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Message from discussion How to create a UNIQUE table constraint with migrations.
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Philip Hallstrom  
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 More options Mar 3 2010, 12:55 pm
From: Philip Hallstrom <phi...@pjkh.com>
Date: Wed, 3 Mar 2010 09:55:29 -0800
Local: Wed, Mar 3 2010 12:55 pm
Subject: Re: [Rails] How to create a UNIQUE table constraint with migrations.
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>>>>> Hi.

>>>>> This must be the most obvious thing to do, but I just can't seem  
>>>>> to
>>>>> find examples of how to do this. I would like to create a table
>>>>> with a
>>>>> table unique constraint on database level.

>>>>> In deed some migration code that would generate the following SQL

>>>>> CREATE TABLE properties (
>>>>> namespace CHAR(50),
>>>>> name      CHAR(50),
>>>>> value     VARCHAR(100),
>>>>> CONSTRAINT my_constraint UNIQUE (namespace, name)
>>>>> );

>>>> create_table :properties.....
>>>>  .....
>>>> end

>>>> add_index :properties, [:namespace, :name], :unique => true

>>> After trying this and opening my interactive SQL prompt (psql), I  
>>> can
>>> see that this only creates an index on the table not a table
>>> constraint. I can still put duplicate rows in the table.

>> Hrm.  I can't...  Rails 2.3.5, Postgresql 8.4.1 (on mac, but doubt
>> that matters)

> I am so sorry. I did't do exactly as you said, explanation:
> I used

> create_table :properties do |t|
>  .....
>  t.index [:namespace, :name], :unique => true
> end

> That does NOT create an index!!! and therefore neither a constraint!!!

> I gues that is a bug in the PostgreSQL adapter.

> But when I do as you describe using add_index syntax instead it will
> create an index (AND constraint!)

> But the fact that 't.index [:namespace, :name], :unique => true' does
> not generate an index is a bug, right?

> Thanks for all help. I appreciate the time you've spent on this.

That does indeed look like a bug.  I just tried it and it doesn't  
work.  What's strange is the source code seems to say that "t.index"  
simply calls "add_index" just like if I'd done it normally.

I just tried it using MySQL as the backend and it does NOT work either.

+------------+--------------+------+-----+---------+----------------+
| Field      | Type         | Null | Key | Default | Extra          |
+------------+--------------+------+-----+---------+----------------+
| id         | int(11)      | NO   | PRI | NULL    | auto_increment |
| a          | varchar(255) | YES  |     | NULL    |                |
| b          | varchar(255) | YES  |     | NULL    |                |
| created_at | datetime     | YES  |     | NULL    |                |
| updated_at | datetime     | YES  |     | NULL    |                |
+------------+--------------+------+-----+---------+----------------+

So, at least it's not a postgresql specific bug.

You should submit a ticket to the Rails folks...

-philip


 
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