Please help modelling "has-a-vector-of-3" relationship
26 views
Skip to first unread message
Ronald Fischer
May 21, 2014, 8:18:28 AM5/21/14
to rubyonra...@googlegroups.com
In my application, I have 3 models. Let's call them X, Y and Z for
brevity. Their relationship are as follows:
- One X has an arbitrary number (maybe zero) items of type Y.
- One Y has 2 or 3 items of type Z. Moreover, these items are *ordered*,
i.e. I need to record somehow, which is the first one, which the second
etc.
- From a certain Z, I need to find out which Y it belongs to, and from a
Y, I need to find out which X it belongs to.
- When an X is deleted, the contained Y need to be destroyed too.
- When an Y is deleted, the contained Z need to be destroyed too.
Here is what I have so far:
The mapping between X and Y is straightforward. When generating the
model for Y, I included a field X:references. Within X.db, I included a
has_many: :y, dependent: :destroy
For the mapping between Y and Z, I didn't come up with a convincing
solution. When generating the model Z, I included a field Y:references,
but how do I model the 2 or 3 Z entities within Z?
From a database viewpoint, I would need three fields (with different
names, say z1, z2 and z3), which all contain the ID of a certain row
within z. The field z3 might be NULL (in SQL terms), while z1 and z2
must always be provided.
But how do I define this in the "ruby generate model" command? The only
field type which could store a reference to another table, would be
'references', but don't see how this would help me in this case.
I already thought about this workaround: I do a has_many relationship
from Y to Z, and my application makes sure, that there are only 2 or 3 Z
elements assigned at one time. In addition, I add to my Z table a field,
which says whether it is number one, two or three within this group.
This should work, but can this really be called an elegant design?
--
Posted via http://www.ruby-forum.com/.
brevity. Their relationship are as follows:
- One X has an arbitrary number (maybe zero) items of type Y.
- One Y has 2 or 3 items of type Z. Moreover, these items are *ordered*,
i.e. I need to record somehow, which is the first one, which the second
etc.
- From a certain Z, I need to find out which Y it belongs to, and from a
Y, I need to find out which X it belongs to.
- When an X is deleted, the contained Y need to be destroyed too.
- When an Y is deleted, the contained Z need to be destroyed too.
Here is what I have so far:
The mapping between X and Y is straightforward. When generating the
model for Y, I included a field X:references. Within X.db, I included a
has_many: :y, dependent: :destroy
For the mapping between Y and Z, I didn't come up with a convincing
solution. When generating the model Z, I included a field Y:references,
but how do I model the 2 or 3 Z entities within Z?
From a database viewpoint, I would need three fields (with different
names, say z1, z2 and z3), which all contain the ID of a certain row
within z. The field z3 might be NULL (in SQL terms), while z1 and z2
must always be provided.
But how do I define this in the "ruby generate model" command? The only
field type which could store a reference to another table, would be
'references', but don't see how this would help me in this case.
I already thought about this workaround: I do a has_many relationship
from Y to Z, and my application makes sure, that there are only 2 or 3 Z
elements assigned at one time. In addition, I add to my Z table a field,
which says whether it is number one, two or three within this group.
This should work, but can this really be called an elegant design?
--
Posted via http://www.ruby-forum.com/.
tamouse pontiki
May 21, 2014, 11:14:58 AM5/21/14
to rubyonra...@googlegroups.com
inheritance...
Ronald Fischer
May 21, 2014, 11:47:37 AM5/21/14
to rubyonra...@googlegroups.com
tamouse m. wrote in post #1146720:
Thank you for the confirmation.
> As much as I hate to say is, this *might* be a case for single table
> inheritance...
So be it! ;-)
> inheritance...
Thank you for the confirmation.
Reply all
Reply to author
Forward
0 new messages