Question

Suppose each Project has_many Tasks.

If I do

some_project.tasks = list_of_tasks
some_project.save

The project’s tasks get updated even if the save fails. If list_of_tasks consists of new records, the project’s tasks get deleted even if the save fails! WHOA!

If the save fails, the project should have the same tasks it had before I started messing with it. How do I get this behavior and why isn’t it the default?

Answer 1

Enclose the statements in a transaction:

Project.transaction do
  p.tasks = task_list
  p.save!
end

The save! method throws an exception upon error, which rolls back any changes done to task list.

You can read the documentation if you want to dive a bit more deeply on the subject.