What methods can be used to control and respond to data changes in a database?

Control and reaction to data changes in a database in C# can be implemented in several ways:

1. Database triggers — special procedures that automatically execute when data is changed (INSERT, UPDATE, DELETE). They allow for logic to be executed directly in the database, such as auditing.

2. Repository pattern with change tracking — in the application, a data access layer can be implemented that tracks object changes and reacts to them.

3. Entity Framework (EF) events — if EF is used, you can subscribe to SavingChanges, SavedChanges events to handle changes before or after saving.

4. Change Tracking and Change Detection — EF can track changes in entities, allowing for programmatic reactions.

5. Using the Observer pattern or events in code — when data changes in the application, events can be generated that other components subscribe to.

Example with EF Core:

context.SavingChanges += (sender, args) => {
    var changedEntities = context.ChangeTracker.Entries()
        .Where(e => e.State == EntityState.Modified || e.State == EntityState.Added || e.State == EntityState.Deleted);
    foreach (var entity in changedEntities)
    {
        // Logic to handle changes
    }
};

Thus, the choice of method depends on the application's architecture and the requirements for reacting to changes.