Trivial questions?

Dear Smalltalker, I'm trying to get into Smalltalk a bit more
seriously. I'm especially currently trying to get into Seaside
programmming and the persistence of Objects. I found GLASS, which seems
to be remarkabel in that aspect. Now I wonder

1) How does one do versioning in Smalltalk. AFAIU it seems, one files
out ChangeSets which then can be read in in another image. Am I wrong
about that?

2) How does one Data Migration in Smalltalk? I just know it from Rails,
where one has migrations, but how's that done in the Persistence layers
of some Smalltalk. E.g what happens if I add or remove instance
variables?

There are somewhat related question but more about GLASS. I read teh
gemstone soup up and down, and was able to install the Web Edition on my
System also. It was a few days work but I learned a lot. However I found
just a few videos about Gemstone, but not more "serious" use (with more
database related stuff, scheme changes etc) Would you mind to share
your experiences?

Regards
Friedrich

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Q-Software Solutions GmbH; Sitz: Bruchsal; Registergericht: Mannheim
Registriernummer: HRB232138; Geschaeftsfuehrer: Friedrich Dominicus

On Thu, Dec 31, 2009 at 09:29:01AM +0100, Friedrich Dominicus wrote:
> Dear Smalltalker, I'm trying to get into Smalltalk a bit more
> seriously. I'm especially currently trying to get into Seaside
> programmming and the persistence of Objects. I found GLASS, which seems
> to be remarkabel in that aspect. Now I wonder

Welcome!

> 1) How does one do versioning in Smalltalk. AFAIU it seems, one files
> out ChangeSets which then can be read in in another image. Am I wrong
> about that?

ChangeSets are a traditional way of doing this, and are still very
useful for organizing your work (in Squeak they are associated with
Projects, so you can have a Project with a ChangeSet that represents
some aspect of the system that you are working on).

Nowadays, most serious work is done with the Monticello change management
tools. You can read about Monticello here:

  http://wiki.squeak.org/squeak/1287

So it is a good idea to learn how to use ChangeSets first, but as soon
as you have done this you will want to learn how to use Monticello for
version management and sharing your code between images.

> 2) How does one Data Migration in Smalltalk? I just know it from Rails,
> where one has migrations, but how's that done in the Persistence layers
> of some Smalltalk. E.g what happens if I add or remove instance
> variables?

I don't know enough about Rails to understand the question, but in
general it is straightforward to add and remove instance variables
in Smalltalk.

> There are somewhat related question but more about GLASS. I read teh
> gemstone soup up and down, and was able to install the Web Edition on my
> System also. It was a few days work but I learned a lot. However I found
> just a few videos about Gemstone, but not more "serious" use (with more
> database related stuff, scheme changes etc) Would you mind to share
> your experiences?

Probably others on this list can give you some ideas, but I'll mention
also that there is a Gemstone mailing list that may help.

  "GemStone Smalltalk Customer Forum" <[hidden email]>
  List-Subscribe: <mailto:[hidden email]>
  List-Owner: <mailto:[hidden email]>

Dave

On 2009-12-31, at 6:58 AM, David T. Lewis wrote:

>> 2) How does one Data Migration in Smalltalk? I just know it from Rails,
>> where one has migrations, but how's that done in the Persistence layers
>> of some Smalltalk. E.g what happens if I add or remove instance
>> variables?
>
> I don't know enough about Rails to understand the question, but in
> general it is straightforward to add and remove instance variables
> in Smalltalk.

Hi Friedrich,

David didn't understand the question because data migration is generally a non-issue in Smalltalk. When you add or remove an instance variable, the instances of that class are automatically migrated for you. There's a class called ClassBuilder that handles this as part of creating the new class. It builds the new class, locates all the instances of the old class, creates equivalent instances of the new class, copies instance state to the new instances and updates all object reference to point to the new instances. Finally, the old instances are discarded and available for garbage collection.

The one area where data migration does become an issue is when objects have been serialized and stored outside an image. Then reading them back into an image requires migration. There are various methods of doing this, and they tend to depend on the particular needs of your application. Of course, if you're using Gemstone, there's not much need to store objects outside an image. :-)

Colin

On Dec 31, 2009, at 12:29 AM, Friedrich Dominicus wrote:

> Dear Smalltalker, I'm trying to get into Smalltalk a bit more
> seriously. I'm especially currently trying to get into Seaside
> programmming and the persistence of Objects. I found GLASS, which seems
> to be remarkabel in that aspect.

Welcome!

> Now I wonder
>
> 1) How does one do versioning in Smalltalk. AFAIU it seems, one files
> out ChangeSets which then can be read in in another image. Am I wrong
> about that?

As mentioned, Monticello is typically used in Squeak/Pharo/Gemstone. Other dialects (implementations) of Smalltalk have their own, proprietary approach to code versioning. In Cincom Smalltalk it is Store; in VA Smalltalk it is Envy; and in Dolphin it is Source Tracking System.

