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NOTE

The information contained in this document represents information about preview features of the product. Features might change when the product is released for general availability.

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Container Class API

The Direct Access Classes implement a reader and a writer class which provides zero-copy reads and direct references to related records. This allows you to cache values in a local variable without the overhead of performing copy every time you read a field value.

The following are exposed as part of the container patient _list_t.

Examples in these articles are taken from the Direct Access sample app that is installed with the SDK at /opt/gaia/examples/direct_access.

patients_t::list()

Methods on the container

insert

patients_t::insert() - Creates a relationship between the rows.

insert() has two overrides:

• One that accepts a gaia_id_t, which isn't typesafe, and avoids the creation of objects if you already have the Gaia id.
• One that accepts an instance of a Direct Access class, which is typesafe, and does not allow passing instances of the wrong type.

Synonym for disconnect().

remove

patients_t::[list_name]().remove()

Breaks a relationship between rows.

Synonym for disconnect().

connect

patients_t::[list_name]().connect()

Synonym for connect().

disconnect

patients_t::[list_name]().disconnect()

Aliased to remove.

clear

patients_t::[list_name]().clear()

Removes all relationships (1 side of 1:1 or N side of 1:N) from this reference.

erase

patients_t::[list_name]().erase()

The erase() method is functionally the equivalent to the disconnect() method except that it takes an iterator that points to the item to disconnect and returns an iterator to the next item in the list.

size

patients_t::[list_name]().size()

Gets the number of linked rows.

Example

patient_t jane = patient_t::get(patient_t::insert_row(Jane, 183, true));
address_t kissimmee = address_t::get(address_t::insert_row(Hamlet Ln, Kissimmee));
jane.address().connect(kissimmee);

// You can also pass the id:
jane.address().connect(kissimmee.gaia_id());
void delete_one_to_many_relationship(gaia_id_t doctor_id)
{
    PRINT_METHOD_NAME();
    doctor_t doctor = doctor_t::get(doctor_id);
    
    // Pick one of the doctor\'s patients.
    patient_t patient = *(doctor.patients().begin());
    
    // You can unlink a single element (there are still 2 connected).
    doctor.patients().remove(patient);
    
    // You can now delete the patient.
    patient.delete_row();
    
    // Unlink all the remaining patients.
    doctor.patients().clear();
    
    // You can now delete the doctor.
    doctor.delete_row();
}

Methods on Value Linked References

patients_t::list().begin()

patients_t::list().end()

patients_t::list().where()

The where() takes a predicate as input and returns a container with the filtered elements as output. The predicate is expressed as std::function bool (const > T_class&) where the T_class is the Direct Access class contained by the container.

edc_invalid_object_type: Argument does not match the class type.

Example

// Contains with expression.
auto jacks_doctor_container = doctor_t::list().where(
doctor_expr::patients.contains(
patient_expr::name == Jack));
auto jacks_doctor = *jacks_doctor_container.begin();
gaia_log::app().info("Jack's doctor is {}", jacks_doctor.name());

// Contains with constant.
auto jane = *(patient_t::list().where(patient_expr::name ==Jane).begin());
auto janes_doctor_container = doctor_t::list().where(
doctor_expr::patients.contains(jane));
auto janes_doctor = *janes_doctor_container.begin();
gaia_log::app().info("Jane's doctor is {}", janes_doctor.name());
auto doctors_with_no_patients =
    doctor_t::list().where(doctor_expr::patients.empty());

if (doctors_with_no_patients.begin() == doctors_with_no_patients.end())
{
    gaia_log::app().info(All the doctors have at least one patient);
}
...

Operators on containers

The following methods are used to evaluate predicates on relationships.

contains

contains()

Evaluates to true when at least one object in the container matches a filter predicate.

empty

empty()

Evaluates to true if a container is empty.

count

count()

Evaluates to true when a container contains the specified number of elements.

Example

The following code snippet shows the usage of the contains() and empty() methods.

// Contains with expression.
auto jacks_doctor_container = doctor_t::list().where(
    doctor_expr::patients.contains(patient_expr::name == Jack));
auto jacks_doctor = *jacks_doctor_container.begin();
gaia_log::app().info("Jack's doctor is {}", jacks_doctor.name());

// Contains with constant.
auto jane = *(patient_t::list().where(patient_expr::name == Jane).begin());
auto janes_doctor_container = doctor_t::list().where(
    doctor_expr::patients.contains(jane));
auto janes_doctor = \janes_doctor_container.begin();
gaia_log::app().info("Jane's doctor is {}", janes_doctor.name());
auto doctors_with_no_patients =
    doctor_t::list().where(doctor_expr::patients.empty());
...