A sample is the unit of data exchanged between writers and readers. It provides multiple data members which are accessed with get accessor methods.

On this page:

Key and value

The sample key and value can be obtained by calling the getKey and getValue methods. If no value is available (if the sample event is Remove for example), a default value is returned. You should check the sample event before getting the value to ensure the sample has a value.

Event

The getEvent method returns the sample event enumeration value. The SampleEvent enum definition is:

enum class SampleEvent : unsigned char
{
    Add,
    Update,
    PartialUpdate,
    Remove
};

If the event is Remove, the sample value will be a default value.

If it's PartialUpdate, the sample also provides the update tag with the getUpdateTag method. The value returned by getValue for a PartialUpdate event is the value computed after applying the partial update using the updater identified by the update tag. If no updater is setup for the update tag, the partial update isn't applied leaving the value unchanged.

Timestamp, origin and session

The getTimestamp method returns a std::chrono::time_point<std::chrono::system_clock> value. It's set by the writer to the sending time of the sample.

The origin of the sample returned by getOrigin is the name of the writer that published the sample. It's only available with samples returned by a reader. If no explicit writer name was set on writer creation, a unique name is generated by DataStorm.

The getSession method returns an identifier to identify the session established between the two nodes that exchanged the sample. This session identifier can be used to retrieve the Ice connection using the node getSessionConnection method.