Hi:
I'm working in a pylons application and I have a DB which has the
following structure (I haven't depicted the many-to-many tables
between, for instance, a computer and a rule for the sake of
simplicity):
----------------- ----------------------
-------------------------------------
| computers | | computer_sets | |
computer_sets_computers |
----------------- ---------------------
--------------------------------------
id id <----------\
id
name name \
name
description description \
description
rule_id ---| rule_id --\ \
ip | \ \
ip
| \
\------------ computer_set_id
| \
| -------- \
| | rules | \
| -------- \
|----------> id <-----------\
name
description
enabled
There are some points to highlight:
1) A computer_set is only a container of computer_set_computer
entities. However, a computer_set_computer is almost identical to a
computer entity, with only one difference: a computer entity can be in
a rule alone while a computer_set_computer cannot be in a rule; it is
considered to be in a rule only as part of a computer_set
2) I have created classes for each of these entities: Computer,
ComputerSet, ComputerSet_Computer, Rule
However, I have to do the following: I need to be able to query my DB
for both Computer and ComputerSet_Computer objects. I mean, I need to
display the list of those computers no matter whether or not they
belong to a ComputerSet (though when iterating through those objects,
I need to know the type of the object). Furthermore, I need to get a
Query object to be able to apply slices (to control pagination :) and
gain performance.
I have tried using UNION and UNION_ALL between the computer and
computer_set_computer tables, but I get errors because the tables
don't contain the same number of columns.
Thanks for your time,
Sandor
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