Jarl Friis wrote:
> Philip Hallstrom <[email protected]> writes:
>
>>> CREATE TABLE properties (
>>
>> 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.
Excerpt from the PostgreSQL manual:
----------------------------------
PostgreSQL automatically creates a unique index when a unique constraint
or a primary key is defined for a table. The index covers the columns
that make up the primary key or unique columns (a multicolumn index, if
appropriate), and is the mechanism that enforces the constraint.
----------------------------------
>From what I gather using "add_index :properties, [:namespace, :name],
:unique => true" should do pretty much the same thing as adding a unique
constraint, and do so in a database agnostic manner.
If you really want to use the constraint then simply execute the SQL
yourself:
Example:
CREATE TABLE properties (
namespace CHAR(50),
name CHAR(50),
value VARCHAR(100),
);
execute <<-SQL
ALTER TABLE products
ADD CONSTRAINT my_constraint UNIQUE (namespace, name)
SQL
Note: Don't forget to drop the constraint in your down method if
necessary.
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