I just found out that this is a feature introduced in PostgreSQL 10,
back in 2017.
Besides this being the standard way to define an “auto incremental
column” introduced in SQL:2003[0], called “identity columns”, in
PostgreSQL the new syntax has the following pros, according to [1]:
* No need to explicitly grant usage on the generated sequence.
* Can restart the sequence with only the name of the table and column;
no need to know the sequence’s name.
* An identity column has no default, and the sequence is better
“linked” to the table, therefore you can not drop the default value
but leave the sequence around, and, conversely, can not drop the
sequence if the column is still defined.
Due to this, PostgreSQL’s authors recommendation is to use identity
columns instead of serial, unless there is the need for compatibility
with PostgreSQL older than 10[2], which is not our case.
According to PostgreSQL’s documentation[3], the identity column can be
‘GENERATED BY DEFAULT’ or ‘GENERATED ALWAYS’. In the latter case, it is
not possible to give a user-specified value when inserting unless
specifying ‘OVERRIDING SYSTEM VALUE’. I think this would make harder to
write pgTAP tests, and the old behaviour of serial, which is equivalent
to ‘GENERATED BY DEFAULT’, did not bring me any trouble so far.
[0]: https://sigmodrecord.org/publications/sigmodRecord/0403/E.JimAndrew-standard.pdf
[1]: https://www.2ndquadrant.com/en/blog/postgresql-10-identity-columns/
[2]: https://wiki.postgresql.org/wiki/Don't_Do_This#Don.27t_use_serial
[3]: https://www.postgresql.org/docs/15/sql-createtable.html
I intend to use the same SVG file for customers and employees, so i had
to change Oriol’s design to add a class to layers that are supposed to
be only for customers, like trees. These are hidden in the admin area.
I understood that customers and employees have to click on a campsite to
select it, and then they can book or whatever they need to do to them.
Since customers and employees most certainly will need to have different
listeners on campsites, i decided to add the link with JavaScript. To
do so, i need a custom XML attribute with the campsite’s identifier.
Since i have seen that all campsites have a label, i changed the
“identifier” to the unique combination (company_id, label). The
company_id is there because different companies could have the same
label; i left the campsite_id primary key for foreign constraints.
In this case, as a test, i add an <a> element to the campsite with a
link to edit it; we’ll discuss with Oriol what exactly it needs to do.
However, the original design had the labels in a different layer, that
interfered with the link, as the numbers must be above the path and
the link must wrap the path in order to “inherit” its shape. I had no
other recourse than to move the labels in the same layer as the paths’.
It made no sense to have a file upload in each form that needs a media,
because to reuse an existing media users would need to upload the exact
same file again; this is very unusual and unfriendly.
A better option is to have a “centralized” media section, where people
can upload files there, and then have a picker to select from there.
Ideally, there would be an upload option in the picker, but i did not
add it yet.
I’ve split the content from the media because i want users to have the
option to update a media, for instance when they need to upload a
reduced or cropped version of the same photo, without an edit they would
need to upload the file as a new media and then update all places where
the old version was used. And i did not want to trouble people that
uploads the same photo twice: without the separate relation, doing so
would throw a constraint error.
I do not believe there is any security problem to have all companies
link their media to the same file, as they were already readable by
everyone and could upload the data from a different company to their
own; in other words, it is not worse than it was now.
This is the image that is shown at the home page, and maybe other pages
in the future. We can not use a static file because this image can be
changed by the customer, not us; just like name and description.
I decided to keep the actual media content in the database, but to copy
this file out to the file system the first time it is accessed. This is
because we are going to replicate the database to a public instance that
must show exactly the same image, but the customer will update the image
from the private instance, behind a firewall. We could also synchronize
the folder where they upload the images, the same way we will replicate,
but i thought that i would make the whole thing a little more brittle:
this way if it can replicate the update of the media, it is impossible
to not have its contents; dumping it to a file is to improve subsequent
requests to the same media.
I use the hex representation of the media’s hash as the URL to the
resource, because PostgreSQL’s base64 is not URL save (i.e., it uses
RFC2045’s charset that includes the forward slash[0]), and i did not
feel necessary write a new function just to slightly reduce the URLs’
length.
Before checking if the file exists, i make sure that the given hash is
an hex string, like i do for UUID, otherwise any other check is going
to fail for sure. I moved out hex.Valid function from UUID to check for
valid hex values, but the actual hash check is inside app/media because
i doubt it will be used outside that module.
[0]: https://datatracker.ietf.org/doc/html/rfc2045#section-6.8
For now, there is only the label, type, and active fields. We will need
some field to hold the area on the map, but this requires #4, and
possibly #6, to be finished.
Part of #27.
jordi fita mas