Unable of Many-to-one cardinalities


#1

Hi everybody,
I am designing an ERD for a database. When I try to connect already existing tables, I don’t get relation Many-To-One as an option. Can somebody tell me why is that and how can I get it to be possible? Thank you :slight_smile:


#2

Hi Nedim,

We only allow setting the cardinality of a relationship as many to one for conceptual/logical ERD. You can change the kind of ERD from physical to conceptual/logical by opening the diagram’s specification dialog box, and select the desired kind in the “Data model” field.

Hope this helps,

Antony.


#3

Hi @antony,

Thanks for your reply. When I change it to Conceptual and add new tables form Model Explorer, I still can’t do it with those tables. Can you help me about this?


#4

If you create new table from Model Explorer, then you will have to change the data model manually via its specification dialog box, since “Physical” is the default data model. Therefore it is recommended that you create an ERD and change it to conceptual, then add new tables and relationships to this diagram. That way the newly created tables and relationships will pick up the data model of the ERD automatically.


#6

Hi @antony,

Again, thanks for the reply. I set my whole Diagram to Conceptual, then add new tables, which are also conceptual and I still don’t get the Many-To-One option. The only “new” thing I get is the ‘Generalization’. Do you know what am I missing? Thank you in advance :slight_smile:

Best regards,
Nedim


#7

Hi Nedim,

Sorry that I haven’t explained clearly, the palette currently does not support creating the many-to-one relationship even for concept ERD, but you can create any one kind of relationship (say, one-to-one), and then change its from/to end cardinality via its specification dialog box as screenshot.

erd

Hope this could answer your question,

Antony.


#8

Thank you very much, this helped me a lot. I am just interested why is it like this, that you cannot make a Many-To-One relationship, but you can make another to be like that?

Thank you,
Nedim


#9

Sorry about the inconvenience caused, it is because we only place the most commonly used kinds of relationships in the palette. Beside changing the from/to end cardinality via the specification dialog box, you can also right-click on either end of the relationship in the diagram to change it from the popup menu, which should be easier.

erd