Обсуждение: Add custom properties to a column's definition (pg_attribute)

On 09/01/2014 20:08, Brooke Beacham wrote:
> Can anyone suggest a way to associate a set of custom properties
> (key/value pairs) with a column's definition (ie pg_attribute)?
>
> (without having to replicate/maintain a table of columns separately from
> the system catalog)
>
> For example:
> * I have a table with 50 columns
> * I'd like to 'flag' 30 of those columns as group - 'A' and the other 20
> as group - 'B'
>
>
> So I'd like a way to add custom metdata (k/v pairs) to a column's
> definition (not the actual rows of data).

You could use the comment facility -

   COMMENT ON COLUMN tablename.columnname IS IS '....';

- to store some JSON or the like, though you'll have to parse it
client-side.

Ray.


--
Raymond O'Donnell :: Galway :: Ireland
rod@iol.ie

On 09/01/2014 20:16, Raymond O'Donnell wrote:
> On 09/01/2014 20:08, Brooke Beacham wrote:
>> Can anyone suggest a way to associate a set of custom properties
>> (key/value pairs) with a column's definition (ie pg_attribute)?
>>
>> (without having to replicate/maintain a table of columns separately from
>> the system catalog)
>>
>> For example:
>> * I have a table with 50 columns
>> * I'd like to 'flag' 30 of those columns as group - 'A' and the other 20
>> as group - 'B'
>>
>>
>> So I'd like a way to add custom metdata (k/v pairs) to a column's
>> definition (not the actual rows of data).
>
> You could use the comment facility -
>
>    COMMENT ON COLUMN tablename.columnname IS IS '....';

Whoops, sorry, an extra "is" got in there.... should have been:

   COMMENT ON COLUMN tablename.columnname IS '....';

Ray.



--
Raymond O'Donnell :: Galway :: Ireland
rod@iol.ie

Brooke Beacham wrote
> (without having to replicate/maintain a table of columns separately from
> the system catalog)

Just create the friggin' table and wrap whatever logic you want in a view
(or functions) so that you at least get usable results/defaults for any
columns you haven't added.

Any solution you pick has the risk of becoming out-of-sync so tossing out
the best solution does more harm than good.

In terms of "group" columns you might just consider creating two tables that
have a one-to-one relationship to each other (or three, the base table and
then group A and group B tables).

A lot depends on the why and structure of your model but there is no
standard facility for custom column meta-data and though the comment
facility can be used for this I much prefer to leave that for human
consumption and have something more structured and easily customize-able for
meta-data.

David J.




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