Hello,
You can get this new version of the patch at the following URL:
http://www.xsoli.com/sqlobject-inheritance-2a.patch
Here is a new patch that add simple inheritance to SQLObject 0.8.1.
For those who tried one of my patch, here are the modification from
the first and second patch:
* As suggested by Ian Bicking, each child classes now have the same
ID than the parent class. No more need for childID column and
parent foreignKey (with a small speed boost).
* No more need to call getSubClass as the 'latest' child will always
be returned when an instance of a class is created.
* This patch now seems to works correctly with addColumn, delColumn,
addJoin and delJoin.
* This patch now correctly retreive old objects from the database
(thanks to Oleg Broytmann for finding this bug)
With this patch, the following code:
class Person(SQLObject):
_inheritable = 1 # I want this class to be inherited
firstName = StringCol()
lastName = StringCol()
class Employee(Person):
_inheritable = 0 # If I don't want this class to be inherited
position = StringCol()
will generate the following tables:
CREATE TABLE person (
id INT PRIMARY KEY,
child_name TEXT,
first_name TEXT,
last_name TEXT
);
CREATE TABLE employee (
id INT PRIMARY KEY,
position TEXT
)
A new class attribute '_inheritable' is added. When this new
attribute is set to 1, the class is marked 'inheritable' and a new
colomns will automatically be added: childName (TEXT).
Each class that inherits from a parent class will get the same ID as
the parent class. So, there is no need to keep track of parent ID and
child ID as they are the same.
The column childName will contain the name of the child class (for
exemple 'Employee'). This will permit to a class to always return its
child class if available (a person that is also an employee will always
return an instance of the employee class).
For exemple, the following code:
p = Person(firstName='John', lastName='Doe')
e = Employee(firstName='Jane', lastName='Doe', position='Chief')
p2 = Person(1)
Will create the following data in the database:
*Person*
id
child_name
first_name
last_name
0
Null
John
Doe
1
Employee
Jane
Doe
*Employee*
id
position
1
Chief
You will still be able to ask for the attribute normally:
e.firstName will return Jane and setting it will write the new value in
the person table.
If you use p2, as p2 is a person object, you will get an employee
object.
person(0) will return a Person instance and will have the following
attributes: firstName and lastName
person(1) or employee(1) will each return the same Employee instance and
will have the following attributes: firstName, lastName and position
Also, deleting a person or an employee that are linked will destroy
both entries as one would expect.
The SQLObject q magic also work. Using this select are valid:
Employee.select(Employee.q.firstName == 'Jane' & Employee.q.position ==
'Chief') will return Jane Doe
Employee.select(Person.q.firstName == 'Jane' & Employee.q.position ==
'Chief') will return Jane Doe
Employee.select(Employee.q.lastName == 'Doe') will only return Jane Doe
(as Joe isn't an employee)
Person.select(Person.q.lastName == 'Doe') will return both entries
The SQL where clause will contain additional clauses when used with
'inherited' classes. These clauses are the link between the id and the
parent id. This will look like the following request:
SELECT employee.id, employee.id, employee.first_name,
employee.last_name, from employee FROM person, employee WHERE
person.first_name = 'Jane' AND employee.position = 'Chief' AND person.id
= employee.id
Some limitation or notice about this patch:
* Only simple inheritance will work. It is not possible to inherits
from multiple SQLObject classes.
* It is possible to inherits from an inherited class and this will
works well. In the above exemple, you can have a Chief class that
inherits from Employee and all parents attributes will be
available through the Chief class.
* You may not redefine a parent column in a inherited class (this
will raise an exception).
* If you don't want 'childName' columns in your last class (one that
will never be inherited), you must set '_inheritable' to 0 in this
class.
* I made this patch because I needed to be able to have automatic
inheritance with linked table.
* This patch works for me, it may not works for you. I tried to do
my best but it is possible that I broke some things... So, there
is no warranty that this patch will work.
* This patch is released under the LGPL (GNU Lesser General Public
License) as the original SQLObject code.
* Thanks to Ian Bicking for SQLObject, this is a wonderful python
module.
* If you have suggestion, bugs, or patch to this patch, you can
contact me at <sqlobject xsoli.com>
Thanks,
Daniel Savard
XSOLI Inc.
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