Document connection-creation process

[Christophe Pettus]

Currently, the actual database connection is created on-demand when a cursor is requested. This is great for standard use, but there are occasional uses where it would be handy to have the connection open before requesting a cursor (for example, if you are doing a raw SQL query using the cursor(cursor_factory=) syntax.

The proposal here is to move the connection-creation mechanism to a separate public method that both the internal cursor-creation mechanism and a client of the connection object could call.

[Russell Keith-Magee]

Absent of any code, it seems like a reasonable proposal.

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Anssi Kääriäinen]

There is connection.connect() and connection.ensure_connection() methods. I don't see a reason why these couldn't be documented (that is, they seem stable enough). Documenting these (or one of these) seems like somewhat easy documentation patch.

[Aymeric Augustin]

Anssi, we've made lots of changes in the 1.6 release cycle, and I'm not sure this is the end of the story.

The internal APIs for connection establishement still look messy to me. Just obtaining a cursor involves ten methods or so!

[Anssi Kääriäinen]

I agree there is more work to do. There is no need to document everything, just ensure_connection() and connect(). Actually, even .connect() isn't necessary for this ticket. Keeping connection.ensure_connection() stable doesn't seem too bad to me.

Alternative is to document that you can do cursor = connection.cursor(); cursor.close() to ensure a connection exists. But calling methods for their side-effects is a bit ugly.

[Carlton Gibson]

#32589 was a duplicate ref documenting the need for calling close_old_connections in long-running management commands.

Ostensibly this ticket here is about connection creation, but (a decade later) a general overview of the connection life-cycle would be a nice improvement.

[dcontador]

Whoever takes this should remember to document close_old_connections (https://code.djangoproject.com/ticket/32589).