Re: Is there a way to address all elements of JSON array when creating a constraint in PosgreSQL?

On Tue, Jan 21, 2014 at 1:34 AM, Maciej Szopinski <maciej(dot)sz(at)gmail(dot)com>wrote:

> Hello,
>
> Does PostgreSQL provide any notation/method for putting a constraint on
> each element of a JSON array?
>
> An example to illustrate:
>
>
> [...]

> I know that this can be done by extracting products to a separate table
> with a foreign key to orders. But I want to know if this is possible within
> single JSON column, so I can keep that in mind when designing a database
> schema.
>
>
If you write a short function to help, it's possible. You would need a
subquery to make this assertion, but you can't add one directly as a check
constraint:

create table orders (data JSON);

alter table orders add check (1 <= ALL((select
array_agg((a->>'product_id')::integer) from
json_array_elements(data->'products') as a)));
ERROR: cannot use subquery in check constraint

create function data_product_ids(JSON) returns integer[] immutable as $$
select array_agg((a->>'product_id')::integer) from
json_array_elements($1->'products') as a $$ language sql ;
CREATE FUNCTION

alter table orders add check (1 <= ALL(data_product_ids(data)));
ALTER TABLE

insert into orders (data) values ('{"products": [{ "product_id":1 }, {
"product_id":2 }]}');
INSERT 0 1

insert into orders (data) values ('{"products": [{ "product_id":0 }, {
"product_id":2 }]}');
ERROR: new row for relation "orders" violates check constraint
"orders_data_check"
DETAIL: Failing row contains ({"products": [{ "product_id":0 }, {
"product_id":2 }]}).