Final answer:
A declarative solution for updating a record when a field changes involves using database triggers, which specify what should happen automatically when a certain database event occurs. For example, an SQL trigger can be created to perform actions on a record update if a specified field value changes, ensuring data integrity and automating business logic.
Step-by-step explanation:
A declarative solution to update a record when the value of a field changes typically involves using a database management system (DBMS) that supports triggers or a similar mechanism. In this context, a declarative solution is one where you specify what should happen, rather than how it should be done. With a trigger, you can define a set of actions that the DBMS will automatically execute when a specified event occurs, such as the modification of a field in a record.
For example, if you are using a SQL database, you could write a trigger like this:
CREATE TRIGGER update_record_trigger
AFTER UPDATE OF target_field ON target_table
FOR EACH ROW
BEGIN
IF OLD.target_field <> NEW.target_field THEN
-- Actions to perform on record update
END IF;
END;
In this trigger, target_field is the field you are monitoring for changes, and target_table is the table containing the record to be updated. The trigger checks if the old value of target_field is different from the new one, and if so, performs the actions defined within the trigger. These actions typically involve updating some other fields or records in response to the change.
This technique is widely used in database-driven applications to maintain data integrity and automate business logic without requiring imperative code that tells the system how to perform each step of the update process. It's more about the intention and the effect rather than the procedural steps.