Hi,
An idea just dawned on me.
Constraints can be commented:
COMMENT ON CONSTRAINT CONSTRAINT_NAME IS 'Here is the reason why this
constraint is guarded';
This comment (if it exists) could be used in the exception message
making the error reporting much more user friendly.
Currently the exception message is
Check constraint violation: "CONSTRAINT_NAME: <SQL OF THE CONSTRAINT>
What I am proposing would be
Check constraint violation: "CONSTRAINT_NAME: <CONSTRAINT COMMENT>
And in case there is no comment the sql could be used.
What do you think?
- rami
On 08/31/2011 07:20 PM, Rami Ojares wrote:
Hi,
I always thought that H2 does not support database wide constraints
except through triggers.
(namely constraints that can depend on the state of the whole database).
But I just realized that it does.
So I thought that this could be brought out more in the documentation
because I think it is A BIG FEATURE!
Here I have a simple example to verify db constraints.
CREATE TABLE A (ID INT PRIMARY KEY);
CREATE TABLE B (AID INT REFERENCES A);
CREATE TABLE C (
AID INT REFERENCES A,
CONSTRAINT DB_CONSTRAINT CHECK(
EXISTS(
SELECT *
FROM A
JOIN B
ON C.AID = A.ID AND A.ID = B.AID
)
)
);
INSERT INTO A VALUES(1);
INSERT INTO C VALUES(1);
INSERT INTO B VALUES(1);
INSERT INTO C VALUES(1);
The second insert will throw a constraint violation like it should.
Sweet.
- rami
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