Django Tutorial Part 3 - UML

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1

Hi,
Can someone please explain why the “1” in the upper right is not “1…*”?

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It’s from here: Django Tutorial Part 3: Using models - Learn web development | MDN
Thanks,

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Hello @Rafael_Green

i will answer that from UML prespective

it mean each book has only one author but each author can write many books

sorry if i miss understand anything as i do not know about django
hope it help and have a nice day

3

OK, thanks for your answer,
So can you please also explain what author: Author[1..*] (second field in the Book box) means?

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you welcome it say the same thing 1 here mean one author … linked to * many books

plus sign mean this filed is private
you can check this about uml it’s not complete one but it would help
https://www.tutorialspoint.com/uml/uml_basic_notations.htm

hope it help and have a nice day

1 Like
5

the Author[1…*] is probably a mistake because the diagram in the Express module is different (in this article: Express Tutorial Part 3: Using a Database (with Mongoose) - Learn web development | MDN):

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if the example mentioned that each book has only one author then you are right

am i understand you right ?

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in both Django and Express modules LocalLibrary’s example, each book has exactly one author

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then update the page with the image you posted and @chrisdavidmills will be notified about that change
so if we miss something he can revert the change just login there and update it

and have a nice day both of you

9

Thanks @justsomeone @Rafael_Green

Yes, the multiplicity specified inside the Book class on Django image is inconsistent with the multiplicity shown next to the Author class and all the rest of the code. I will fix it.

As @justsomeone says, the difference between 1 and 1…* is “exactly 1” and “one or more”. Of course in real life a book may have multiple authors; in the examples I sometimes simplify things to make it easy to demonstrate both 1:1 and 1:many relationships.

@Rafael_Green Thanks for your recent fixes/proposals for the examples. I’m going to be looking at the Django example again properly in the coming month - so any feedback is not being ignored, just not got to it yet. Keep it coming.

1 Like
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thanks for your good work @hamishwillee

nice job @Rafael_Green

and have a nice day both of you :slight_smile:

1 Like
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:+1: The Django and Express tutorials are very well written and it’s very enjoyable to read them