<p>In <a href="https://github.com/dbsrgits/dbix-class/pull/88#discussion_r43756701">lib/DBIx/Class/ResultSource.pm</a>:</p>
<pre style='color:#555'>> +=item Return Value: Hashref of unique constraint data
> +
> +=back
> +
> + my $unique_info = $source->unique_constraints_info();
> +
> +Read-only accessor returning all information about unique constraints.
> +
> +The hashref is keyed by the constraint name, and the values are
> +hashrefs contaning two keys:
> +
> +C<columns> is an arrayref of the columns originally provided to
> +L</add_unique_constraint> or L</add_unique_constraints>;
> +
> +C<extra> is the hashref originally passed to
> +L</add_unique_constraint>, or an empty hashref if none was provided.
</pre>
<p>Do not do <code>an empty hashref if none was provided</code>. Either the user supplied one or they did not, do not add anything on your own.</p>
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