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I want to make a copy of an ActiveRecord object, changing a single field in the process (in addition to the id). What is the simplest way to accomplish this?
I realize I could create a new record, and then iterate over each of the fields copying the data field-by-field - but I figured there must be an easier way to do this.
Perhaps something like this:
new_record = Record.copy(:id) 
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You generally use #clone if you want to copy an object including its internal state. This is what Rails is using with its #dup method on ActiveRecord. It uses #dup to allow you to duplicate a record without its "internal" state (id and timestamps), and leaves #clone up to Ruby to implement.
The Ruby docs for dup say: In general, clone and dup may have different semantics in descendent classes. While clone is used to duplicate an object, including its internal state, dup typically uses the class of the descendent object to create the new instance.
ActiveRecord is an ORM. It's a layer of Ruby code that runs between your database and your logic code. When you need to make changes to the database, you'll write Ruby code, and then run "migrations" which makes the actual changes to the database.
Active Record is the M in MVC - the model - which is the layer of the system responsible for representing business data and logic. Active Record facilitates the creation and use of business objects whose data requires persistent storage to a database.
To get a copy, use the dup (or clone for < rails 3.1+) method:
#rails >= 3.1 new_record = old_record.dup # rails < 3.1 new_record = old_record.clone Then you can change whichever fields you want.
ActiveRecord overrides the built-in Object#clone to give you a new (not saved to the DB) record with an unassigned ID.
Note that it does not copy associations, so you'll have to do this manually if you need to.
Rails 3.1 clone is a shallow copy, use dup instead...
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