Hi,
You can do this today using inheritance.
define a table "tagable" with person & blog as child tables.
than you could run queries like:
select * from tags JOIN tagable on (tag_id = tag_fk);
tag_id | tag_desc | id | tag_fk | data
--------+--------------+----+--------+------------------------
3 | blog tag 1 | 1 | 3 | blog tagged by tag 1
2 | person tag 2 | 2 | 2 | person tagged by tag 2
simple :)
Regards,
- Jony
On Fri, Aug 14, 2015 at 4:04 AM, Adrian Klaver <adrian.klaver@xxxxxxxxxxx> wrote:
On 08/13/2015 05:59 PM, Guyren Howe wrote:
Ccing list
On Aug 13, 2015, at 17:49 , Adrian Klaver <adrian.klaver@xxxxxxxxxxx> wrote:
A polymorphic join is where a fk contains not just an id but an indicator of which table it refers to.
I am pretty sure it already does that:
http://www.postgresql.org/docs/9.4/interactive/sql-createtable.html
REFERENCES reftable [ ( refcolumn ) ]
I apologize for not being clearer.
The point is that the fk in different rows can reference different tables. I might want to be able to attach a tag to a person or a blog post, say. And then I want to find all the persons and blog posts with a particular tag, in a single query.
Could you just not turn that around?:
tag
tag_id
tag_desc
person
person_id
tag_fk references tag
blog
blog_id
tag_fk references tag
The simplest implementation is to have a table reference as a first-class value I can store in a field.
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
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