Bug 7493 [REVISED] Deleting a record with comments breaks "Recent Comments"

Bug 7493 [REVISED] Deleting a record with comments breaks "Recent Comments"

Adding foreign key constraint on biblio and borrowers:

- delete reviews when bibliographic records are deleted
- set set reviews.borrowernumber to NULL when patron records are deleted.

Before these constraints are set the database update script will
clean up existing instances of these problems by deleting reviews of
deleted biblios and setting to NULL reviews.borrowernumber for deleted
patrons.

In comments moderation, the list of comments will indicate "(deleted patron")
if the review was submitted by a patron who has since been deleted.

In the OPAC display of comments will omit the patron name altogether
if the patron has since been deleted.

To test:

1. CONFIRM THAT THE DATABASE UPDATE RUNS CORRECTLY

Before applying the patch:

 - delete the record for a title which has a review
 - delete a patron who has submitted a review (on a different title).

Viewing /cgi-bin/koha/opac-showreviews.pl should result in an error.

Apply the patch and make sure the database update runs. Viewing
the recent comments page in the OPAC should no longer result in an
error. The title with the comment from a deleted patron should
show no patron name on these pages:

 - Recent comments (opac-showreviews.pl)
 - Recent comments RSS (opac-showreviews.pl?format=rss)
 - Detail page (opac-detail.pl)

Comments from other patrons should show correctly.

2. CONFIRM THAT NEW DELETIONS PERFORM CORRECTLY

After applying the patch:

 - delete the record for a title which has a review
 - delete a patron who has submitted a review (on a different title).

Viewing /cgi-bin/koha/opac-showreviews.pl should NOT result in an error.
The review of the title which you deleted should no longer appear in the
list of recent comments.

The title with the comment from a deleted patron should
show no patron name on these pages:

 - Recent comments (opac-showreviews.pl)
 - Recent comments RSS (opac-showreviews.pl?format=rss)
 - Detail page (opac-detail.pl)

Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>