Rails - Jun 2012 - Want to make existing column unique in multiple tables

Hi,

I want to make a particular existing column unique. I have to same name
column in 4 tables. I have created a new migration but not sure what to
write inside

*def up*
*     ...........*
*     ...........*
*end
*


I am using rails 3.2.1. Please help.

-- 
Regards
Ritesh Ranjan
iPhone Developer & Designer
tapisfun.com
Follow me @ Twitter  <http://twitter.com/#!/tapisfun>

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On 26 June 2012 19:48, ritesh ranjan
<riteshr.designs-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Hi,
>
> I want to make a particular existing column unique. I have to same name
> column in 4 tables. I have created a new migration but not sure what to
> write inside
It is not clear to me exactly what you want to do.  Please explain in
more detail.
>
> def up
>      ...........
>      ...........
> end
>
>
> I am using rails 3.2.1. Please help.
>
> --
> Regards
> Ritesh Ranjan
> iPhone Developer & Designer
> tapisfun.com
> Follow me @ Twitter
>
> --
> You received this message because you are subscribed to the Google Groups
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There is no super quick way to do that.
Are you looking to do it just for your migration, or to keep this behavior 
in the future.

What I would do is use a fifth table that contains the next value for the 
incremental counter.
Every time you need one or several IDs, you do use a stored proc to get the 
next value.
What''s important when doing that is thinking about concurrency.

so you would have a code that in transact sql would look like

proc getNextId(@numberOfIds int)
  declare @returnId int
  update next_id
  set @returnId = nextId
     , nextId = nextId + @numberOfIds

  return @returnId
go

Something like that normally ensure that the table is updated *at the same 
time* the value is returned to you (i.e. operation is atomic).

I guess you can do something like that on the application server layer too, 
but then you do need to continue to think about multithreading, server 
restart and things like that that can get tricky.

But to conclude on this point, having such a need normally means that your 
datamodel is not clean. If those table share a key that needs to be unique 
across tables, it means most likely that this key has the same semantic for 
all 4 tables. Therefore it should most likely be just one table (maybe with 
some extensions tables filled depending on the row, but still all should 
start with a single table).

On Tuesday, June 26, 2012 8:48:23 PM UTC+2, ritesh ranjan
wrote:
>
> Hi,
>
> I want to make a particular existing column unique. I have to same name 
> column in 4 tables. I have created a new migration but not sure what to 
> write inside 
>
> *def up*
> *     ...........*
> *     ...........*
> *end
> *
>
>
> I am using rails 3.2.1. Please help.
>
> -- 
> Regards
> Ritesh Ranjan
> iPhone Developer & Designer
> tapisfun.com
> Follow me @ Twitter  <http://twitter.com/#!/tapisfun>
>
>  
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