[Tutor] associating two objects without ORM and processing a text file

[Dave Angel]

On 02/11/2013 12:14 AM, neubyr wrote:
> I have a text file with each line in following format:
>
> Book Name, Author Name, Genre, Publication Date
>
> I would like to perform following queries on this file:
>   * Get all books written by an author
>   * Remove all books of an author
>   * Get information about a book (pretty print matching line!)
>   * Get books of particular genre
>
> Also, I would like to add and delete entries in this file. I am not
> planning to use any database for this purpose and would like to get better
> grasp on file parsing and classes/OOP.

I take it from this that this is a class assignment, and that neither 
speed nor enormous data capacity nor concurrent operation is a 
requirement.  But your professor may have other requirements that you 
haven't told us about.

I need some help in creating classes
> and following are my initial thoughts:
>
> # Create a class for Book object
> class Book:
>    atributes: name, author_name, genre, publication-date
>
> # Create
> Author:
>   attribute(s): name

Is this in order to save space, since each Book instance can then have a 
reference to an Author object, rather than a reference to a string 
containing the Author's name.

If you deem this class useful, then don't you also want one for Genre ?


>
> # Create class for reading and writing to the file
> class Booksfile:
>    methods: ??

Why ?  Are you transliterating this from Java ?

>
>
> * How do I associate/relate Book and Author classes so that it will help me
> in getting information like 'get list of books written by an author'? Data
> attribute?

If performance doesn't matter, then create one list of Book instances, 
and search it for whichever characteristics you like.


> * Should I create a new Booksfile object for reading, writing and deleting
> entries in the file OR add corresponding methods to the book object itself?

Neither, a pair of regular functions will do fine.  One that loads when 
you start the program, and another that saves the file when you exit. 
If you really expect to update the file incrementally, deleting entries 
in it, then think hard about your decision to roll your own database.  A 
text file isn't random access.

>
> I am not planning to use SQLite or any database and would like to use text
> file only. Appreciate any help on designing such application.
>
>

The real question is where you might proceed after meeting these first 
requirements.  For example, if you expect the list to grow to a few 
hundred million entries, then you'll need to be very careful about 
layout.  And starting and exiting the program would be very slow, since 
you can do nothing till all the data has been loaded in and converted to 
objects.

Or perhaps you'll want to have another file with additional author data, 
associated with the first by carefully spelling the author's name the 
same in all cases.  In that case, having a separate Author class makes 
great sense.  So if you expect to grow in that direction, then you 
should create the class now, even though it has only one attribute.


-- 
DaveA