using constraint based paritioning to fix EAV type schemas? (view inheritance and constraints)

On 7/18/06, Aaron Bono <postgresql@aranya.com> wrote:

On 18 Jul 2006 09:07:08 -0700, Andrew Hammond <
andrew.george.hammond@gmail.com> wrote:

I have a client with the following EAV inspired schema.

CREATE TABLE many_tables (
table_id text primary key, -- defines which virtual table is
encoded
attribute1 text,
attribute2 text,
attribute3 text,
attribute4 text,
...
);

I'd like to use a mix of constraint based paritioning, rules
_and_views_ to implement a real schema underneath this mess, like the
following.

CREATE TABLE cat (
cat_id INTEGER PRIMARY KEY,
cat_name TEXT NOT NULL,
aloofness NUMERIC(1,3) DEFAULT 1.0 CHECK (0.0 <= aloofness AND
aloofness <= 1.0)
);

CREATE RULE many_tables_cat_insert AS
ON INSERT TO many_tables WHERE table_id = 'cat' DO INSTEAD
INSERT INTO cat (cat_id, cat_name, aloofness) VALUES (
CAST(attribute1 AS integer),
attribute2,
CAST(attribute3 AS numeric(1,3))
-- gleefully ignore the other attributes
);

-- etc for UPDATE, and DELETE rules

-- This part doesn't work
CREATE VIEW many_tables_a (CHECK (table_id = 'cat')) INHERITS
(many_tables) AS
SELECT 'cat' AS table_id,
CAST(cat_id AS text) AS attribute1,
cat_name AS attribute2,
CAST(aloofness AS text) AS attribute3,
null AS attribute4, ...
FROM cat;

So, I guess I'm stuck doing the UNION ALL approach in this instance.
This won't get me the partitioning win, nor the flexibility and
cleanliness of design that I'd get with inheritance.

As far as I can see, supporting the above would it mean adding
inheritance and constraint support to views. Does anyone have a better
approach?

If you don't mind having redundant data, you could change the ON INSERT
trigger to copy the data into cat, add an ON UPDATE trigger (you should do
this anyway) and revoke direct insert/update to cat. Then you don't need
many_tables_a or a UNION.

There's already a performance problem, I suspect that would just exacerbate
it. Since I want to encourage developers to use the relational tables
instead of the many_tables table, refusing DML wouldn't be a good idea.

Of course I don't know if this achieves your intended result or not. What

is your business requirement for this?

The current virtual table design has performance (as well as maitenance)
issues. Performance tuning is problematic. A major re-design of the
application is not something that can be done until the next major release.
However, if I can slide a proper relational schema underneath this
hodge-podge table while retaining compatability for legacy apps then it
becomes possible to fix parts of the application to use the relational
tables incrementally on an as-needed basis.

If I could get constraint based exclusioning to work with the partitioning,
then I would be able to realize performance improvements immediately (which
is always good for a consultant). Unfortunately I don't see any way to do
this. Inheritance seems to fit backwards from what I'm actually trying to
do.

I've seen a few EAV designs in practice. They've all been problematic. I'd
like to have a better way of dealing with them. Which is why I'm tentatively
suggesting support for inheritance and constraints in views. If there's some
other way to achieve constraint based exclusion across a UNION of
heterogenous tables, I'd love to hear it.

Drew

Ühel kenal päeval, T, 2006-07-18 kell 16:44, kirjutas Andrew Hammond:

On 7/18/06, Aaron Bono <postgresql@aranya.com> wrote:
On 18 Jul 2006 09:07:08 -0700, Andrew Hammond
<andrew.george.hammond@gmail.com> wrote:

I have a client with the following EAV inspired
schema.

CREATE TABLE many_tables (
table_id text primary key, -- defines which
virtual table is
encoded
attribute1 text,
attribute2 text,
attribute3 text,
attribute4 text,
...
);

Maybe you can approach the problem from another end, and make the
many_tables table the virtual one and all the others into real tables ?

--
----------------
Hannu Krosing
Database Architect
Skype Technologies OÜ
Akadeemia tee 21 F, Tallinn, 12618, Estonia

Skype me: callto:hkrosing
Get Skype for free: http://www.skype.com

Hannu Krosing wrote:

Ühel kenal päeval, T, 2006-07-18 kell 16:44, kirjutas Andrew Hammond:

On 7/18/06, Aaron Bono <postgresql@aranya.com> wrote:
On 18 Jul 2006 09:07:08 -0700, Andrew Hammond
<andrew.george.hammond@gmail.com> wrote:

I have a client with the following EAV inspired
schema.

CREATE TABLE many_tables (
table_id text primary key, -- defines which
virtual table is
encoded
attribute1 text,
attribute2 text,
attribute3 text,
attribute4 text,
...
);

Maybe you can approach the problem from another end, and make the
many_tables table the virtual one and all the others into real tables ?

The many_tables table already exists. It works about as poorly as you'd
expect. My goal is to migrate away from this attrocious design. My
question is how best to do that. I'd like to take advantage of table
partitioning and constraint based exclusion, but I can't figure out how
to do it since the underlying tables are heterogenous in nature.

Perhaps I'm going about this the wrong way though. I think I'll
partition based on table_id and leave the native storage in the crappy
text fields. Then create views of what should be the real, relational
tables. That lets the developers migrate and (I hope) eases the
performance burden somewhat. Once the code migration is complete I can
finalize the data move.

Ühel kenal päeval, K, 2006-07-19 kell 00:20, kirjutas Hannu Krosing:

Ühel kenal päeval, T, 2006-07-18 kell 16:44, kirjutas Andrew Hammond:

On 7/18/06, Aaron Bono <postgresql@aranya.com> wrote:
On 18 Jul 2006 09:07:08 -0700, Andrew Hammond
<andrew.george.hammond@gmail.com> wrote:

I have a client with the following EAV inspired
schema.

CREATE TABLE many_tables (
table_id text primary key, -- defines which
virtual table is
encoded
attribute1 text,
attribute2 text,
attribute3 text,
attribute4 text,
...
);

Maybe you can approach the problem from another end, and make the
many_tables table the virtual one and all the others into real tables ?

Oops, I see you kind of are :)

Maybe you can solve some of the problems doing a VIEW over pl/SQL
function ?

And/or maybe using triggers instead of rules.

--
----------------
Hannu Krosing
Database Architect
Skype Technologies OÜ
Akadeemia tee 21 F, Tallinn, 12618, Estonia

Skype me: callto:hkrosing
Get Skype for free: http://www.skype.com

I've seen a few EAV designs in practice. They've all been
problematic. I'd like to have a better way of dealing with
them. Which is why I'm tentatively suggesting support for
inheritance and constraints in views. If there's some other
way to achieve constraint based exclusion across a UNION of
heterogenous tables, I'd love to hear it.

If you do your own rules anyway, why can't you use inheritance and
create the rules
on the parent table and the constraints on the child tables ?

You can still use the child tables directly if you want.

Andreas

I've seen a few EAV designs in practice. They've all been

problematic.

I'd like to have a better way of dealing with them. Which is why I'm

tentatively suggesting support for inheritance and constraints in
views. If there's some other way to achieve constraint based

exclusion

across a UNION of heterogenous tables, I'd love to hear it.

If you do your own rules anyway, why can't you use
inheritance and create the rules on the parent table and the
constraints on the child tables ?

Ah, sorry, just saw that you want different column names in your
subtables.

Add me as another vote to extend the new constraint elimination to union
all views :-)

Andreas