Is there any way to tell if a database row has constraints?

Question

I'm using Perl DBI with PostgreSQL, and my users will be deleting rows from a table, some of which can't be deleted because of foreign key constraints, which is fine, but I want a way to mark those rows on the front end so that it's known which rows have constraints before trying to delete them. Right now, a user would just hit "delete" and would either get an error or have the row deleted.

Answer 1

So I figured it out on my own. For anyone in a similar situation, you can turn on transactions

$dbh->{AutoCommit} = 0;

And then try to delete the row, like this for example…

my $sth = $dbh->prepare("DELETE FROM auth_users WHERE username = ?");
$sth->execute($username);

And then check for an error...

if ( $sth->err ) { print "CAN'T be deleted.";}
else { print "CAN be deleted.";}

And then just roll back to not commit to the delete in case it could be deleted…

$dbh->rollback;

This is what works for me. If anyone has any better ideas, or some concerns with this method, feel free to share.

Answer 2

I'm not terribly familiar with PostgreSQL, but I believe you can use:

SELECT * 
FROM information_schema.table_constraints 
WHERE table_name = 'YourTable'

Update- Looks like a solid answer here: Postgres: SQL to list table foreign keys