[erlang-questions] How to upgrade the Mnesia record structure?

[Alexander Alexeev]

On Mon, 03 Jun 2013 06:01:27 +0000
yashgt@REDACTED wrote:

> If a record is defined as:
> 
> -record(shop, {item, quantity, cost}).
> 
> and several records are stored in an Mnesia table, and a few months
> later the structure is changed to : -record(shop, {item, quantity,
> source, company, cost}).
> 
> Do we need to migrate ALL existing records in the DB to include the
> additional 2 elements in the tuple? I know that a record is actually
> a tuple. If we leave the existing records untouched, will the
> database get messed becaues of new records coming in with the new
> structure?
> 
> Thanks,
> Yash

You can also provide a special "extendable" field (call it a backpack)
of type proplist. In your case initial record would have been:

-record(show, {item, quantity, cost, backpack}).

Then when you would need to store source and company you could write:

#show{
  item = Item,
  quantity = Quantity,
  cost = Cost,
  backpack = [{source, Source},{company, Company}]
}