Is there a way to address all elements of JSON array when creating a constraint in PosgreSQL?
Hello,
Does PostgreSQL provide any notation/method for putting a constraint on
each element of a JSON array?
An example to illustrate:
create table orders(data json);
insert into orders values ('
{
"order_id": 45,
"products": [
{
"product_id": 1,
"name": "Book"
},
{
"product_id": 2,
"name": "Painting"
}
]
}
');
I can easily add a constraint on the order_id field:
alter table orders add check ((data->>'order_id')::integer >= 1);
Now I need to do the same with product_id. I can put constraint on
idividual array items:
alter table orders add check ((data->'products'->0->>'product_id')::integer
= 1);
alter table orders add check ((data->'products'->1->>'product_id')::integer
= 1);
-- etc.
So what I'm looking for is some kind of wildcard operator for matching any
JSON array element:
alter table orders add check ((data->'products'->*->>'product_id')::integer
= 1);
-- ^ like this
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.
On Tue, Jan 21, 2014 at 1:34 AM, Maciej Szopinski <maciej.sz@gmail.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 }]}).