> 2) How does one Data Migration in Smalltalk? I just know it from Rails,
> where one has migrations, but how's that done in the Persistence layers
> of some Smalltalk. E.g what happens if I add or remove instance
> variables?

I discussed how GemStone handles this in a recent presentation. You can watch it by selecting the video on class versions at http://programminggems.wordpress.com/2009/12/01/smalltalks-2/.

> There are somewhat related question but more about GLASS. I read teh
> gemstone soup up and down, and was able to install the Web Edition on my
> System also. It was a few days work but I learned a lot. However I found
> just a few videos about Gemstone, but not more "serious" use (with more
> database related stuff, scheme changes etc).

GemStone's Programming Guide has an entire chapter on migrating objects. See "Class Versions and Instance Migration" in the Programming Guide found (near the bottom right) at http://seaside.gemstone.com/about.html.

> Would you mind to share your experiences?

The great thing about Smalltalk, is that objects encapsulate state and behavior, and the only access to the state is by sending a message. In a dynamic system (like Smalltalk), the sender of the message does not know the position (or even the existence) of instance variables, so the receiver can "intercept" the request and choose to handle it in its own way. Thus, if a person has a dateOfBirth but not an age instance variable, a request for an age can return the correct answer by calculating the age from the dateOfBirth.

> Regards
> Friedrich
>
> --
> Q-Software Solutions GmbH; Sitz: Bruchsal; Registergericht: Mannheim
> Registriernummer: HRB232138; Geschaeftsfuehrer: Friedrich Dominicus

Keep those questions coming!

James Foster
http://programminggems.wordpress.com/

If you're a Rails developer and you're talking about "Data Migration,"
I'd guess your talking about database management with ActiveRecord?
So, ActiveRecord (in the context of Ruby) in an implementation of a
design pattern of the same name. ActiveRecord is an ORM, so maybe you
should have a look at Glorp (which is also an ORM, but for Smalltalk.)

Also, you should give Magma a try too. I played around with it over a
weekend, and was nearly convinced that I'd rather never deal with SQL
or ORMs every again. Nearly:) Anyway, most of the time you won't need
a database until your app needs to scale past a demo, because you can
just use image based persistence when developing.

Hopefully some of that helps.

On Thu, Dec 31, 2009 at 12:29 AM, Friedrich Dominicus
<[hidden email]> wrote:


--
Ron

On Thu, Dec 31, 2009 at 09:59:17PM -0500, Stephen Pair wrote:
>

On Thu, Dec 31, 2009 at 09:59:17PM -0500, Stephen Pair wrote:
Hello Stephen,

What an odd coincidence that you should happen to reply to this thread.
It just happens that earlier today I was trying to collect various
archival versions of SystemTracer in hopes of collecting it into a
Monticello archive and bringing it up to date with the latest 64-bit
image tracing changes. I was not able to locate a copy of your
SystemTracer2.sar, which is referenced from SqueakMap:
  http://people.advantive.com/~spair/squeak/SystemTracer2.sar

If you happen to have a copy sitting around on a floppy disk or
some such thing, I'd appreciate very much if you could send it
to me (or reply to this list). Also, it seems that having things
like this be MIT licensed is considered a good thing in some circles,
so you are able to release your work as MIT licensed, please
mention that for the record.

Thanks!

Dave

Colin Putney <[hidden email]> writes:

Well that' why I asked because I found nothing about it in the videos
I've seen. So either it it "trivial" or so difficult that nobody dared
to do it ;-)

>
> The one area where data migration does become an issue is when objects
> have been serialized and stored outside an image. Then reading them
> back into an image requires migration. There are various methods of
> doing this, and they tend to depend on the particular needs of your
> application. Of course, if you're using Gemstone, there's not much
> need to store objects outside an image. :-)
I'm not yet decided, but it seems Gemstone is the most elaborate in that
area and it seems to be rock solid. I'm not that much a fan of things
which have not shown (yet) that they can handle that kind of stuff. Just
imagine, I´d decide to go on "own" way just to figure out. Well
Friedrich, you did not get it right....

Regards
Friedrich

--
Q-Software Solutions GmbH; Sitz: Bruchsal; Registergericht: Mannheim
Registriernummer: HRB232138; Geschaeftsfuehrer: Friedrich Dominicus

James Foster <[hidden email]> writes:
Ok, I see so I have to decide upon my Smalltalk of choice and/or to use
Monticelle on every of them....

>
>> 2) How does one Data Migration in Smalltalk? I just know it from Rails,
>> where one has migrations, but how's that done in the Persistence layers
>> of some Smalltalk. E.g what happens if I add or remove instance
>> variables?
>
> I discussed how GemStone handles this in a recent presentation. You
> can watch it by selecting the video on class versions at
> http://programminggems.wordpress.com/2009/12/01/smalltalks-2/.

Thanks, I'll look into it today.

Ah I have over-read it on the first round.

Thanks
Friedrich


--
Q-Software Solutions GmbH; Sitz: Bruchsal; Registergericht: Mannheim
Registriernummer: HRB232138; Geschaeftsfuehrer: Friedrich Dominicus