Glorp reconnection management (was: Re: Glorp: how to reconnect after image shutdown / load?)

[hidden email] wrote:
> Herby,
>
> I am not aware of any automatic reconnect tools. Kepping a DB connection
> alive after an image is closed is surely not desired and chances are the
> DB will close the inactive session eventually anyways.

Hm. When I though about it, image save / load cycle is just one example
of losing a connection to db. So the question is more on "how to manage
possible disconnections / reconnections"?

> So it's probably best to make the DB connections reconnect on demand.
> That means that whenever you open a session, check if a DB connection is
> available or establish a new one otherwise.

Hm, I though that once I open a session it does actually connect on
demand (it has Login, system and all the information for it). Does it
actually mean that if I want to stay connected I must do `session login`
before each `session inUnitOfWorkDo:`?

> There are many scenarios that can lead to the loss of a DB connection
> that you usually cannot influence (network connection drops, DB server
> has some error condition etc.) , so this is a good idea anyways.

As written above, I thought glorp manages this kind of reconnection
itself. If not, can someone point me to the some example where this is
managed? I am asking because in Glorp book I did not find anything about
this (I have read it).

Thanks, Herby

On Wed, Aug 02, 2017 at 11:30:27AM +0200, Herby Vojčík wrote:
> Hm, I though that once I open a session it does actually connect on
> demand (it has Login, system and all the information for it). Does
> it actually mean that if I want to stay connected I must do `session
> login` before each `session inUnitOfWorkDo:`?

No.

> As written above, I thought glorp manages this kind of reconnection
> itself. If not, can someone point me to the some example where this
> is managed? I am asking because in Glorp book I did not find
> anything about this (I have read it).

If used with Seaside, typically when a Seaside session is started, your
application's custom subclass of WASession starts a database session, be it for
Glorp, some other OODB, good olde SQL, etc. From Sven's Reddit.st:

  RedditSession>>glorpSession
    glorpSession ifNil: [ glorpSession := self newGlorpSession ].
    glorpSession accessor isLoggedIn
      ifFalse: [ glorpSession accessor login ].
    ^ glorpSession

See the senders of #glorpSession.

Also read the chapters of HPI's Seaside tutorial on tasks & sessions, and
persistence.

  http://www.hpi.uni-potsdam.de/hirschfeld/seaside/tutorial

Pierce

Pierce Ng wrote:
> On Wed, Aug 02, 2017 at 11:30:27AM +0200, Herby Vojčík wrote:
>> Hm, I though that once I open a session it does actually connect on
>> demand (it has Login, system and all the information for it). Does
>> it actually mean that if I want to stay connected I must do `session
>> login` before each `session inUnitOfWorkDo:`?
>
> No.

Great.

Yeah, I ended up with this. And planning to set it to nil on each image
loading (not sure how, yet, I don't want to register a class as a
handler, but I'll manage, I hope).

>      glorpSession accessor isLoggedIn
>        ifFalse: [ glorpSession accessor login ].

Looking at state of the art code:


DatabaseAccessor >> login
       
        | |
        self loginIfError: [:ex |
                ex pass].
        "Just to help avoid confusion if someone thinks they're getting a login
object back from this"
        ^nil.


GlorpSession >> isLoggedIn
        ^accessor isLoggedIn


GlorpSession >> login
        self isLoggedIn ifTrue: [^nil].
        ^self loginIfError: [:ex | ex pass]


GlorpSession >> loginIfError: aBlock
        | result |
        result := self accessor loginIfError: aBlock.
        system platform characterEncoding: accessor encoding.
        ^result


it seems this `... ifFalse: ...` is in fact the same thing as
`glorpSession login` (yes, it does set an encoding, but otherwise, it's
the same, isn't it)?

Doesn't this counter the previous "no", in fact? If I do all operations
via `self glorpSession doSomething`, then it actually does `glorpSession
login` before each action...

>      ^ glorpSession
>
> See the senders of #glorpSession.
>
> Also read the chapters of HPI's Seaside tutorial on tasks&  sessions, and
> persistence.
>
>    http://www.hpi.uni-potsdam.de/hirschfeld/seaside/tutorial

1. Link does not load.
2. I am doing it with ZnServer, no Seaside there.

> Pierce

Thanks, Herby

On Thu, Aug 03, 2017 at 03:27:16PM +0200, Herby Vojčík wrote:
> Looking at state of the art code:
> GlorpSession >> loginIfError: aBlock
> | result |
> result := self accessor loginIfError: aBlock.
> system platform characterEncoding: accessor encoding.
> ^result

In the line "result := self accessor loginIfError: aBlock", "self accessor" is
not an instance of DatabaseAccessor, because

  DatabaseAccessor>>loginIfError: aBlock
    self subclassResponsibility

"self accessor" is an instance of PharoDatabaseAccessor, and

  PharoDatabaseAccessor>>loginIfError: aBlock
    self log: 'Login'.
    self databaseDriver: self connectionClass new.
    self
      execute: [
        self databaseDriver connect: currentLogin.
        currentLogin secure
          ifTrue: [ currentLogin discardPassword ]
        ]
      ifError: aBlock.
    self log: 'Login finished'

  PharoDatabaseAccessor>>isLoggedIn
    self databaseDriver ifNil: [^ false].
    ^ self databaseDriver isConnected

Connecting to my instance of Reddit (actually RedditSt20 using SQLite not
PostgreSQL), adding a link and then clicking refresh, Transcript shows:

  Login
  Login finished
  SELECT t1.id, t1.url, t1.title, t1.created, t1.points
   FROM REDDIT_LINKS t1 ORDER BY t1.points DESC LIMIT 20  an OrderedCollection()
  SELECT t1.id, t1.url, t1.title, t1.created, t1.points
   FROM REDDIT_LINKS t1 ORDER BY t1.created DESC LIMIT 20  an OrderedCollection()
  Begin Transaction
  INSERT INTO REDDIT_LINKS (url,title,created,points)  VALUES (?,?,?,?)  
    an Array('http://planet.smalltalk.org' 'Planet Smalltalk' 2017-08-04T22:25:14.558667+08:00 0)
  SELECT last_insert_rowid()
  (0.0 s)
  Commit Transaction
  SELECT t1.id, t1.url, t1.title, t1.created, t1.points
   FROM REDDIT_LINKS t1 ORDER BY t1.points DESC LIMIT 20  an OrderedCollection()
  SELECT t1.id, t1.url, t1.title, t1.created, t1.points
   FROM REDDIT_LINKS t1 ORDER BY t1.created DESC LIMIT 20  an OrderedCollection()

Login happened once. Clicking "New Session":

  Logout
  Logout finished
  Login
  Login finished
  SELECT t1.id, t1.url, t1.title, t1.created, t1.points
   FROM REDDIT_LINKS t1 ORDER BY t1.points DESC LIMIT 20  an OrderedCollection()
  SELECT t1.id, t1.url, t1.title, t1.created, t1.points
   FROM REDDIT_LINKS t1 ORDER BY t1.created DESC LIMIT 20  an OrderedCollection()

Clicking "Refresh" in the application:

  SELECT t1.id, t1.url, t1.title, t1.created, t1.points
   FROM REDDIT_LINKS t1 ORDER BY t1.points DESC LIMIT 20  an OrderedCollection()
  SELECT t1.id, t1.url, t1.title, t1.created, t1.points
   FROM REDDIT_LINKS t1 ORDER BY t1.created DESC LIMIT 20  an OrderedCollection()


Pierce