Database strong structure change: migrations

[Martin]

Hi there,

I have some major structure change issues with an ruby on rails application, and I'd like to ask you about how i can handle that.  I will make some dummy problems for you to show what i want to reach:

1. Having a Client model with first_name and last_name should now come together as name:
For the model it would be easy to have just

def name
   first_name + ' ' + last_name
end

That works, but now I want to change the database this way, so we dont need the first_name and last_name anymore:

I could create a migration having a name:string:index field.
but after that - how can I make all the first_name and last_name applied there, and remove the first_name and last_name fields?

2. same for appointments:
We had a start_datetime and an end_datetime which until now was enaugh.  but now we want to change it to
planned_start_time end actual_start_time (same for end time)

on the migration all the old data from start_datetime should be put into both (for historical data) planned end actual times.  For the future this will differ.

How can I make this migrations?

If I know about that later there will be some table changes, but maybe I understand the routines for that.
Is there also any sql way doing it with rails?  For sql itself it would be easy with INSERT..SELECT, so maybe I could generate migrations with sql code?

thanks,
Martin

[Martin]

Finaly the docs have it, so this is obsolete.

[Robert Walker]

Martin wrote in post #1143301:

> Hi there,
>
> I have some major structure change issues with an ruby on rails
> application, and I'd like to ask you about how i can handle that. I
> will
> make some dummy problems for you to show what i want to reach:
>
> 1. Having a Client model with first_name and last_name should now come
> together as name:
> For the model it would be easy to have just
>
> def name
> first_name + ' ' + last_name
> end
>
> That works, but now I want to change the database this way, so we dont
> need
> the first_name and last_name anymore:

IMHO that is a bad idea. Chances are likely that you would come to
regret that decision. If you ever use either first_name or last_name
separately from each other then you violate First Normal Form (1NF). The
bigger issue is that once you decide to concatenate these two values in
to a single field there's no going back. There is no reliable algorithm
that can separate the two distinct values.

I say if you already have separate first and last names keep it that way
and add full_name method to the model. That costs you nothing really and
preserves flexibility in your app.

> I could create a migration having a name:string:index field.
> but after that - how can I make all the first_name and last_name applied
> there, and remove the first_name and last_name fields?

Whatever you decide, you are not limited to the ActiveRecord helpers in
your migrations. You can run any arbitrary SQL you want using the
execute method:

http://guides.rubyonrails.org/migrations.html#when-helpers-aren-t-enough

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