsBackend::get_entities(EntityKind::PARTICIPANT, host_id);
for (EntityId participant : participants)
{
    std::cout << "Participant ID: " << participant << std::endl;
}

get_entities() throws BadParameter in the following cases:

• if the EntityKind is INVALID

• if the EntityId does not reference a entity contained in the database or is not EntityId::all().

• if the EntityKind of the EntityId is INVALID

This function returns the related entities according to the following table:

Entity relations

EntityId EntityKind	Host	User	Process	Domain	Topic	DomainParticipant	DataWriter	DataReader	Locator
Host	Itself	Contains	Sub-contains	By DomainParticipant	By DomainParticipant	Sub-contains	Sub-contains	Sub-contains	Sub-contains
User	Contained	Itself	Contains	By DomainParticipant	By DomainParticipant	Sub-contains	Sub-contains	Sub-contains	By Endpoints
Process	Sub-contained	Contained	Itself	By DomainParticipant	By DomainParticipant	Contains	Sub-contains	Sub-contains	By Endpoints
Domain	By DomainParticipant	By DomainParticipant	By DomainParticipant	Itself	Contains	Contains	Sub-contains	Sub-contains	By Endpoints
Topic	By DomainParticipant	By DomainParticipant	By DomainParticipant	Contained	Itself	By Endpoints	Contains	Contains	By Endpoints
DomainParticipant	Sub-contained	Sub-contained	Contained	Contained	By Endpoints	Itself	Contains	Contains	By Endpoints
DataWriter	Sub-contained	Sub-contained	Sub-contained	Sub-contained	Contained	Contained	Itself	By topic	Contains
DataReader	Sub-contained	Sub-contained	Sub-contained	Sub-contained	Contained	Contained	By topic	Itself	Contains
Locator	Sub-contained	By Endpoints	By Endpoints	By Endpoints	By Endpoints	By Endpoints	Contained	Contained	Itself

• Itself: Means that the return will only contain the entity by which the query is performed, i.e. when asking for all the HOST related to a given HOST, the return will simply be the HOST itself.

• Contains: The returned entities will be the ones that the entity by which the query is performed contains, i.e. when asking for all the PARTICIPANT related to a PROCESS, the return will be all the PARTICIPANT that the PROCESS contains.

• Sub-contains: The returned entities will be the ones that the entity by which the query is performed sub-contains, i.e. when asking for all the DATAWRITER related to a USER, the return will be all the DATAWRITER that are contained in each of the PARTICIPANT in each of the PROCESS that the USER contains.

• Contained: The returned entity will be that one in which the entity by which the query is performed is contained, i.e. when asking for all the TOPIC related to a DATAREADER, the return will be the TOPIC in which the DATAREADER is contained.

• Sub-contained: The returned entity will be the one in which the entity by which the query is performed is sub-contained, i.e. when asking for all the HOST related to a PARTICIPANT, the return will be the HOST in which the PARTICIPANT is sub-contained.

• By DomainParticipant: The returned entities will be the ones that are related to the entity by which the query is performed through the DomainParticipant, i.e. when asking for all the HOST related to a DOMAIN, the result will be all the HOST that have a PARTICIPANT running on said DOMAIN.

• By Endpoints: The returned entities will be the ones that are related to the entity by which the query is performed through the endpoints (DATAREADER and DATAWRITER), i.e. when asking for all the LOCATOR related to a TOPIC, the result will be all the LOCATOR that are used by all the DATAREADER and DATAWRITER present in the TOPIC.