if-has-value

The if-has-value Instruction conditionally executes a nested lists of Instructions depending on whether a Destination has a value set. This is useful for setting default values.

action "if-has-value"
destination The Destination to check.
name The Name within the Destination.
then An array of Instructions to be executed when the value exists in the Destination (optional).
else An array of Instructions to be executed when the value does not exist in the Destination (optional).

See also if-exists.

Example: setting defaults

To ensure a object always has a title by applying a default if no other value has been set, add this to the end of your control file’s Instructions.

{
    "action": "if-has-value",
    "destination": "book",
    "name": "dc:attribute:title",
    "else": [
        {
            "action": "set-value",
            "destination": "book",
            "name": "dc:attribute:title",
            "value": "Unnamed project"
        }
    ]
}