Re: Exclude constraint on ranges : commutative containment : allow only complete containment

On 1/30/20 3:46 AM, Achilleas Mantzios wrote:
> On 29/1/20 8:32 μ.μ., Adrian Klaver wrote:
>> On 1/29/20 8:12 AM, Achilleas Mantzios wrote:
>>> Hello Dear Postgresql ppl,
>>> I have a table with date ranges and need to express the following
>>> constraint : allow overlaps only if there is complete containment, e.g.
>>> allow values in rows like :
>>> [2020-01-01,2020-01-31)
>>> [2020-01-02,2020-01-10)
>>> [2020-01-10,2020-01-20)
>>>
>>> but disallow rows like
>>>
>>> [2020-01-02,2020-01-10)
>>> [2020-01-08,2020-01-11)
>>
>> I'm missing something. Can you provide a more complete example?
> Dear Adrian,
> I can give an example, lets say that we want to model the concept of
> budget, and we allow basic complete budgets covering a specific time
> period (daterange) which will have predictions and also matched actual
> transactions (Debits, Credits) , but also want "super" budgets of larger
> time periods which include a number of basic budgets (sub-budgets) and
> for which only predictions are allowed, not actual transactions. We
> could make the design strict and explicit by using referential
> constraints (basic budget pointing to a super budget) but If we chose to
> not make it strict , and conversely allow a more dynamic and liberal way
> that the system detects one form or the other , we could say :
> each sub-budget (of the lowest level of the hierarchy - although for the
> time being we have only two levels) cannot overlap with any other
> sub-budget
> each super-budget can only fully contain its sub-budgets , no partial
> overlap allowed.

Um, that makes my head hurt:) Questions:

1) Are the basic complete budgets and the sub-budgets and super budgets
existing in the same table?

2) Depending on answer to 1, to prevent overlap could you not use a form
of the example here?:

https://www.postgresql.org/docs/12/rangetypes.html#RANGETYPES-CONSTRAINT

CREATE TABLE reservation (
during tsrange,
EXCLUDE USING GIST (during WITH &&)
);

>
> This could be solved easily if there was a commutative containment
> operator like :
> CREATE OR REPLACE FUNCTION range_containment(anyrange, anyrange)
>  RETURNS boolean
>  LANGUAGE sql
>  IMMUTABLE PARALLEL SAFE STRICT
> AS $function$
> select $1 <@ $2 OR $1 @> $2;
> $function$;
>
> so range_containment returns true if the first operand is contained in
> the second or contains the second.
>
> create operator <@@> (PROCEDURE=range_containment, LEFTARG=anyrange,
> RIGHTARG=anyrange, COMMUTATOR = <@@> );
>
> But unfortunately :
>
> alter table bdynacom.acc_budget ADD CONSTRAINT acc_budget_start_end
> EXCLUDE USING gist (daterange(period_start, period_end, '[]'::text) WITH
> <@@>);
> ERROR:  operator <@@>(anyrange,anyrange) is not a member of operator
> family "range_ops"
> DETAIL:  The exclusion operator must be related to the index operator
> class for the constraint.
>
> From a small research I did this might mean recompiling the source to
> make <@@> member of range_ops .
>
>>
>>>
>>> I think that writing a new commutative range operator e.g. |<@@>
>>> which would return true if the left operand is either contained by or
>>> contains the right operand and false otherwise would solve this, I am
>>> just wondering if there is a more elegant and economical way to
>>> express this. (besides writing a trigger which is always an option).|
>>>
>>> --
>>> Achilleas Mantzios
>>> IT DEV Lead
>>> IT DEPT
>>> Dynacom Tankers Mgmt
>>>
>>
>>
>
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com