Transactions {#transactions}

Using a transaction for lights

Often, you want to change more than one variable on a light at the same time, for example brightness and color. This is done using transactions (StateTransaction).

light.transaction().setOn(true).setBrightness(29).setColorHue(3000).setColorSaturation(128).commit();

The request is reduced to only the variables that need to be changed based on the current state. For example, if the light is already on, that part of the transaction is ignored.

Important: The transaction has an internal reference to the light state. You must not cause a refresh of the state between creating and committing the transaction (e.g. non-const getters/setters), because that invalidates the reference.

Advanced usage

Another way to use the transaction is by storing it and building up the calls separately.

hueplusplus::StateTransaction t = light.transaction();
if(shouldTurnOn)
    t.setOn(true);
t.commit();

In this case, it is especially important that the light and the state of the light MUST NOT invalidate. That means

• the light variable has to live longer than the transaction
• especially no non-const method calls on the light while the transaction is open, or committing other transactions

In general, this method is easier to screw up and should only be used when really necessary.

Using a transaction for groups

The same principles of transactions for lights also apply for groups. The main difference is that for groups, there are no checks of the current state. Even if all lights in the group are already on, the request to turn on all lights on the group is still sent.

group.transaction().setOn(true).setBrightness(64).commit();

Creating Actions

In a Schedule or Rule, the bridge can set the state of lights and groups. To configure this, a transaction can be saved for later instead of committing it directly.

hueplusplus::Action action = light.transaction().setOn(true).setBrightness(255).toAction();
schedule.setCommand(action);