Re: New versions vs. serialization

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Hi steeve

I am facing the same problem. Kindly send me sample code or workarounds for
this problem.

Thanks

"Steve Teeples" wrote:

> Fred,
> FYI... I implemented your proposed solution and it worked. I now write data
> to a dictionary and write it to disk. I then recall the dictionary, look for
> keys, and repopulate my test structures only if the key was found. It was
> trick creating a dictionary that stored any object with a cooresponding key
> but it is working. Thanks for the suggestion.
> --
> Steve
>
>
> "Fred Mellender" wrote:
>
> > Don't know if this solves your problem, but you could use one of the classes
> > that implements IDictionary interface, and is serializable. The keys would
> > be strings that represented the field named. The values would be objects
> > that you would have to cast to the correct type when you pulled them from
> > the dictionary. If a field was not found it could be added with a default
> > value (and saved when the dictionary was written out). Accessing a field
> > through a dictionary in this way is rather expensive in CPU time, though.
> >
> > If you did not want to pay the cost to access the "fields" from the
> > dictionary, each time they are needed, you could make a constructor for your
> > extensible class(es). The constructor would read the serialized dictionary
> > from the file. For each field in the class, it would attempt to fetch it
> > from the dictionary; if found it would assign it from the dictionary to the
> > field in the object. If not found, it would initialize it appropriately.
> > After construction, access to the fields is just from the object.
> >
> > When your extensible class changes, you have to recompile the new class
> > definition and change the constructor. However, the old serialized
> > dictionary will be read and the new version of the class initialized with
> > the existing fields from the dictionary. The new fields would be defaulted
> > by the new constructor code you wrote, when/if they were not found in the
> > dictionary.
> >
> > Some part of your application would write out the serializable dictionary,
> > after updating the key/values in the dictionary from the object you were
> > using.
> >
> > This is about the same as saving XML and parsing it to build an object of
> > "extensible class", but use of the dictionary saves you the trouble of
> > writing parsing logic.
> >
> > You could have separate dictionaries and files for each extensible class,
> > but it might be easier to have one serializable dictionary. You could
> > easily qualify the field names (strings) with the class, as in "foo.in",
> > "bar.in", and use them to build the "bar" and "foo" objects appropriately.
> >
> >
> >
> > "Steve Teeples" <SteveTeeples@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
> > news:5536BC7F-2DB5-452A-B4CF-3009FB7F651A@xxxxxxxxxxxxxxxx
> > > Did you ever find a solution to this problem? I have a similar issue and
> > > am
> > > looking for a solution.
> > > --
> > > Steve
> > >
> > >
> > > "Jesper" wrote:
> > >
> > >> Hi,
> > >>
> > >> I'm writing a program which is, and will continue to be, constantly
> > >> extended
> > >> with functionality that require information. Until now the source of this
> > >> information has been found and modified using notepad in a txt file that
> > >> was
> > >> parsed into fields in objects. (This solution because this was the format
> > >> that an older fortran program was using and we needed to do it in this
> > >> way in
> > >> a transition period). Now I would like be able to save from the program
> > >> and
> > >> wish to switch to object serialization, but I'm concerned about backward
> > >> compatibility if my classes that are serialized on disk is constantly
> > >> extended.
> > >>
> > >> If I extend a class with a field and try to desirialize this class from a
> > >> source which did not have the field, I guess I'll get an exception,
> > >> Right?.
> > >> Are there any attributes that can provide some kind of default values for
> > >> fields or indicate that it is 'OK!' that the field wasn't found.
> > >>
> > >> Must a class match exactly the fields.
> > >>
> > >> Alternatively I would use xml and write my own serialization and
> > >> deserialization methods. Rather cumbersome but maybe necessary if I want
> > >> this
> > >> degree of freedom.
> > >>
> > >> Another way could be to keep the old framework and then parse information
> > >> from this old framework to the new one - like when you open a word 97
> > >> document in word 2003.
> > >>
> > >> Please comment.
> > >>
> > >> best regards Jesper, Denmark.
> > >>
> >
> >
> >
.

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